Repairs to vehicles

When it comes to automotive repair, there are several methods of approaching the problem. Let’s look at: known problems first, maintenance as pair, comprehensive versus fix just what is broken, as well as a few diagnostic approaches.

Known Problems First

Until we correct all the known problems in a system, we can not know if they are effecting the portion of the system we are concerned about. Often times tracking down the cause of one problem will reveal the cause of others. Use this method with a bit of common sense, replacing a gas cap for an evaporative leak will most likely not fix a misfire. However, often times vacuum leaks cause many, many problems. (For a specific example of fix know problems first, visit here )
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Here is a list of the most common check engine lights (CELs P Codes) and their common causes and common symptoms.

To diagnose many of the problems, you will need little more than a test light, a volt meter, a vacuum gauge and maybe a can of brake clean. A hand held code puller/ data reader such as this….

This is a relatively inexpensive scan tool made by autolink. It pulls codes as well as reads and displays your basic drive-ability data. I would recommend this to anyone who wants to repair any modern car (1996 or newer). I have one, and I use it all day long. It is very handy.

automotive repair scan tool

Oxygen sensor codes

Oxygen sensor codes generally mean the oxygen sensor has failed. The oxygen sensor is in the exhaust, and reads the exhaust in order for the computer to finely tune the amount of fuel the engine needs.

Oxygen Sensor

Bank 1 sensor is on the side of the motor with the number one cylinder, bank 2 is the other side. Sensor 1 is in the exhaust, on the motor side (upstream) of the catalytic converter, sensor 2 is on the other side (down stream) of the cat. Check and make sure the sensor has power, ground and it’s reference voltage (usually 5 or 1 volts). The signal should switch back and forth between low and high voltage.

Make sure the vehicle is not stuck in a lean or rich condition. Introduce a vacuum leak, and see if the signal voltage changes. Then add fuel (brake clean through a vacuum port) and see if the signal changes. 6 times out of 10 the sensor is bad, 3 times out of 10 there is a vacuum leak or rich condition. The codes that are for heater circuit are almost always the sensor, otherwise there is a broken wire somewhere.

Symptoms include, poor gas mileage, poor power, rough idle, fail emission testing. Vehicle should start and run even if the oxygen sensor is unplugged.

  • P0051 HO2S Heater Control Circuit Low (Bank 2 Sensor 1)
  • P0052 HO2S Heater Control Circuit High (Bank 2 Sensor 1)
  • P0130 02 Sensor Circuit Malfunction (Bank 1 Sensor 1)
  • P0131 02 Sensor Circuit Low Voltage (Bank 1 Sensor 1)
  • P0132 02 Sensor Circuit High Voltage (Bank 1 Sensor 1)
  • P0133 02 Sensor Circuit Slow Response (Bank 1 Sensor 1)
  • P0134 02 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)
  • P0135 02 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)
  • P0136 02 Sensor Circuit Malfunction (Bank 1 Sensor 2)
  • P0137 02 Sensor Circuit Low Voltage (Bank 1 Sensor 2)
  • P0138 02 Sensor Circuit High Voltage (Bank 1 Sensor 2)
  • P0139 02 Sensor Circuit Slow Response (Bank 1 Sensor 2)
  • P0140 02 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)
  • P0141 02 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)
  • P0150 02 Sensor Circuit Malfunction (Bank 2 Sensor 1)
  • P0151 02 Sensor Circuit Low Voltage (Bank 2 Sensor 1)
  • P0152 02 Sensor Circuit High Voltage (Bank 2 Sensor 1)
  • P0153 02 Sensor Circuit Slow Response (Bank 2 Sensor 1)
  • P0154 02 Sensor Circuit No Activity Detected (Bank 2 Sensor 1)
  • P0155 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
  • P0156 02 Sensor Circuit Malfunction (Bank 2 Sensor 2)
  • P0157 02 Sensor Circuit Low Voltage (Bank 2 Sensor 2)
  • P0158 02 Sensor Circuit High Voltage (Bank 2 Sensor 2)
  • P0159 02 Sensor Circuit Slow Response (Bank 2 Sensor 2)
  • P0160 02 Sensor Circuit No Activity Detected (Bank 2 Sensor 2)
  • P0161 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2)

Mass Air Flow (MAF) Codes

Mass Air Flow (MAF) Codes generally mean the MAF has gone bad or there is a major vacuum leak. The MAF is the main way the engine monitors the amount of air going into the engine in order to determine how much fuel the engine needs.

Mass Air Flow Sensor

First and foremost check to see if there are any vacuum leaks. Watch your short term and long term fuel trims. If there is a vacuum leak, they should be adding fuel. Spray the intake and intake manifold with brake clean and look for the fuel trims to go back to 0, and even start pulling fuel. If the fuel trims, particularly the short term trims, pull fuel, you have found a vacuum leak.

Check and make sure the sensor has power, ground and it’s reference voltage (usually 5 or 1 volts). If the car runs with a MAF code, tap the MAF while the engine is running and see if the engine bobbles or dies. Often times a bad MAF will cause the engine to not start.

Other symptoms would be extremely poor gas mileage, extremely poor running condition, and fail emission testing. 5 times out of 10 the sensor is bad, 4 times out of 10 there is a vacuum leak.

  • P0100 Mass or Volume Air Flow Circuit Malfunction
  • P0101 Mass or Volume Air Flow Circuit Range/Performance Problem
  • P0102 Mass or Volume Air Flow Circuit Low Input
  • P0103 Mass or Volume Air Flow Circuit High Input
  • P0104 Mass or Volume Air Flow Circuit Intermittent

Manifold Absolute Pressure (MAP)

Manifold Absolute Pressure (MAP) codes generally mean the MAP is bad, or there is a major vacuum leak. The MAP sensor is one major way the computer decides how much fuel the engine needs. Some cars have a stand alone MAP, some have a MAP sensor built into the MAF.

First and foremost check to see if there are any vacuum leaks. Cars that use only a MAP to meter fuel will often be rich if there is a vacuum leak. Watch your short term and long term fuel trims. Spray the intake and intake manifold with brake clean and look for the fuel trims to start pulling fuel. If the fuel trims, particularly the short term trims, pull fuel, you have found a vacuum leak.

Check and make sure the sensor has power, ground and it’s reference voltage (usually 5 or 1 volts). Also make sure there is good vacuum going into the MAP sensor.

Often times a bad MAP will cause the engine to not start. Other symptoms would be extremely poor gas mileage, extremely poor running condition, and fail emission testing. 5 times out of 10 the sensor is bad, 4 times out of 10 there is a vacuum leak.

  • P0105 Manifold Absolute Pressure/Barometric Pressure Circuit Malfunction
  • P0106 Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance Problem
  • P0107 Manifold Absolute Pressure/Barometric Pressure Circuit Low Input

Engine Coolant Temperature (ECT)

Engine Coolant Temperature (ECT) codes generally mean the coolant temperature sensor is bad, or the car is out of coolant. The ECT effects the amount of fuel the computer supplies the engine. Engines need more fuel to start and run when they are cold. Keep in mind the engine almost always has two ECT sensors, one for the gauge and one for the computer.

Wait for the car to cool down, and make sure it is full of coolant. If the car is full of coolant, put a new sensor in, they are cheep and easy.

Symptoms of a bad ECT sensor include, poor gas mileage, hard to start, no start, car over heating due to cooling fans not coming on, and fail emission testing. Very common failure on all makes, remember there are almost always two, two wire ECT sensors, one for the gauge one for the computer.

6 out of 10 times the sensor is bad, 4 out of 10 times the vehicle is low on coolant.

  • P0115 Engine Coolant Temperature Circuit Malfunction
  • P0116 Engine Coolant Temperature Circuit Range/Performance Problem
  • P0117 Engine Coolant Temperature Circuit Low Input
  • P0118 Engine Coolant Temperature Circuit High Input

Throttle Position Sensor (TPS)

Throttle Position Sensor (TPS) codes generally mean the TPS is bad, or the throttle plate is some how out of adjustment. The throttle body may be dirty, the throttle cable may be to tight, the throttle adjustment screw may need to be tweaked. If the vehicle is drive by wire ( a vehicle which does not have a throttle cable) the throttle body may just need to be reset through a factory type scan tool.

Symptoms include poor or no throttle response, poor gas mileage, low or high idle, improper shifting ( with automatic transmissions).

8 out of 10 times the sensor is bad.

  • P0121 Throttle Position Sensor/Switch A Circuit Range/Performance Problem
  • P0122 Throttle Position Sensor/Switch A Circuit Low Input
  • P0123 Throttle Position Sensor/Switch A Circuit High Input

Coolant temperature too low

The vehicle is not reaching operating temperatures. Almost always a thermostat stuck open, but can also be a faulty engine coolant temperature sensor.

Symptoms include poor gas mileage.

P0125 Insufficient Coolant Temperature for Closed Loop Fuel Control
P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

Gross fuel trim failure

Gross fuel trim failure are common and have multiple causes. Vacuum leak, bad oxygen sensor, fuel leaking from fuel pressure regulator into manifold, failed fuel injector, bad coolant temperature (ECT) sensor, bad manifold pressure (MAP) sensor, bad mass air flow (MAF) sensor.

First determine if the trims are lean or rich. Then go down the list of causes until you find a gross failure. ECT sensor reading 0 degrees even though the vehicle is hot. A MAP or MAF sensor at 0 volts. A Major vacuum leak, the kind you can hear and is the size of your finger. Generally gross fuel trim failures are easy to find.

P0170 Fuel Trim Malfunction (Bank 1)
P0171 System too Lean (Bank 1)
P0172 System too Rich (Bank 1)
P0173 Fuel Trim Malfunction (Bank 2)
P0174 System too Lean (Bank 2)
P0175 System too Rich (Bank 2)

Misfire

Misfire codes – suck, squish, bang, blow gone wrong. Poor quality or incorrect ignition parts, failed injector, burnt valve, improper camshaft/ crankshaft timing, improper ignition timing, low quality gas (water in fuel), low compression (bad rings).

If you have a particular cylinder misfire, then it is a little easier to find the cause. If you have several misfires, or a random/ multiple misfires, check all the cylinders and also pay close attention to fuel trims. Pull the spark plug, check to ensure it is the proper plug. Check the gap and look for a burn mark down the side. Do a compression check. If compression is low, proceed with a leak down test.

If compression is good, put the plug back in and run the vehicle with a ignition stress tester in line.

Ignition Tester

This is a tester you can put in line in your ignition system. By making the spark jump a gap, you can stress the ignition system and find a failing system. Very handy. If the spark is ok, check to ensure you injector is clicking.

If you suspect a faulty part, (coil, spark plug, injector) you can always move that one part to another cylinder, clear the codes and then see if the misfire moves to the new cylinder.

P0300 Random/Multiple Cylinder Misfire Detected
P0301 Cylinder 1 Misfire Detected
P0302 Cylinder 2 Misfire Detected
P0303 Cylinder 3 Misfire Detected
P0304 Cylinder 4 Misfire Detected
P0305 Cylinder 5 Misfire Detected
P0306 Cylinder 6 Misfire Detected
P0307 Cylinder 7 Misfire Detected
P0308 Cylinder 8 Misfire Detected
P0309 Cylinder 9 Misfire Detected
P0310 Cylinder 10 Misfire Detected
P0311 Cylinder 11 Misfire Detected
P0312 Cylinder 12 Misfire Detected

Knock sensor

Knock sensor codes generally mean the knock sensor has gone bad. Can be wiring, almost never is. Very common problem on imports.

P0325 Knock Sensor 1 Circuit Malfunction (Bank I or Single Sensor)
P0326 Knock Sensor 1 Circuit Range/Performance (Bank 1 or Single sensor)
P0327 Knock Sensor 1 Circuit Low Input (Bank I or Single Sensor)
P0328 Knock Sensor 1 Circuit High Input (Bank I or Single Sensor)
P0329 Knock Sensor 1 Circuit Intermittent (Bank 1 or Single Sensor)
P0330 Knock Sensor 2 Circuit Malfunction (Bank 2)
P0331 Knock Sensor 2 Circuit Range/Performance (Bank 2)
P0332 Knock Sensor 2 Circuit Low Input (Bank 2)
P0333 Knock Sensor 2 Circuit High Input (Bank 2)
P0334 Knock Sensor 2 Circuit Intermittent (Bank 2)

Crankshaft Position

Crankshaft Position generally means the sensor has gone bad, or a timing belt that has skipped a tooth. Many vehicles, particularly Audi and VW will throw a Crankshaft Position if the are turned over too many times with out starting. For example, if the fuel pump goes out, and you try long enough to start the car, a Crankshaft Position code will appear.

P0335 Crankshaft Position Sensor A Circuit Malfunction
P0336 Crankshaft Position Sensor A Circuit Range/Performance
P0337 Crankshaft Position Sensor A Circuit Low Input
P0338 Crankshaft Position Sensor A Circuit High Input
P0339 Crankshaft Position Sensor A Circuit Intermittent

Camshaft Position

Camshaft Position generally means the sensor has gone bad or a timing belt that has skipped a tooth. Could also be a clogged or failed variable valve timing solenoid gone bad. Generally, a vehicle uses the crankshaft position sensor for gross fuel and spark control, and the camshaft position sensor for fine tuning. Therefore, a bad camshaft sensor may cause a rough idle, or poor gas mileage, or poor performance, but may the vehicle will still run. On other cars loss of a camshaft position sensor will cause the vehicle to not start at all.

P0340 Camshaft Position Sensor Circuit Malfunction
P0341 Camshaft Position Sensor Circuit Range/Performance
P0342 Camshaft Position Sensor Circuit Low Input
P0343 Camshaft Position Sensor Circuit High Input
P0344 Camshaft Position Sensor Circuit Intermittent
P0345 Camshaft Position Sensor A Circuit Malfunction (Bank 2)
P0346 Camshaft Position Sensor A Circuit Range/Performance (Bank 2)
P0347 Camshaft Position Sensor A Circuit Low Input (Bank 2)
P0348 Camshaft Position Sensor A Circuit High Input (Bank 2)
P0349 Camshaft Position Sensor A Circuit Intermittent (Bank 2)

Exhaust Gas Recirculation (EGR)

Exhaust Gas Recirculation (EGR) codes will rarely cause any type of drive-ability issues. The EGR system is mainly present to reduce emissions (NOX). The EGR valve could be bad, lack of vacuum to the actuator, actuator could be bad, ports could be clogged.

Many vehicles are equipped with an EGR temp sensor that tells the computer the EGR valve has opened, that sensor could be bad. Many cars use the MAP sensor to tell if the EGR valve has opened, so if you have a vacuum leak or a faulty MAP sensor, you could get an EGR could in error.

Check your vacuum supplies, ensure the EGR valve opens, whether electric or vacuum opened, and dig into the theory of how this particular vehicle opens, and monitors the EGR valve.

P0400 Exhaust Gas Recirculation Flow Malfunction
P0401 Exhaust Gas Recirculation Flow Insufficient Detected
P0402 Exhaust Gas Recirculation Flow Excessive Detected
P0403 Exhaust Gas Recirculation Circuit Malfunction
P0404 Exhaust Gas Recirculation Circuit Range/Performance

Secondary Air

Secondary Air codes will rarely cause any type of drive-ability issues. The Secondary Air Injection system is mainly present to reduce emissions. Check to see that the air pump, whether belt driven or electric, is moving air, and that the air is getting to the exhaust. Very common problem on VW and Audi due to broken plastic tubes that direct the air. Could also be turned on in error due to a vacuum leak or a bad oxygen sensor.

P0410 Secondary Air Injection System Malfunction
P0411 Secondary Air Injection System Incorrect Flow Detected

Catalyst (Cat)

Catalyst (Cat) codes generally mean the cat has gone bad. Can be causes by a bad oxygen sensor, but that is generally not normally the case. Very hard to test a cat without shop equipment.

Bad cats will rarely have any symptoms, if they are plugged they will cause poor gas mileage, rough running, lack of power.

P0420 Catalyst System Efficiency Below Threshold (Bank 1)
P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)
P0430 Catalyst System Efficiency Below Threshold (Bank 2)
P0431 Warm Up Catalyst Efficiency Below Threshold (Bank 2)

Evaporative Emission Control System

Evaporative Emission Control System codes are generally hard to diagnose without shop equipment. Your best bet is to replace the gas cap and hope for the best. If the code comes back, you will need a smoke machine to properly find the leak. Any decent shop will have one.

P0440 Evaporative Emission Control System Malfunction
P0442 Evaporative Emission Control System Leak Detected (small leak)
P0455 Evaporative Emission Control System Leak Detected (gross leak)

Fuel Level

Fuel Level codes generally mean the fuel level sensor in the tank has gone bad.

P0460 Fuel Level Sensor Circuit Malfunction
P0461 Fuel Level Sensor Circuit Range/Performance
P0462 Fuel Level Sensor Circuit Low Input
P0463 Fuel Level Sensor Circuit High Input
P0464 Fuel Level Sensor Circuit Intermittent

Vehicle Speed

Vehicle Speed codes generally mean the sensor has gone bad.

P0500 Vehicle Speed Sensor Malfunction
P0501 Vehicle Speed Sensor Range/Performance
P0502 Vehicle Speed Sensor Low Input
P0503 Vehicle Speed Sensor Intermittent/Erratic/High

Idle Control System

Idle Control System codes – vacuum leak, failed idle air control (IAC) valve, dirty throttle body. Basically the vehicle has lost the ability to control the idle, either due to the idle control system failing, or some fort of gross fuel trim failure.

P0505 Idle Control System Malfunction
P0506 Idle Control System RPM Lower Than Expected
P0507 Idle Control System RPM Higher Than Expected

Transmission

Transmission codes are never a good sign. Short of a bad solenoid, or maybe a bad torque converter, you generally are due for a transmission rebuild if you have any transmission codes present. Check the fluid level, top off with the proper fluid if low.

P0730 Incorrect Gear Ratio
P0731 Gear I Incorrect ratio
P0732 Gear 2 Incorrect ratio
P0733 Gear 3 Incorrect ratio
P0734 Gear 4 Incorrect ratio
P0735 Gear 5 Incorrect ratio
P0736 Reverse incorrect gear ratio
P0740 Torque Converter Clutch Circuit Malfunction
P0741 Torque Converter Clutch Circuit Performance or Stuck Off
P0742 Torque Converter Clutch Circuit Stock On
P0743 Torque Converter Clutch Circuit Electrical
P0744 Torque Converter Clutch Circuit Intermittent
P0510 Closed Throttle Position Switch Malfunction

A quick note about oil changes. All good techs will clean the mating surface on the oil filter housing. Furthermore they will also lube the oil filter gasket with oil. Almost no techs I have met will pre-fill the oil filter. By filling the filter with oil, you are reducing the time it takes for the engine to achieve oil pressure. A minor detail, but a detail I wish more techs took the time to perform. If you are using BG’s MOA, it’s an easy solution to add the MOA to the filter.

Wet Oil Filter

So the next time you go in for an oil change, ask them for a “wet filter”. They should know what you want, and if they don’t, maybe you need a new mechanic.

So you have a battery that keeps going dead. You have checked all the connections and the cables. They are clean and in good condition. You have replaced the battery or tested it, and it is o.k. and it’s full of water.

You’ve gone on to check or replace the alternator. It charges over 13.5 D/C volts even with a load on it. The A/C ripple is less than a volt (Put a test lead from a volt meter on the positive terminal and the main power output on the back of the alternator, switch the volt meter to A/C. ) If the alternator and the battery are both o.k., and the cables are in good condition, you most likely have a draw. A draw occurs anytime something that should turn of, doesn’t.
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Cold Engine Enrichment

A common complaint, especially when temperature start to drop is, “My car runs poorly cold, or my car is hard to start cold”. Both of these complaints are generally caused by a problem with cold start enrichment. In order for an engine to start and run cold, it requires more fuel than when it is hot. This condition where the engine needs more fuel cold is called cold start enrichment. Enrichment meaning a higher ratio of fuel to air.

If the car does not get the proper enrichment when cold, it will have trouble starting, or run poorly until the engine warms up. These complaints are mysterious at first, but once you learn the common causes, you can often cure them with little to no trouble.

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Whenever I recommend a new timing belt and water pump, I am often asked, “Can i do that myself?”. My short answer is, “No”. I would not recommend your average vehicle owner to attempt replacing their timing belt and water pump. We often see cars come in here with minor to major problems stemming from another shop installing a timing belt wrong.

That being said, here are some tips to help ensure the proper installation of a timing belt and water pump.
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Every repair order should include the four C’s. The four C’s of automotive repair are, complaint (or concern), cause, correction, confirm. As a technician, utilizing the four c system will ensure you repair a vehicle properly. Similarly, as a customer, looking to see that the four C’s are on your invoice will help ensure you are using a mechanic who knows the proper steps to repairing a vehicle.

We will use the example of a car overheating to demonstrate how to use the four c method. The repair order would say something in the realm of: “Customer states vehicle runs hot, please advise”. As a technician, your first step is to replicate the complaint. Whenever possible, quantify the complaint. Test drive the vehicle and watch the coolant temperature sensor. You can record the data, and add to the repair order, “Test drove vehicle, engine coolant temperature reaches 230 degrees Fahrenheit”.
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A frequent cause of heartache for technicians, and car owners alike, is the failed E-test. Truth be told, just about any properly running vehicle will pass emission testing. This post will not be a laundry list of cheats. Rather, this post will be a comprehensive list of repair information, to aid in actually repairing the vehicle so it is in accordance with emission standards.

Pre-Test Tips

First and foremost, make sure your catalytic converter (cat) is hot before you go to emission testing. A cat is just a honeycomb of metal that becomes so hot it burns any left over fuel the motor was unable to burn. In order to incinerate the left-overs, the cat must become extremely hot.

The best way to ensure your cat is hot, is to cruise your car down the highway for 15 to 20 minutes before you go to test the vehicle. The exhaust temperature is the hottest during light throttle cruise. Running the car down the highway will heat soak the cat, to ensure it will “lite off” during testing.

A good old fashioned top end de-carb is always a good idea before emission testing a vehicle. If you can get a full injector purge, that is best. Simply adding BG’s 44k to the gas tank and sucking a bottle of de-carb through a vacuum line also works well. The carbon in a motor becomes hotter than the normal parts of the motor, which can lead to detonation, misfire, or high NOX due to elevated combustion chamber temperatures.

Check your cooling system. A faulty cooling system can cause pre-detonation, and high nox. Let your car cool down, and make sure the coolant is full. Low coolant levels can casue multiple problems. As recommended here replace your radiator cap every spring.

Catalytic Converter

Emission Failures – Rules of thumb:

Understanding emission fialures requires undersanding the 5 gases that result from internal combustion. The 5 gases we measuer are HC, CO, CO2, O2 and NOX.

5 Gas Analyzer Specifications at 2000 RPM extended hold, in neutral or park.

  • HC = 100 PPM or less
  • CO = Less than 0.3 %
  • CO2 = Over 13.5 %
  • O2 = Less than 1 %
  • NOX = 100 – 700
  • Lambda, will vary, depending on if you are under load.

Nox is a result of high combustion chamber temperatures.

Common causes of high nox are:

  • a lean condition
    • a vacuum leak
    • a failed O2 sensor
    • a failed MAF (mass air flow) sensor
    • a failed MAP (manifold absolute pressure) sensor
  • Incorrect timing; either ignition or camshaft / crankshaft sync
    • too much ignition timing (too advanced)
    • improper crankshaft/ camshaft timing
  • a faulty cooling system
    • a failed coolant temperature sensor
    • low coolant level
    • inoperable cooling fans
  • a failed EGR (exhaust gas recirculation) system
    • Failed EGR Valve
    • Failed EGR Valve Solenoid
    • Clogged EGR Ports
  • a failed secondary air system.
  • a failed catalytic converter
  • a high compression motor

HC is from unburned or partially burnt fuel.

HC is generally a sign of misfire, but can also be that the engine is just way too rich. Common causes of HC are:

  • a rich or lean misfire
    • a failed O2 sensor
    • a failed MAF sensor
    • a failed coolant temperature sensor
    • a vacuum leak
    • dirty or sticking injectors
  • an ignition misfire
    • old or faulty ignition parts (plugs, wires, coils)
    • improper crankshaft/ camshaft timing
    • Improper ignition timing
  • a failed catalytic converter
  • a failed secondary air system

** A fuel leak (even a fuel vapor leak) near the tail pipe can also cause HC failure. The machines that suck the exhaust in and test it will also suck in the raw fuel and cause a HC failure.

High CO occurs when a car is too rich.

Common causes include

  • a failed O2 sensor
  • a failed MAF sensor
  • a failed MAP (manifold absolute pressure) sensor
  • leaking or sticking injectors
  • a failed coolant temperature sensor
  • a fuel pressure regulator leaking fuel into the vacuum port
  • too little ignition timing
  • a failed catalytic converter
  • a failed secondary air system

O2 is an indicator of air fuel metering

An O2 level over 1% indicates a lean condition.

CO2 is an indicator of over all engine health.

If CO2 is not over 13.5 % you have a general engine performance problem. Low compresion, poor ignition, faulty air fuel metering or the like.

You’ve probably noticed a pattern here. Honestly, there are a handful of systems which keep the car running properly, and the emissions low. As long as all the systems are working properly, you should be fine, the trick is determining which systems have failed.

You have to look at all five gasses to get an idea of what is going on. For example, if NOX and HC are both high, CO are low, and the idle is too high, I’d check for a vacuum leak causing lean misfire. To really hone in on the problem, you will also need a proper scan tool to watch data streams, and a 5 gas analyzer.

Correcting Emission Failures

automotive repair scan tool

This is a relatively inexpensive scan tool made by autolink. It pulls codes as well as reads and displays your basic drive-ability data. I would recommend this to anyone who wants to repair any modern car (1996 or newer). I have one, and i use it all day long.

Check your easy stuff first. Plug in a scan tool and run through your basic data, engine coolant temperature, MAF grams per second, baro pressure, intake air temperature, etc. and make sure nothing is out to lunch. For example, is the coolant temperature stuck at 0 degrees Celsius, causing the vehicle to permanently stay in cold start enrichment?

Check the Air and Fuel Metering

Make sure your vehicle is in fuel control. Modern cars have two fuel control modes, closed loop and open loop. When the car is in open loop, it is simply running a pre-made map, and makes little to no changes to the amount of fuel it delivers. When a vehicle is in closed loop, it is closely monitoring the engine and adjusting fuel and timing to create the proper air fuel ratio, and a good clean burn.

Learn more about closed loop Vs. Open loop by understnading how check engien lights work.

Watch your front oxygen sensor/s. The sensors should switch back and forth between high and low values. Many oxygen sensors are one volt systems, and will therefore switch between .02 and .98 volts. Other systems are five volt, some are 1.5 volt. The main thing to look for is rapid switching (every second or so) between low and high values. If the oxygen sensor is switching, then the ECU (engine control unit) is adjusting fuel. If an oxygen sensor is switching slowly, or sticking at a value, then there is a gross failure in the fuel control system (MAF, engine coolant temperature sensor, Oxygen sensor, etc.)

If the car is equipped with a MAF, check to make sure it is clean. A dirty MAF can cause a lean condition.

If you have an old style MAF, such as this:

mass airflow sensor

You can actually open these old MAF’s up and tune them. They are a simple flapper door that swings open as the engine draws more air in. The main downfall of these early MAF’s is that the spring wears out. As the spring wears out, the door will open further than it should, and the car will run rich. Watch your five gas analyzer and adjust it one click at a time. If you don’t have a five gas, you can always adjust a few clicks and then run it back through emission testing, it’s just far more time consuming. Generally speaking, you will need to tighten the spring two or three clicks per 100,000 miles.

Look for Ignition Problems

If you have a distributor on the car, set your timing. Ignition timing that is too far advanced will result in high NOX. Ignition timing that is too far retarded may result in high HC or CO.

While you are at it, also inspect your spark plugs to ensure they are new. Always, make sure you have the proper spark plug in your vehicle. Teh factory spark plug is always the best spark plug. If you are not sure what plugs to use, get a set form the dealership.

You can sometimes find a faulty ignition system by soaking the engine with water. The water will make it easier for the ignition system to arc to ground rather than going through the spark plug. If your car has coil on plug ignition, you can stress test the coils by making them jump a gap before the spark plug.

Ingnition Tester

This is a tester you can put in line in your ignition system. By making the spark jump a gap, you can stress the ignition system and find a failing system. Very handy.

As a last ditch effort, you can also check and ensure the crankshaft/ camshaft timing is correct. I have heard rumor of a new timing belt bringing a NOX failure back in line, once, but that would be fairly rare.

Check Emission Specific Components

You can also test your cat to verify it is working properly. First, you can install a back pressure tester in a pre-cat oxygen sensor bung. Rev the motor while in park or neutral and ensure the back pressure is low enough. If the back pressure is too high, you car is plugged, and requires replacement. You can also watch the front and rear O2 sensors to get an idea if the cat is working.

Further more, watch your five gas analyzer to verify the cat is working. Watch the five gas as the car warms up. Once the cold start enrichment has leveled off, drive the vehicle and watch the emissions. Before the cat is hot enough to light off, you will see all the emissions the car produces. At a certain point, if the cat is working, you will see the emissions drop as soon as the cat lites off.

Check your EGR system (if equipped), which recirculates exhaust gas to lower combustion chamber temperatures, and mainly lower NOX. Most EGR valves are opened by engine vacuum and a solenoid. With the engine running, apply vacuum to the EGR valve. If the valve works and the ports are clear, the engine should stumble and die. If the engine remains running, you have a faulty EGR system. If the Valve holds vacuum, but the engine doesn’t die, the ports are most likely clogged. If the EGR valve doesn’t hold vacuum, the valve is most likely bad. Certainly, the valve can be bad AND you have clogged ports.

Similarly, check the vacuum supply going into the EGR solenoid. if the solenoid has proper engine vacuum going into it, check the power and ground at the solenoid. Also, supply power and ground to the solenoid with the engine running. If the solenoid works, it will open and send vacuum over to the EGR valve.

Also check your secondary air system, if equipped. Secondary air system pumps air into pre-cat exhaust to help the cat light off. If your secondary air pump is electric, power it up and check to make sure it flows air. If your air pump is mechanical, let the engine idle and check to see if the air pump works. Mechanical air pumps often also utilize a solenoid which opens when the secondary air is required. Power up this solenoid and ensure it is working.

See also: Check engine light causes.

A sadly common problem we see around here is that the Ford gasoline motors will spit spark plugs out. Looks and sounds a bit like this.

Fortunately for us, and the owners of the effected motors, there is a easy and convenient repair. This kit allows us to cut new threads into the head with out removing it from the vehicle. An insert is then installed, and presto! the vehicle can once again accept an spark plug. Generally speaking, you will also need a new coil pack, as the retaining bracket will be broken. We also toss in the other seven spark plugs while we are at it. After the repair, it runs about as smooth as a Ford Triton motor could.

I’ve seen and tried lots of ways to get a tie rod end out of a knuckle; the torch, a pickle-fork, even a ball joint press. This approach is quick, clean, and leaves the threads of the tie rod end and the nut intact.

If you don’t have an air hammer, a regular hammer will work too. The key is to strike the hub and not the tie rod.

Pickle Fork