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    Reading and Diagnosing Engine Codes

    Reading and Diagnosing Engine Codes

    This article tells you how to read the Service Engine Soon Blink Codes on a A-Body cars. Obtaining blink codes was tested on a 1987 Pontiac 6000, but may be usable for other cars, though the tools needed and the connector and location may vary.

    First off, a bit of information on how the Service Engine Soon light works. This light is one of the indicators connected to the Engine Control Computer, or ECC. The ECC is what monitors the sensors under the hood on the engine in different areas, such as your Oxygen sensor, located on the manifold, your Coolant Temperature Sensor, oil, engine temperature and others. If your car has Fuel Injection, it also will control the mix of gas going into the engine. This computer essentially helps run your car's engine and reports back any possible problems with the engine or it's fluids, or other systems. The Service Engine Soon light will light up if there is a problem with the engine. It can light up for simple things like a ruptured vacuum hose, for example, or if a sensor is showing a fault in the system or may have failed itself. When the Service Engine Soon light comes on, you normally see it lit steady. But the ECC already has stored codes in it's memory to be read in diagnostics mode. This memory is semi-volitile. It can only be erased if the power to the battery is disconnected.

    The first thing you need to do is locate the ECC's interface panel. This is usually under the dash near the center of the car but more towards the driver's side on a 1987 Pontiac 6000. It's covered with a black plastic cover that snaps on/off. Once off, there reveals a set of two rows of connections to plug things in. Two on the top on the very right (last two) you'll see gold contacts are obvious. If you short these two (don't panic - it means "connect" them) with a special key (you can obtain one at most AutoZone locations which also do a blink code check for free if they are not busy). You might also get away with a paper clip or wire. Basically, you want to connect those two connections together. Don't worry about getting a shock. Handling a metal object and plugging into only these two with a simple metal clip or key is harmless and will not harm the computer.

    For the computer to give you the codes, you have to be in "accessory mode", which means to turn the key on, but not crank the engine. The engine must not be running.

    The way the ECC describes the codes is with a series of flashes which are repeated three times per code. The first and last code is always code 12. This means that the Service Engine Soon light will flash once, pause, then flash two more times. Then it will pause and do this again two more times (total of 3 times of one flash, a pause and then two flashes). The first set of flashes is the first digit (ie. one) and the second flash is the second digit (ie. two) meaning 12. Next it may flash some more. Just count the flashes and write that digit down. Then count the next set of flashes and write that digit down to the right of the first digit. This is your next number. This will repeat two more times.

    When the ECC is done indicating all the stored codes, it will again give you a code 12 three times to indicate it's finished reading the memory. It should then cycle all over again. You can then pull out the key or clip and turn off the ignition key.

    Let's give an example. Supposing the ECC stored codes 14 and 45 in it's memory when the service engine soon light was on. Go through the above procedure to read the codes. It should do the following:

    1 flash, pause, 2 flashes
    1 flash, pause, 2 flashes
    1 flash, pause, 2 flashes
    pause
    (then the above 4 lines will repeat two more times)
    1 flash, pause, 4 flashes
    1 flash, pause, 4 flashes
    1 flash, pause, 4 flashes
    pause
    (then the above 4 lines will repeat two more times)
    4 flashes, pause, 5 flashes
    4 flashes, pause, 5 flashes
    4 flashes, pause, 5 flashes
    pause
    (then the above 4 lines will repeat two more times)
    1 flash, pause, 2 flashes
    1 flash, pause, 2 flashes
    1 flash, pause, 2 flashes
    pause
    (then the above 4 lines will repeat two more times)
    This signifies the end of the diagnostics and will start from the beginning again.

    Once you have the codes written down, you'll want to pick up a copy of a Haynes book on Engine Blink Codes. This will help you match up the codes for your car. In the example above, code 14 referred to a fault with the Coolant Temperature Sensor and code 45 referred to an Oxygen Sensor fault. From there you can replace the appropriate part.

    After you have replaced the part, do not start the engine until you have unhooked the battery for about 15 seconds and then hook the battery back up. This clears the codes stored in the ECC memory so that you are less likely to get the same exact codes again if there is still a problem. This essentially gives you a clean slate to start with. If after clearing the ECC memory and starting the engine, you see the Service Engine Soon light go on again, turn off the engine and re-read the blink codes. If you find that it is till storing one or more of the same codes, then you still haven't fixed the problem(s). You'll want to try to fix or diagnose other problems that may be related.

    Sometimes, a sensor might not have actually failed, but may be sensing a problem in the area it's connected to. Check other lights on the dash. If you put the ignition in "accessory" mode (ie. on but not cranking the engine) all lights should light briefly to ensure they all are still operational. Be sure they are and then start the engine. Watch for any other lights that may relate to the blink codes. Is the engine running too hot, after you still get a code 14, for instance? Maybe it's your temperature sensor or your thermostat.

    The best way if you can't seem to fix the problem yourself is to take it to a qualified garage. They have a more sophisticated computer system that has a detailed diagnostics. The ECC only provides a very basic diagnostics which is meant for the auto owner to figure out what parts they can replace. If it's something more serious, a garage can find it easier. They usually charge a small to modest fee for this diagnostic procedure, however.

    Most things can be fixed by using the ECC diagnostics mode. This is your car's way of telling you what is wrong. However, I wouldn't recommend it be used to trace down loose or broken wires since the ECC mode is rather slow and you can't use it with the engine running. For loose/broken wires, a standard VOM (Volt/Ohm Meter) to test continuity would best be used.

    Another useful thing to have on hand in addition to the Haynes blink code manual is the Chilton's book and the actual shop manual for your vehicle. With these items, some decent tools, and the ability to read your ECC's blink codes, you are well on your way to being a "Shadetree" Mechanic.

    Below is a chart of some common engine control codes for A-Body vehicles:
    Code 12: Diagnostic Loop Start/Stop [ 1 flash, pause, 2 flashes ]
    This code will flash whenever the diagnostic terminal is grounded with the ignition turned On and the engine not running. If additional trouble codes are stored in the ECM they will appear after this code has flashed three times. If this code appears while the engine is running, no reference pulses from the distributor are reaching the ECM.
    Code 13: Oxygen Sensor [ 1 flash, pause, 3 flashes ]
    Check for a sticking or misadjusted throttle position sensor. Check the wiring and connectors from the oxygen sensor. Replace the oxygen sensor.
    Code 14: Coolant Sensor / High Temp[ 1 flash, pause, 4 flashes ]
    If the engine is experiencing overheating problems the problem must be rectified before continuing. Check all wiring and connectors associated with the coolant temperature sensor. Replace the coolant temperature sensor. If this doesn't clear the code, then it may be a bad line in the ECM unit itself. Check the ECM connectors and replace the ECM if necessary if that is the case.
    Code 15: Coolant Sensor / Low Temp [ 1 flash, pause, 5 flashes ]
    See above.
    Code 16: [ 1 flash, pause, 6 flashes ]
    Check the following:

    1. High battery voltage.
    2. Direct Ignition System (DIS) fault line is open or shorted to ground.
    Code 17: [ 1 flash, pause, 7 flashes ]
    RPM signal problem.
    Code 21: Throttle Position Sensor / Voltage High [ 2 flashes, pause, 1 flash ]
    Check for a sticking or misadjusted TPS plunger. Check all wiring and connections between the TPS and the ECM. Adjust or replace the TPS.
    Code 22: Throttle Position Sensor / Voltage Low [ 2 flashes, pause, 2 flashes ]
    Check the TPS adjustment. Check the ECM connector. Replace the TPS.
    Code 23: Mixture Control Solenoid [ 2 flashes, pause, 3 flashes ]
    The mixture control solenoid is open or grounded.
    Code 24: Vehicle Speed Sensor [ 2 flashes, pause, 4 flashes ]
    A fault in this circuit should be indicated only when the vehicle is in motion. Disregard Code 24 if it is set when the drive wheels are not turning. Check the connections at the ECM. Check the TPS setting.
    Code 25: [ 2 flashes, pause, 5 flashes ]
    Check the following:

    1. Vacuum Switching Valve Circuit is open or shorted to ground.
    2. ATS Sensor signal voltage is high.
    3. Manifold Air Temperature (MAT) Sensor signal voltage is low.
    Code 26: Quad Driver Module. [ 2 flashes, pause, 6 flashes ]
    Code 27: Transmission 2nd gear switch. [ 2 flashes, pause, 7 flashes ]
    Code 28: Transmission 3rd gear switch. [ 2 flashes, pause, 8 flashes ]
    Code 29: [ 2 flashes, pause, 9 flashes ]
    Check the following:

    1. Transmission 4th gear switch.
    2. Manifold Absolute Pressure (MAP) Sensor signal voltage is low.
    Code 31: [ 3 flashes, pause, 1 flash ]
    Check the following:

    1. Manifold Absolute Pressure (MAP) Sensor signal voltage is low.
    2. Fuel injector.
    3. CAM diagnostic.
    4. Governor Malfunction.
    5. Wastegate Eletrical Signal open or shorted to ground.
    Code 32 - Carberated: BARO Circuit Low [ 3 flashes, pause, 2 flashes ]
    Barometric pressure sensor circuit low.
    Code 32 - Fuel Injected: EGR [ 3 flashes, pause, 2 flashes ]
    Vacuum switch shorted to ground on start-up, switch not closed after the ECM has commanded the EGR for a specified period of time or the EGR solenoid circuit is open for specified period of time. Replace the EGR valve.
    Code 33: MAP Sensor [ 3 flashes, pause, 3 flashes ]
    Check the vacuum hoses from the MAP sensor. Check the electrical connections at the ECM. Replace the MAP sensor.
    Code 34: Vacuum Sensor or MAP Sensor [ 3 flashes, pause, 5 flashes ]
    Code 34 will set when the signal voltage from the MAP sensor is too low. Instead the ECM will substitute a fixed MAP value and use the TPS to control fuel delivery. Replace the MAP sensor.
    Code 35 - Carberated: ISC valve [ 3 flashes, pause, 5 flashes ]
    Idle Speed Control error. Replace the ISC.
    Code 36: [ 3 flashes, pause, 6 flashes ]
    Mass Air Flow (MAF) Sensor burn off circuit problem or a Direct Ignition System (DIS) fault resulting in an extra or missing pulses in Electronic Spark Timing (EST) signal.
    Code 38: Brake Switch Circuit Failure [ 3 flashes, pause, 8 flashes ]
    Code 39: Torque Converter Clutch (TCC) Circuit Fault [ 3 flashes, pause, 9 flashes ]
    Code 41: EST Circuit [ 4 flashes, pause, 1 flashes ]
    No distributor reference pulses to the ECM at specified engine vacuum.
    Code 42: Electronic Spark Timing [ 4 flashes, pause, 2 flashes ]
    Electronic Spark Timing bypass circuit or EST circuit is grounded or open. A malfunctioning HEI module can cause this code.
    Code 43: Electronic Spark Control Unit [ 4 flashes, pause, 3 flashes ]
    The ESC retard signal has been on for too long or the system has failed a functional check.
    Code 44: Lean Exhaust [ 4 flashes, pause, 4 flashes ]
    Check the ECM wiring connections, particularly terminals 15 and B. Check for vacuum leakage at the TBI base gasket, vacuum hoses or the intake manifold gasket. Replace the oxygen sensor.
    Code 45: Rich Exhaust [ 4 flashes, pause, 5 flashes ]
    Check the evaporative charcoal canister and its components for the presence of fuel. Replace the oxygen sensor.
    Code 46: [ 4 flashes, pause, 4 flashes ]
    Vehicle Anti-Theft Sytem (VATS) failure or Power Steering Switch failure.
    Code 47: ECM UART Problem [ 4 flashes, pause, 7 flashes ]
    Electronic Control Module (ECM) computer circuit problems with the Universal Asynchronous Receiver / Transmitter (UART) link.
    Code 48: Misfire [ 4 flashes, pause, 8 flashes ]
    Code 49: Vacuum Leak [ 4 flashes, pause, 9 flashes ]
    Code 51: PROM or MEM-CAL[ 5 flashes, pause, 1 flashes ]
    Make sure that the PROM or MEM-CAL is properly installed in the ECM. Replace the PROM or MEM-CAL.
    Code 52: CALPAK [ 5 flashes, pause, 2 flashes ]
    Check the CALPAK to insure proper installation. Replace the CALPAK.
    Code 53 - Carberated: EGR Valve [ 5 flashes, pause, 3 flashes ]
    Exhaust Gas Recirculation valve vacuum sensor has received improper EGR vacuum.
    Code 54 - Carberated: M/C Solenoid [ 5 flashes, pause, 4 flashes ]
    The mixture control solenoid voltage is high at the ECM because of a shorted M/C solenoid circuit and/or faulty ECM.
    Code 54 - Fuel Injected: [ 5 flashes, pause, 4 flashes ]
    Low fuel pump voltage. Sets when the fuel pump voltage is less than 2 volts when reference pules are being received.
    Code 55: ECM [ 5 flashes, pause, 5 flashes ]
    Be sure that the ECM ground connections are tight. If they are replace the ECM.
    Code 56: [ 5 flashes, pause, 6 flashes ]
    Corrosivity - Add Coolant. Or it could be Port Throttle System Vacuum Sensor problems.
    Code 58: Vehicle Anti-Theft System (VATS) Problem [ 5 flashes, pause, 8 flashes ]
    Code 62: [ 6 flashes, pause, 1 flashes ]
    Check the following:

    1. Oxygen (O2) Sensor Degraded.
    2. Port Throttle System Error.
    3. Cruise Control problems with the vent solenoid circuit.
    Code 62: [ 6 flashes, pause, 2 flashes ]
    Check the following:

    1. Gear switch input diagnostics.
    2. Oil Temperature Sensor signal voltage is high.
    3. Cruise Control problems with the vacuum solenoid circuit.
    Code 63: [ 6 flashes, pause, 3 flashes ]
    Check the following:

    1. Manifold Absolute Pressure (MAP) Sensor signal voltage is high.
    2. Small EGR failure.
    3. Right Oxygen (O2) Sensor failure.
    Code 64: [ 6 flashes, pause, 4 flashes ]
    Check the following:

    1. Manifold Absolute Pressure (MAP) Sensor signal voltage is low.
    2. Medium EGR failure.
    3. Right Oxygen (O2) Sensor lean condition indicated.
    Code 65: [ 6 flashes, pause, 5 flashes ]
    Check the following:

    1. Large EGR failure.
    2. Injector Peak / Hold Diagnostic.
    3. Right Oxygen (O2) Sensor rich condition indicated.
    4. Cruise Control Position Sensor Problem.
    Code 66: ECM [ 6 flashes, pause, 6 flashes ]
    Electronic Control Module (ECM) computer circuit problem: Internal reset occurred.
    Code 67: Cruise Control Switch Circuit Problems [ 6 flashes, pause, 7 flashes ]
    Code 68: Cruise Control System Circuit Problems [ 6 flashes, pause, 8 flashes ]
    Code 69: [ 6 flashes, pause, 9 flashes ]
    Check the following:

    1. Air Conditioner Pressure Switch circuit problems.
    2. Electronic Control Module (ECM) computer circuit.
    Code 88: Electronic Control Module (ECM) Computer Circuit [ 8 flashes, pause, 8 flashes ]
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