ECM Trouble Codes

Click here for how to read the codes.

  • Code 12 - No Reference Pulses to ECM
  • Code 13 - Oxygen sensor circuit
  • Code 14 - Coolant sensor circuit
  • Code 15 - Coolant sensor circuit
  • Code 21 - Throttle Position Sensor
  • Code 22 - Throttle Position Sensor
  • Code 23 - Manifold Air Temperature (V6 only)
  • Code 24 - Vehicle Speed Sensor
  • Code 25 - Manifold Air Temperature (V6 only)
  • Code 32 - Exhaust Gas Recirculation system (V6 only)
  • Code 33 - Manifold Air Pressure sensor
  • Code 34 - Manifold Air Pressure sensor
  • Code 35 - Idle Air Control
  • Code 42 - Electronic Spark Timing
  • Code 44 - Lean exhaust
  • Code 45 - Rich exhaust
  • Code 51 - PROM
  • Code 52 - Fuel CALPAK (V6 only)
  • Code 53 - System over-voltage (V6 only)
  • Code 55 - ECM
    •  Note that component replacement may NOT solve the problem in all cases.

    Code 12 - No Reference Pulses to ECM

    This code will flash whenever the diagnostic terminal is grounded with the ignition in run, and the engine off. If this code appears while the engine is running, no reference pulses from the distributor are reaching the ECM.

    Code 13 - Oxygen sensor circuit

    Check for a misadjusted throttle position sensor. Check the wiring and connectors from the oxygen sensor. Replace the oxygen sensor.

    Code 14 - Coolant sensor circuit

    If engine is experiencing overheating, the problem must be fixed before continuing. Check all wiring and connectors associated with the coolant temperature sensor. Replace the coolant temperature sensor.

    Code 15 - Coolant sensor circuit

    If engine is experiencing overheating, the problem must be fixed before continuing. Check all wiring and connectors associated with the coolant temperature sensor. Check the wiring connections at the ECM.

    Code 21 - Throttle Position Sensor

    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

    Check the TPS adjustment. Check the ECM connector. Replace the TPS.

    Code 23 - Manifold Air Temperature (V6 only)

    Check the MAT sensor, wiring and connectors for an open sensor circuit. Replace the MAT sensor.

    Code 24 - Vehicle Speed Sensor

    A fault in this circuit should only be detected when the vehicle is moving. Disregard this code if it is set when the drive wheels are not turning. Check the connections at the ECM. Check the TPS setting.

    Code 25 - Manifold Air Temperature (V6 only)

    Check the voltage signal from the MAT sensor to the ECM. It should be above 4 volts.

    Code 32 - Exhaust Gas Recirculation system (V6 only)

    The EGR solenoid should not be energized and vacuum should not pass to the EGR valve. The diagnostic switch should close at about 2 inches of vacuum. With vacuum applied, the switch should close. Check the EGR vacuum lines for leaks. Replace the EGR solenoid. Replace the EGR valve.

    Code 33 - Manifold Air Pressure sensor

    Check the vacuum hoses from the MAP sensor. Check the electrical connections at the ECM. Replace the MAP sensor.

    Code 34 - Manifold Air Pressure sensor

    This code will be 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 - Idle Air Control

    This code will be set when the closed throttle speed is 50 RPM above or below the correct idle speed for 30 seconds. Check for vacuum leaks. Replace the IAC.

    Code 42 - Electronic Spark Timing

    If the vehicle will not start and run, check the wire leading to terminal 12 of the ECM. Check the EST wire (terminal 19 of the ECM) leading to the HEI module (terminal E). Check all distributor wires. Check the wire leading from EST terminal A to ECM terminal 12, and the wire from EST terminal A to ECM terminal 3. Replace the HEI module. Note this service bulletin regarding code 42.

    Code 44 - Lean Exhaust

    Check the ECM wiring connections, particularly terminals 15 and 8. Check for vacuum leakage at the TBI base gasket, vacuum hoses or the intake manifold gasket. Replace the oxygen sensor.

    Code 45 - Rich Exhaust

    Check the evaporative charcoal canister and its components for the presence of fuel. Replace the oxygen sensor.

    Code 51 - PROM

    Make sure that the PROM is properly installed in the ECM. Replace the PROM.

    Code 52 - Fuel CALPAK (V6 only)

    Check the CALPAK PROM to insure proper installation. Replace the PROM.

    Code 53 - System over voltage (V6 only)

    This code will be set if the voltage at ECM terminal B2 is greater than 17.1 volts for 2 seconds. Check the charging system.

    Code 55 - ECM

    Be sure that the ECM ground connections are tight. If they are, replace the ECM.

    How to read the codes

    When the Service Engine Soon (Check Engine) light comes on, the ECM has detected a problem with one of the sensor circuits in the car, and it sets a trouble code. The ECM holds stored trouble codes in memory as long as it has power from the battery. To retrieve the stored trouble codes, do the following:

    1. Remove the black trim plate on the center console where the cigerette lighter is.
    2. Take a paperclip or wire, and ground the two terminals on the top, closest to the passenger side of the car.
    3. Watch the Service Engine Soon (Check Engine) light.

    It will flash a series of codes at you. First, it should flash:

    FLASH-PAUSE-FLASH-FLASH. That is 1-2, code 12. This signifies that the ECM is not recieving reference pulses from the distributor, and therefore that the car is not running.

    It will flash this code three times, with a long pause between each code. If there are any stored trouble codes, it will flash them after this, starting with the lowest numbered codes, up to the highest numbered, each one repeated three times. It does NOT flash the codes back in the order in which they were set.

    One more example. If you see the following:

    FLASH-pause-FLASH-FLASH-long pause
    FLASH-pause-FLASH-FLASH-long pause
    FLASH-pause-FLASH-FLASH-long pause
    FLASH-pause-FLASH-FLASH-FLASH-long pause
    FLASH-pause-FLASH-FLASH-FLASH-long pause
    FLASH-pause-FLASH-FLASH-FLASH-long pause
    FLASH-FLASH-FLASH-FLASH-pause-FLASH-FLASH-FLASH-FLASH-long pause
    FLASH-FLASH-FLASH-FLASH-pause-FLASH-FLASH-FLASH-FLASH-long pause
    FLASH-FLASH-FLASH-FLASH-pause-FLASH-FLASH-FLASH-FLASH-long pause
    FLASH-pause-FLASH-FLASH-long pause
    FLASH-pause-FLASH-FLASH-long pause
    FLASH-pause-FLASH-FLASH-long pause

    Then your ECM is giving you code 13 (oxygen sensor) and code 44 (lean exhaust). (In case you are wondering, these are the codes I got when my Oxygen sensor on my 2m4 went bad.)

    From: Sketch

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