GM Prizm/Nova 1985-1993 Repair Guide

Fault Codes

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See Figures 1, 2, 3 and 4

READING



To read the code(s) from the ECM:

  1. The following initial conditions must be met or the code will not be transmitted from the ECM:
    1. Battery voltage above 11 volts
    2.  
    3. Throttle plate fully closed - keep your foot off the accelerator
    4.  
    5. Transmission selector in neutral
    6.  
    7. All accessory switches off
    8.  

  2.  
  3. Turn the ignition switch ON, but DO NOT start the engine.
  4.  
  5. Use a service (jumper) wire to short both terminals of the engine check connector, located under the hood near the wiper motor.
  6.  



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Fig. Fig. 1: Location of the check engine connector - 1988 VIN code 5 engine

  1. The diagnosis code(s) will be indicated by the number of flashes of the Check Engine light. If the system is normal, the light will blink repeatedly every 1 / 2 second. This indication is displayed when no codes are stored in the ECM. It serves as a confirmation the the ECM has nothing to tell you - all is well. If a fault code is stored, its 2 digit code will be indicated in the pattern of the flashing. For example, code 21 would be indicated by 2 flashes, a pause, and 1 flash. There will be a 1 1 / 2 second pause between the first and second digit of a code. If more than 1 code is stored, the next will be transmitted after a 2 1 / 2 second pause. Once all the codes have been flashed, the system will wait 4 1 / 2 seconds and repeat the entire series. It will continue sending the fault codes as long as the initial conditions are met and the engine check connector is shorted across terminal T and E1 .
  2.  

If more than 1 code is stored, they will be delivered in numerical order from the lowest to the highest, regardless of which code occurred first. The order of the codes DOES NOT indicate the order of occurrence.



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Fig. Fig. 2: Examples of a multiple code display - 1988 VIN code 5

  1. After the code(s) have been read and recorded, turn the ignition switch to OFF and disconnect the jumper wire.
  2.  


WARNING
Disconnecting the wire with the ignition ON may cause severe damage to the ECM.



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Fig. Fig. 3: Trouble codes for ECM - 1988 VIN code 5 engine



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Fig. Fig. 4: Trouble codes for ECM - 1988 VIN code 5 engine

Resetting The Check Engine Light

See Figures 5 through 22

Once the codes have been read and recorded, the memory on the ECM may be cleared of any stored codes by removing the power to the ECM for at least 20 seconds. This is most easily done by removing the STOP fuse from the fusebox for the necessary period of time.


WARNING
The ignition MUST be OFF when the fuse is removed and reinstalled. Serious and disabling damage may occur if this precaution is not followed.

Remember that the codes are there to indicate a problem area. Don't clear the code just to get the dashboard light off - find the problem and fix it for keeps. If you erase the code and ignore the problem, the code will reset (when the engine is restarted) if the problem is still present.

The necessary time to clear the computer increases as the temperature drops. To be safe, remove the fuse for a full minute under all conditions. The system can also be cleared by disconnecting the negative battery cable, but this will require resetting other memory devices such as the clock and/or radio. If for any reason the memory does not clear, any stored codes will be retained. Any time the ECM is cleared, the car should be driven and then re-checked to confirm a normal signal from the ECM.

In the event of any mechanical work requiring the disconnection of the negative battery cable, the ECM should be interrogated for stored codes before removing the cable. Once the cable is removed, the codes will be lost almost immediately. Always check for stored codes before beginning any other diagnostic work.



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Fig. Fig. 5: Component location - 1985-88 VIN code 4 engine (49 state and Canada)



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Fig. Fig. 6: Component location - 1985-88 VIN code 4 engine (California)



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Fig. Fig. 7: Vacuum and wiring diagram - 1985-88 VIN code 4 engine (49 state and Canada)



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Fig. Fig. 8: Vacuum and wiring diagram - 1985-88 VIN code 4 engine (California)



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Fig. Fig. 9: Component location - 1987 VIN code 4 engine (California)



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Fig. Fig. 10: Component location - 1987 VIN code 4 engine (49 state and Canada)



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Fig. Fig. 11: Vacuum and wiring diagram - 1987 VIN code 4 engine (California)



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Fig. Fig. 12: Vacuum and wiring diagram - 1987 VIN code 4 engine (49 state and Canada)



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Fig. Fig. 13: Component location - 1988 VIN code 4 engine (California with man. trans.)



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Fig. Fig. 14: Component location - 1988 VIN code 4 engine (49 state and Canada with man. trans.)



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Fig. Fig. 15: Component location - 1988 VIN code 4 engine (California with auto. trans.)



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Fig. Fig. 16: Component location - 1988 VIN code 4 engine (49 state and Canada with auto. trans.)



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Fig. Fig. 17: Vacuum and wiring diagrams - 1988 VIN code 4 engine (49 state and Canada with man. trans.)



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Fig. Fig. 18: Vacuum and wiring diagrams - 1988 VIN code 4 engine (California with man. trans.)



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Fig. Fig. 19: Vacuum and wiring diagrams - 1988 VIN code 4 engine (California with auto. trans.)



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Fig. Fig. 20: Vacuum and wiring diagrams - 1988 VIN code 4 engine (49 state and Canada with auto. trans.)



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Fig. Fig. 21: Component location - 1988 VIN code 5 engine



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Fig. Fig. 22: Vacuum routing - 1988 VIN code 5 engine

 
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