GM Full-Size Trucks 1980-1987 Repair Guide

DIAGNOSTIC TROUBLE CODES - GASOLINE ENGINES

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The following is a list of possible diagnostic trouble codes that could be stored in the Electronic Control Module's (ECM) memory. It should be noted that a diagnostic trouble code does not identify that a particular component has failed, but a problem in the circuit of that component has occurred. Therefore, if a code is found to be set in the ECM's memory, the related circuit must be checked completely. Be sure to perform the visual inspection before proceeding with additional testing and pay particular attention to wiring terminal connections at connectors for loose or corroded connections.



CODE 12 -No engine speed sensor reference pulses are being received by the ECM. This code is not stored in memory and will flash only while the fault is present. This code is normal when the ignition is on and the engine is not running.
 
Code 13 -The ECM has detected a problem in the oxygen sensor circuit. The engine must run at part throttle for at least four minutes before this code will set.
 
Code 14 -The ECM has detected a short in the coolant temperature sensor circuit. The engine must be running for at least two minutes before this code will set.
 
Code 15 -The ECM has detected a open in the coolant temperature sensor circuit. The engine must be running for at least two minutes before this code will set.
 
Code 21 -The ECM has detected that the throttle position sensor circuit voltage is high. This is and indication that the throttle position sensor is out of adjustment or an open in the circuit wiring has occurred. The engine must run for a least 30 seconds at idle before this code will set in the ECM's memory.
 
Code 22 -The ECM has detected that the throttle position sensor circuit voltage is low. This is an indication that the throttle position sensor circuit is shorted to ground. The engine must run for at least 2 minutes at 1250 rpm before this code will set in the ECM's memory.
 
Code 23 -The ECM has detected a short or open in the mixture control solenoid circuit on carbureted engines or the Manifold Air Temperature (MAT) signal is high indicating a open circuit on fuel injected vehicles.
 
Code 24 -No vehicle speed sensor signals are being received by the ECM. This is an indication that the circuit has an open or is shorted to ground. For this code to set, the vehicle must operate at any speed for 10 seconds.
 
Code 25 -The ECM has detected that the Manifold Air Temperature (MAT) signal is low indicating a short to ground on fuel injected vehicles.
 
Code 32 -The barometric pressure circuit signal voltage is low.
 
Code 33 -The ECM has detected low vacuum in the Manifold Absolute Pressure (MAP) sensor circuit.
 
Code 34 -The ECM has detected a problem in the vacuum sensor or the manifold absolute pressure sensor circuit. The engine must run for at least 2 minutes at curb idle before this code will set in the ECM's memory.
 
Code 35 -The ECM has detected a problem with the idle speed control circuit.
 
Code 41 - No distributor reference pulses to the ECM at specified engine vacuum.
 
Code 42 -Electronic spark timing bypass circuit is grounded or open.
 
Code 43 -Electronic spark control retard signal for too long a time period; causes a retard in the electronic spark timing.
 
Code 44 -The ECM has detected a lean exhaust condition. The engine must run for two minutes in closed loop operation before this code will set.
 
Code 45 -The ECM has detected a rich exhaust condition. The engine must run for two minutes in closed loop operation before this code will set.
 
Code 51 -Faulty or improperly installed PROM or calibration chip in the ECM. The ignition must be on for approximately 10 seconds before this code will set.
 



Code 53 - Exhaust Gas Recirculation (EGR) valve vacuum sensor circuit. The ECM has seen an improper EGR valve vacuum.
 
Code 54 -The ECM has detected a short in the mixture control solenoid and or a faulty ECM.
 
Code 55 -The ECM has detected a problem with itself. Replacement of the ECM is required.
 

 
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