GM OBDI Trouble Codes

OBDI trouble codes for 1988 – 1990 GM vehicles.

  • 13 – Oxygen sensor voltage stays between 0.35 and 0.55 volts for 60 seconds.
  • 14 – Coolant temperature sensor signal indicates a temperature of over 275° F for 2 seconds.
  • 15 – Coolant temperature sensor signal indicates a temperature colder than -27° F for 30 seconds after the engine has been running for at least 30 seconds.
  • 21 – TPS voltage was above 2.5 volts for 8 seconds when the MAP sensor signal showed manifold vacuum to be 15 pounds or more.
  • 22 – TPS voltage was under 0.2 volts for 2 seconds when the engine was running.
  • 23 – Inlet air temperature sensor signal showed an air temperature below -22° F after the engine has been running for 5 minutes.
  • 24 – Vehicle Speed Sensor (VSS) Circuit .
  • 25 – Inlet air temperature sensor signal showed an air temperature over 302° F after the engine has been running for 5 minutes.
  • 32 – EGR open command did not change MAP sensor signal. Normal EGR flow should cause slight decrease in manifold vacuum which would change MAP sensor signal.
  • 33 – MAP sensor signal voltage was too high (low vacuum) for 5 seconds when throttle opening was under 4%.
  • 34 – MAP sensor signal voltage was too low (high vacuum) when engine speed was under 1200 RPM or the engine speed was over 1200 RPM with a throttle position angle above 21%.
  • 35 – Idle Air Control (IAC) System .
  • 42 – The EST signal did not change when the ECM applied bypass voltage to the ignition module.
  • 43 – The ECM did not detect a knock signal during near wide open throttle operation with coolant temperature above 194° F or the knock signal was present for 5 seconds or more during normal engine operation. Electronic Spark Control (ESC) Circuit .
  • 44 – Oxygen sensor voltage was under 0.2 volts for 50 seconds of closed loop operation. (Lean Exhaust Indicated)
  • 45 – Oxygen sensor voltage was over 0.7 volts for 30 seconds of closed loop operation with a throttle angle between 2% and 20%.(Rich Exhaust Indicated)
  • 51 – PROM error. (MEM-CAL)
  • 52 – CALPAK error.Fuel CALPAK Missing .
  • 53 – System Over Voltage .
  • 54 – Fuel pump voltage was not present at fuel pump sense line for 2 seconds after the ECM has sent the fuel pump on command.(Low Voltage)
  • 55 – ECM error. Replace ECM.Faulty ECM

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