1994 Geo Prizm Base, AutomaticFACTORY OEM SERVICE PROCEDURE

Trouble Code Definitions

NOTE: Trouble codes will be recorded at various operating times. Some codes require sensor or switch operation for 5 seconds and others may require longer under certain conditions. Some codes may not set in a service bay operational mode.
TROUBLE CODE IDENTIFICATION

Code Circuit Affected Probable Cause
12 No RPM Signal No Signal
13 No RPM Signal No Signal
14 Ignition Signal No Signal
16 (1) PCM Control Signal PCM Failure
21 Oxygen Sensor Open/Short Circuit
22 Coolant Temp. Sensor Open/Short Circuit
24 Intake Air Temp. Sensor Open/Short Circuit
25 Oxygen Sensor Lean Exhaust Indicated
26 Oxygen Sensor Rich Exhaust Indicated
27 (2) Sub-Oxygen Sensor Open/Short Circuit
31 MAP Sensor Open/Short Circuit
41 Throttle Position Sensor Open/Short Circuit
42 Vehicle Speed Sensor Open/Short Circuit
43 Crank Signal No Signal
51 Switch Condition Signal No Signal
52 (1) Knock Sensor Open/Short Circuit
71 (2) EGR System Out Of Calibration
(1) Prizm LSi (VIN 8) only.
(2) California models only.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.