1993 Geo Prizm Base, StandardFACTORY OEM SERVICE PROCEDURE

Trouble Code Definitions

FAULT 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 (2) 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 (1) Sub-O2 Sensor Open/Short Circuit
31 MAP Sensor Open/Short Circuit
41 Throttle Position Sensor Open/Short Circuit
42 Vehicle Speed Sensor Incorrect Signal Voltage
43 Crank Signal No Signal
51 Switch Condition Signal No Signal Present
52 (2) Knock Sensor Signal Open/Short Circuit
71 (1) EGR Temp. Sensor Out Of Calibration
(1) California models only.
(2) Prizm LSi (VIN 8) only.
Factory Service Tools

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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.

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