How to retrieve trouble codes from an 1991 Chevy Caprice?

Answer 1

Locate the diagnostic connector: it's just under the dashboard, offset a little to the driver's side. Take a paper clip, straighten it out, then bend it into approximately a 1/2 " U shape. Alternately, if you want to do it like the pros, purchase a OBD-1 diagnostic reader. You could also just go to Auto Zone, as they will read it for you for free.

Place the "jumper" paper clip into the two diagnostic pin placements (A and B). Turn your key on, but do not start the car. Watch the check engine light: it will flash, if working correctly, a "12" code, which is the start of the ECU's trouble code memory. It will flash once, then twice, denoting a "12" code. This lets you know that the codes, if any, are about to run.

You'll need a list of codes for your car to know what it is telling you. The trouble codes will display twice. A 44, for example, will flash 4 times twice, then again 4 times twice. This gives you time to collect them, if there is more than one.

13 Open Oxygen Sensor Circuit

14 Coolant Temperature Sensor (High Temp Indicated)

15 Coolant Temperature Sensor (Low Temp Indicated)

21 Throttle Position Sensor (Signal Voltage High)

22 Throttle Position Sensor (Signal Voltage Low)

23 Manifold Air Temperature (MAT) Low Temp Indicated

24 Vehicle Speed Sensor (VSS) Circuit

25 Manifold Air Temperature (MAT) High Temp Indicated

32 Exhaust Gas Recirculation (EGR) Circuit

33 Manifold Absolute Pressure Sensor Circuit (High Sig.)

34 Manifold Absolute Pressure Sensor Circuit (Low Sig.)

42 Electronic Spark Timing (EST) Circuit

43 Electronic Spark Control (ESC) Circuit

44 Oxygen Sensor Circuit (Lean Exhaust Indicated)

45 Oxygen Sensor Circuit (Rich Exhaust Indicated)

51 Faulty PROM

54 Fuel Pump Circuit (Low Voltage)

55 ECM Error