If you have a trouble code on your ’81 (this is the old “OBD I” system), you have to have the ECM spit out the trouble codes so you can see what the problem is. It’s not possible to guess what the problem could be based on the fact that you have a check engine light. If there is an engine malfunction detected by any one of the numerous sensors connected to the ECM, a trouble code will be stored in the memory, and your check engine light will be triggered by any multitude of issues. To pull the code from the ECM, you will need to locate your ALDL (Assembly Line Diagnostic Link) connector. It is normally located right under the dash around the steering wheel area to the right. For some reason, I seem to remember that my '82 ALDL was in or near the ashtray in the center console. The ALDL has a top row and a bottom row of connector terminals: The terminal to the far right on the top row is the “A” terminal, and the one to the left of it is the “B”. "A” is ground, and “B” is diagnostics.

To pull the codes, turn the ignition switch to the “ON” position (do not start the car). Using a paper clip, jump between terminals A and B. You will see the SES (Service Engine Soon) light flash out a code. It will flash out each code three times. The first code you will get will be a code 12. It will be a single flash, followed by a short pause, then two flashes. It will then pause for about two seconds or so, and flash the code again until it reads out three times. The code(s) after this will be your trouble code(s). Write them down. When you get back to code 12 it is finished.

Once you are done writing down all your trouble codes, turn off the ignition and remove the jumper between terminals A & B. To reset the codes, simply pull the ECM fuse (Blue 15A) for one minute. Doing this will reset the ECM back to factory settings, and the driving parameters will have to be relearned (the car will do this itself).

Here are the most common codes. No - the codes are not for emissions - they are for detecting, troubleshooting, and correcting significant engine operating problems. For a complete list, along with the solutions to the problem codes, just look in your Service Manual – there’s an entire section in the manual devoted to this.

12
ERROR CODE DIAGNOSTIC SYSTEM FUNCTIONING CORRECTLY

13
OXYGEN SENSOR CIRCUIT OPEN

14
COOLANT TEMPERATURE SENSOR (CTS) CIRCUIT (HIGH TEMP)

15
COOLANT TEMPERATURE SENSOR (CTS) CIRCUIT (LOW TEMP)

21
THROTTLE POSITION SENSOR (TPS) CIRCUIT (HIGH)

22
THROTTLE POSITION SENSOR (TPS) CIRCUIT (LOW)

23
MANIFOLD AIR TEMP (MAT) or INTAKE AIR TEMP (IAT) CIRCUIT (LOW TEMP)

24
VEHICLE SPEED SENSOR (VSS) CIRCUIT

25
MANIFOLD AIR TEMP (MAT) or INTAKE AIR TEMP (IAT) CIRCUIT (HIGH TEMP)

26
QUAD-DRIVER (QDM) ERROR (if applicable)

32
EXHAUST GAS RECIRCULATION (EGR) CIRCUIT

33
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR (VOLTAGE HIGH-LOW VACUUM)

34
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR (VOLTAGE LOW-HIGH VACUUM)

35
IDLE SPEED CONTROL (ISC) CIRCUIT

41
CYLINDER SELECT ERROR (FAULTY OR INCORRECT MEM-CAL)

42
ELECTRONIC SPARK TIMING (EST) CIRCUIT

43
ELECTRONIC SPARK CONTROL (ESC) CIRCUIT

44
OXYGEN SENSOR CIRCUIT (LEAN EXHAUST)

45
OXYGEN SENSOR CIRCUIT (RICH EXHAUST)

51
MEM-CAL ERROR (FAULTY OR INCORRECT MEM-CAL)

53
SYSTEM OVER VOLTAGE

54
FUEL PUMP CIRCUIT (LOW VOLTAGE)

55
ECM ERROR

61
DEGRADED OXYGEN SENSOR

66
A/C PRESSURE SENSOR CIRCUIT

 

You're welcome.

Lars

 

Slight correction to Lars post. The connector for the 81 is under the ashtray in the center console. It is a single row of pins (just for the 81, lars is correct that the 82 had two rows). Jumper the right two pins (I think, not near my car, but it is the two pins with the cutout between them). A small screwdriver fits right in jumps the pins. See picture below

I cannot agree more with Lars, that trying to debug this without first reading the codes is usually a colossal waist of time and money. I have seen so many people debug by "I knew a guy who change the TPS and that fixed it" When the fault codes clearly indicate the O2 sensor is bad.

Read the codes, there may be many, start with the first. The 1981 service manual has very good diagnostic charts for each code. If you don't have the service manual I can get you scans of the charts.

The 81 was the first year ECM so it has a smaller set of fault codes than Lars list, but it will be in there. Let us know what the code is and I can help you with what's in the Service manual. These issues seem overwhelming at first, but they usually turn out with a simple sensor replacement or wire repair.

 

 

Must be Time to demolish these Forums..just everyone buy the dang Service/ Shop manuals..and quit posting questions.
geeeeeez !

 

That light never comes on in my 77.

 

I have two service books now thanks for the great informatin helped me big time. Bad ECM will have to replace.

 

Posting all the diagnostic charts for all the codes would not be possible. The OP never reported which trouble code(s) he had, making any Forum diagnostic impossible. Instead, he was correctly advised on how to read the trouble codes, and given good info on where to find the diagnostic charts for the applicable codes. If he had posted the trouble code(s), suggestions could have been made - I posted the trouble code list above, but I can't post the troubleshooting guide for all those codes. That would be crazy... You cannot troubleshoot or work on an ECM-controlled car without the Service Manual and the diagnostic charts - the OP was given good advice.

Lars