Whether you own a classic Chevrolet, Cadillac, or any other GM model, understanding the OBD1 codes specific to your vehicle is crucial for effective troubleshooting and maintenance.
With our complete list of OBD1 codes, you can gain the knowledge and insights needed to decipher GM OBD1 codes, empowering you to take control of your GM car’s health and performance.
Towards the end of the article, you can perform a self-diagnostic test with or without a scanner, and learn how to read the trouble codes, interpret them, and identify the faulty component or sensor.
Keep reading to find out more!
GM OBD1 Codes List and Definition [FULL]
Free Download: Full GM OBD1 Trouble Codes List and Meaning PDF
Note: Use the search box in the table below to quickly find the specific code you’re looking for.
| Code | Definition |
|---|---|
| Code 12 | No distributor reference pulse (diagnostic test active) |
| Code 13 | Oxygen sensor circuit open or no activity |
| Code 14 | Engine coolant temp sensor error (high temp indicated) |
| Code 15 | Engine coolant temp sensor error (low temp indicated) |
| Code 16 | System voltage too low |
| Code 17 | Camshaft position sensor error |
| Code 21 | Throttle Position sensor error (signal high) |
| Code 22 | Throttle position sensor error (signal low) |
| Code 23 | Intake air temp sensor error (low temp indicated) |
| Code 24 | Vehicle speed sensor error (open circuit or no activity) |
| Code 25 | Intake air temp sensor error (high temp indicated) |
| Code 26 | Quad Driver Module (QDM A) error |
| Code 28 | Auto transmission range pressure switch error |
| Code 31 | Waste gate solenoid circuit error |
| Code 31 | Gear Position Switch (PRNDL) error |
| Code 32 | Baro sensor circuit error/ EGR circuit error/ MAP sensor signal open |
| Code 33 | MAP sensor circuit error (signal high indicating low vacuum) |
| Code 34 | MAP sensor circuit error (signal low indicating high vacuum) |
| Code 35 | IAC problem or idle error |
| Code 36 | MAF sensor error/ 24x crankshaft position sensor circuit error/ 4T60-E shifting error |
| Code 37 | TCC brake switch circuit error |
| Code 38 | TCC brake switch circuit error |
| Code 39 | Clutch switch circuit error/ Torque converter clutch error |
| Code 41 | Ignition control error/ MEM-CAL error/ Computer Controlled Ignition Cam Sensor Signal error |
| Code 42 | Ignition bypass circuit error |
| Code 43 | Knock sensor error |
| Code 44 | Oxygen sensor error (lean condition indicated) |
| Code 45 | Oxygen sensor error (rich condition indicated) |
| Code 46 | Pass-Key II (VATS) system error – circuit out of freq range |
| Code 47 | UART (serial data) circuit error |
| Code 51 | PROM error/ Incorrect MEM-CAL |
| Code 52 | Fuel cal-pak incorrect or missing |
| Code 53 | System voltage too high |
| Code 53 | Digital EGR Valve solenoid 1 error |
| Code 54 | Fuel pump circuit low voltage/ Digital EGR Valve solenoid 2 error |
| Code 55 | ECM error/Digital EGR Valve solenoid 3 error |
| Code 56 | Quad Driver Module (QDM B) error |
| Code 57 | Boost Control error |
| Code 58 | Trans fluid temp sensor circuit error (low voltage)/ VATS system error |
| Code 59 | Trans fluid temp sensor circuit error (high voltage) |
| Code 61 | A/C system performance |
| Code 63 | Right bank O2 sensor circuit error/ MAP sensor circuit signal voltage high (low vacuum indicated) |
| Code 64 | Right bank O2 sensor lean exhaust indicated/ MAP sensor circuit signal voltage low (high vacuum indicated) |
| Code 65 | Right bank O2 sensor rich exhaust indicated |
| Code 66 | A/C pressure sensor circuit error (low pressure indicated) |
| Code 67 | A/C pressure sensor circuit error |
| Code 68 | A/C clutch relay circuit error (shorted to ground) |
| Code 69 | A/C clutch relay circuit error (open circuit indicated)/ A/C high pressure switch error |
| Code 70 | A/C pressure sensor circuit error (high pressure indicated) |
| Code 71 | A/C evaporator temp sensor circuit error (low temp indicated) |
| Code 72 | VSS signal circuit error |
| Code 73 | A/C evaporator temp sensor circuit error (high temp indicated) |
| Code 75 | Digital EGR solenoid #1 circuit error |
| Code 76 | Digital EGR solenoid #2 circuit error |
| Code 77 | Digital EGR solenoid #3 circuit error |
| Code 79 | Transmission fluid over temp |
| Code 80 | Transmission component slipping |
| Code 82 | 3x Crankshaft position sensor circuit error |
| Code 85 | PROM error |
| Code 86 | ECM Analog/Digital error |
| Code 87 | EEPROM error (flash memory error) |
| Code 90 | TCC error |
| Code 93 | Transmission pressure control solenoid circuit error |
| Code 96 | Transmission system voltage low |
| Code 98 | Invalid PCM program |
| Code 99 | Invalid PCM program |
How to Read OBD1 Codes for GM with a Paper Clip
Do you ever get frustrated with why the check engine light keeps flashing on your vehicle and wanna know what it means? But you don’t have a dedicated scanner to diagnose the issue.
Don’t worry. I will show you an easy way to read your OBD1 codes using a tiny paper clip. Here are the steps to follow to diagnose the faulty system in your Chevy vehicle:
- First, locate the diagnostic plug underneath the dashboard. It should include 12 female pins and has a black plastic casing.
- Unroll a paper clip and fold it into a U or V shape.
- Insert the ends of the unrolled paper clip through pins A and B, which are the two top right pins on the plug. These steps automatically shift the vehicle to diagnostic mode.
- Next, start the ignition but be careful not to start the engine.
- Fix your eyes on the instrument cluster. Your primary focus should be the check engine light which should start blinking at any moment.
- The diagnostic systems communicate via iterative blinking of the check engine light. Counting the number of blinks should tell you the error code.
- The vehicle groups error codes in 2 digits, and each is iterated 3 times.
- The first time the vehicle will blink once, pause, then twice to symbolize code 12. This code means the start of the diagnosis. The code is repeated thrice before trouble codes begin displaying.
- The vehicle will iterate through the error codes, which you should record with a pen and paper, then finish with code 12, indicating the end of the process.
- Turn the ignition off and pull out the paper clip before looking up the meaning of the codes in Google.
How to Read OBD1 Codes on GM with a Scanner
Why improvise when you could get a scanner to perform the same function as the paper clip. GM scanners help in reading the error codes without jeopardizing the system’s electronic circuitry. Here is how to use it:
- Insert the scanner into the diagnostic plug, which should be located beneath the dashboard. Ensure that it is inserted correctly for its pins to mesh with the plug’s pins A and B.
- Turn on the ignition but be careful not to rev up the engine.
- Check the check engine light. It should flash once then twice, indicating a code 12 that represents the start of diagnostic mode. Each code will be iterated thrice.
- Next, the check engine light will flash several times to indicate the trouble codes. You should note and record them with a piece of paper and pen. It would help if you got a partner to assist by writing down the codes or counting the number of flashes you might miss if you did the work independently.
- After the system displays all the error codes, it will flash a code 12 indicating the end of the diagnosis.
- Switch off the ignition.
- Look up the error code in Google for clarity on the faulty component. Or you could come back to this page after this procedure and look it down below in our GM OBD1 code list.
How to Clear GM OBD1 Codes
GM OBD1 codes are super easy to remove. You don’t have to do anything at times, and starting your car three or four times will eliminate the trouble codes. Nevertheless, there is a quicker method that is also relatively easy to execute. Here is how to do it:
- Locate the battery in your car, which should be located somewhere underneath the engine compartment.
- Loosen the bolt reinforcing the plug to the negative terminal using a wrench. The negative terminal should have a minus symbol on it, and a black cable should be mounted using a plug on it.
- Disconnect the cable from the negative terminal.
- Wait for 30 to 60 seconds before reconnecting the cable to the negative terminal.
- Tighten the bolt with the wrench.
- Turn on the ignition and check if the error code is removed.
- If the check engine light is still flashing, repeat the above procedure a second time, only that this time you wait for 1 to 2 minutes.
Final Thoughts
In conclusion, our OBD1 codes list post is designed to be your ultimate guide in tackling diagnostic challenges for your classic GM vehicle.
We’d love to hear from you, so please feel free to leave a comment if you have any questions or wanna share your success stories about fixing your car’s problems. Your insights and experiences are incredibly valuable for any GM owner to address their issues.
And if you’re looking for the proper scanner for your vintage GM, take advantage of our enticing OBD1 scanner review.
Thanks for taking the time to read this post!
References
- GM OBD I Trouble Code Chart, ace.carcareconnect.com
- List of all of the GM OBD1 codes, thirdgen.org
