I have an 89 with maft pro setup and speed density. While tuning the code 21 popped up, I did some ckecking and found the heater circuit of the O2 sensor was open. I replaced the O2 sensor, cleared the code, and restarted..... code came back. I inspected the engine harness and found that the heater circuit wires may have been contacting one another. Fixed that, cleared code, restarted, and code returned. I then tried another ECU thinking maybe something was fried but the code came back. I'm lost.... what do I need to check next?
HELP!!! code 21
- Thread starter teebone
- Start date
You need to verify heater resistance at the ECU or check current anywhere along the circuit. That said there are other causes for code 21 depending on model year and where the car was meant to be sold but properly checking the heater circuit first would be the best place to start.