GM OBD Trouble Code 12
No Distributor Reference Pulse (Diagnostic Test Active)
The Engine Control Module uses the distributor reference pulse to calculate the engine speed. On newer engines, the Crank Shaft Position Sensor performs this function.
Fault Code Description
12 - No Distributor reference pulse (diagnostic test active)
Symptoms
- When flashing the Check Engine Light to read codes, code 12 will always display first, indicating the diagnostic system is active
- The engine will not run with a "hard" code 12 set
Common Problems
- Chances are you will never need to diagnose a code 12. Rather, the problem would be a crank, no-start condition.
- If code 12 does not flash, that would indicate a communication problem with the ECM.
- Code 12 does not show when reading codes with a scan tool. If there is a communication problem, the scan tool will let you know.
Related Questions
See what others have asked about this, or visit the Questions page to ask your own question.
The car has 54 thousand miles, second owner and never has had good gas milage
The light was not on when we bought it a week ago
High Quality Repairs
Your auto repair done right, only the work you need with no add ons.
Never Overpay
Our free estimator calculates a custom price for your vehicle repair.
Guaranteed Repairs
Rest easy knowing you're covered by a local warranty.
Are You a Shop Owner?
Learn how to grow your business with RepairPal