OBD Code 12 - No Distributor Reference Pulse (Diagnostic Test Active)
The Engine Control Module-ECM uses the distributor reference pulse to calculate the engine speed. On
newer engines, the Crank Shaft Position Sensor performs this function.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
OBD Code 46 - Pass-Key II System Error - Circuit out of Frequency Range
- 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.
The ECM receives a signal from the Pass-Key module. When the correct signal is
received, the ECM will allow the engine to start and run. Please review
the RepairPal article on the GM Pass-Key Anti-theft
systems for more information.Symptoms:
OBD Code 43 - Knock Sensor error
- Faulty ignition lock cylinder
The ECM receives a signal from the Knock Sensor based on the amount of engine ping detected. The ECM
uses information from this sensor to help calculate fuel delivery and spark timing.Symptoms:
- Engine ping
- Lack of power
OBD Code 55 - End Test.
- Faulty Knock sensor
- Poor connection at Knock sensor
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