Code 12 - No Distributor Reference Pulses

Code 12 means the ECM is "ON" and sees no reference pulse from the distributor. This is a normal code with the ignition "ON" and the engine not running. Code 12 is not stored and will only flash when the fault is present. With engine running, Code 12 could mean an open or ground in distributor reference circuit. Code 41 will appear with Code 12 if engine is running with no distributor reference signal. If problem clears, Code 41 will store.

1. This test checks for a poor connection at EST 4-wire connector as being the source of no reference pulse. Check for corrosion, connector terminals not fully seated, or terminal not properly attached to wire. Terminal must be removed from the connector and carefully inspected.
2. This step determines if a reference pulse is being sent to the ECM. Voltage should increase as you go from idle to part throttle. A voltage increase indicates the signal is being generated by the module and fault is a bad connection at the ECM, or faulty ECM. To check the connection at ECM, terminal must be removed from connector.
3. With an open circuit, there is still a small amount of voltage at the ECM. It will not increase when throttle is opened. If circuit from term. "10" to module is not opened or grounded, source of no signal is the module.