DTC 12

Code 12:

Ignition Wiring Diagram:

CODE 12

NO ENGINE SPEED REFERENCE PULSE


Circuit Description:

Code 12 indicates the ECM is "ON" and sees no reference pulse from the distributor. This is a normal condition with the ignition "ON" and engine not running and is used for verification of ECM operation during the "Diagnostic Circuit Check." Code 12 is not stored and will only flash when the fault is present. With the engine running, Code 12 could mean an open or ground in the distributor reference circuit. Code 41 will appear with Code 12 if the engine is running with no distributor reference signal, and Code 41 will be stored even if the problem clears.


Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. This step checks for a poor connection at the EST connector as being the source of no distributor reference pulse. Check for corrosion, connector terminals not fully seated, or terminal not properly attached to the wire. The terminal must be removed from the connector and carefully inspected.


2. Voltage should normally be above .5 volt indicating that 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 the ECM, the terminal must be removed from the connector.

3. If CKT 430 from terminal "10" to the module is not opened or grounded, the source of no signal is the module itself.