DTC 12

- Chart - Code 12 No Distributor Reference Pulses:

- Wiring Diagram for Code 12 No Distributor Reference Pulses:

CODE 12, NO DISTRIBUTOR REFERENCE PULSES

CIRCUIT DESCRIPTION
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 engine not running,and is used for the 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. If the problem clears, Code 41 will store.

CHART DESCRIPTION
1. This step checks for a poor connection at the EST 4 wire 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. This step determines if a reference pulse is being sent to the ECM. Voltage should normally 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 the ECM, the terminal must be removed from the connector.
3. With an open circuit, there is still a small amount of voltage at the ECM. It will not increase when the throttle is opened. If the circuit from Terminal "10" to the module is not opened or grounded, the source of no signal is the module itself.