DTC 12

Fig. 11 High energy ignition wiring circuit:

This trouble code is set during cranking and always results in a no start condition.
This trouble code indicates that the engine firing pulses generated by the pickup coil are not being received by the ECM. Possible causes of this condition are as follows:
a. No signal generated by High Energy Ignition.
b. Defective or improperly connected wiring.
c. ECM cannot process signal.
To diagnose a Code 12, proceed as follows:
1. Check HEI signal by disconnecting 4-way electrical connector at distributor. Connect voltmeter between distributor side connector pin B and ground.
2. Crank engine and observe voltage reading. Voltage at pin B should be between .5 and 2.0 volts. If reading of less than .5, or more than 2.0 volts is obtained, a malfunction of the HEI system unrelated to the DEFI system is indicated.
3. If reading is between .5 and 2.0 volts, the distributor is operating satisfactorily. Reconnect distributor electrical connector.
4. Disconnect blue ECM electrical connector and connect voltmeter between pin 2 of connector and ground. If a reading of less than .5, or more than 2.0 volts is obtained during engine cranking, check circuit 430 for open or short circuit.
5. If reading of .5-2.0 is obtained, circuit 430 is operating satisfactorily. Connect voltmeter between ECM connector pin 3 and ground to check for open circuit in circuit 453. If circuit 453 is satisfactory, replace ECM or connector.
6. After diagnosis and repairs have been completed, clear stored codes and road test vehicle.