E012

TEST CONDITIONS:
1. Code EO41 not set;
2. Code EO12 is tested any time cam sensor signals are being received.

FAILURE CONDITIONS:
If the ECM does not receive distributor reference pulses for 8 seconds with cam reference pulses being received, Code EO12 will set.

ACTION TAKEN:
1. ECM turns on "Engine Control System Fault" telltale;
2. ECM commands BCM to display "Service Now" message on Driver Information Center (DIC).

DESCRIPTION
Possible causes of "no distributor reference signal" are:
1. Open or shorts on CKT 430 and 453 from distributor module to ECM;
2. Open pick-up coil - the pick-up coil produces a signal that the HEI module uses to produce distributor reference pulses;
3. HEI module unable to process pick-up coil signals to produce distributor reference pulses.

Notes on Fault Tree:
1. Checking for proper output of HEI system. If voltmeter reads 0.5-2.8 volts, HEI module is receiving pick-up coil signal and producing reference pulses.
2. Checking for proper ground at the ECM and HEI module.
3. Checking for reference pulses on CKT 430 from the HEI module to the ECM. If ECM terminal D8 has 0.5-2.8 volts, then the ECM is receiving reference pulses.
4. Checking for HEI module operation. If the HEI module will produce spark, then the fault is not the pick-up coil or HEI module.

Notes on Intermittents:
If Code EO12 is stored as a history code, start the engine and allow to idle while manipulating CKT 430 and 453. An intermittent open will cause the engine to stumble or quit when the ECM loses distributor reference signals. If the wiring and ECM connectors are OK, check the HEI pick-up coil leads for an intermittent open circuit. See HEI Diagnosis.