ECM Code EO12: No Distributor (Tach) Signal: Action:

ECM turns on SERVICE ENGINE SOON light.

Possible causes of no distributor reference pulses are open pick-up coil, HEI module unable to process pick-up coil signals, or open or shorts on circuit No. 430 from module 5-wire connector to ECM.

Test Number 1)  This checks for proper voltage of HEI system. If voltmeter shows .5-2.8 volts, HEI is producing reference pulses.

Test Number 2)  This checks for proper ground connections between ECM and engine, and between ECM and HEI.

Test Number 3)  This checks for proper voltage through circuit No. 430 from HEI to ECM. If ECM terminal D8 sees .5-2.8 volts, then ECM is receiving reference pulses.

Test Number 4)  If HEI will produce spark, then fault is not within pick-up coil or module.