Code 12 - No Distributor Reference Pulse To ECM

CAUTION: The distributor provides a tach signal to the ECM through a filter indicating engine RPM. Tachometer must only be connected to the distributor side of filter.

NOTE: Test numbers refer to test numbers on diagnostic chart.

1. This step checks for a poor connection at tach filter wire connector as the source of no distributor reference pulse. Check for corrosion on terminal, terminal not fully seated, or terminal not properly attached to wire. Terminal must be removed and inspected.
2. This step determines if a reference pulse voltage is being sent to ECM. Normal voltage should be over one volt. Check for good terminal contact at ECM terminal No. 19.
3. This step checks voltage from distributor through tach filter. Voltage should be above 10 volts.
4. This step checks voltage from distributor. Voltage reading should be above 10 volts.

Fig 1: Code 12, No Distributor Reference Pulse to ECM Flow Chart & Schematic

Fig 2: Code 12, No Distributor Reference Pulse to ECM Flow CharT