What causes GM code 12?

Normal marker flashed with key on and engine off during ALDL diagnosis Engine stalled or not cranking so no reference pulses reach the ECM Open or shorted distributor reference wire Failed distributor pickup coil or ignition module

How do I fix GM code 12?

Do not replace parts for code 12 alone with the engine off since it means diagnosis mode is active Retrieve codes with a paperclip across ALDL pins A and B and count Check Engine flashes Crank the engine and check for further codes if a no start is present Test distributor reference signal and wiring only if the engine will not start Clear codes by disconnecting battery power and recheck after a road test

12 No Distributor Reference Pulse

Q: What does GM code 12 mean?

GM code 12 — No Distributor Reference Pulse. Applies to 1982-1995 GM cars and C/K trucks, Camaro, Corvette.

Make: GM (1982-1995)
Category: Powertrain - Computer and Auxiliary Controls
Severity: Check Engine Light
Applies to: 1982-1995 GM cars and C/K trucks, Camaro, Corvette

How to read it

Code 12 reads as 1 flash, pause, 2 flashes on the check-engine light. Jump terminals A and B on the ALDL connector with the key off, then turn the key on with the engine off and count the check-engine flashes.

What does GM code 12 mean?

12 — No Distributor Reference Pulse. This code sets when your vehicle computer detects no distributor reference pulse.

Common causes of 12

Normal marker flashed with key on and engine off during ALDL diagnosis
Engine stalled or not cranking so no reference pulses reach the ECM
Open or shorted distributor reference wire
Failed distributor pickup coil or ignition module

How to fix 12

Do not replace parts for code 12 alone with the engine off since it means diagnosis mode is active
Retrieve codes with a paperclip across ALDL pins A and B and count Check Engine flashes
Crank the engine and check for further codes if a no start is present
Test distributor reference signal and wiring only if the engine will not start
Clear codes by disconnecting battery power and recheck after a road test