Code 26, Quad-Driver CKT: Notes

Each PCM Quad-Driver Module (QDM) has a fault line which is monitored by PCM. PCM compares voltage values of fault line with acceptable values in PCM memory. If PCM senses values other than accepted values, a Code 26 will set.

Some QDM circuits will normally cycle between high and low, such as depressing brake pedal. Some "Scan" testers may set a false Code 26 if engine is running, tester is installed and brake pedal is depressed for more than 30 seconds.

1. PCM does not know which controlled circuit set Code 26, so this chart checks each circuit to determine which is at fault. This step tests SERVICE ENGINE SOON light driver and circuit.

   QDM Symptoms:

   • Cooling fan always on low speed or will not come on at all.
   • Poor driveability due to 100 percent canister purge.
     NOTE: Test number refers to number on diagnostic chart.
2. This determines which circuit is out of specification. All terminals except GD16 and GD15 should have battery voltage with ignition on, engine not running and ALDL test terminal not grounded.
3. This determines if problem is circuit or component. Factory-installed PCM has an internal fuse and is unlikely to need replacement.