Code 26: Quad-Driver Circuit: Notes

Each ECM Quad-Driver has a fault line which is monitored by the ECM. The ECM compares voltage values of the fault line with acceptable values in ECM memory. If the ECM senses other than accepted values, a Code 26 will set.

Some QDM circuits will normally cycle between high and low, such as depressing the brake pedal, cooling fans cycling on and off. QDM 2 will not set a Code 26. 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.

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

The ECM does not know which controlled circuit set the Code 26. This tests SERVICE ENGINE SOON light driver and circuit.
QDM SYMPTOMS
- TCC inoperative, Code 39
- EGR inoperative, Codes 63, 64 and 65.
- Hot light on all the time, off during bulb check.
- Cooling fan on low speed all of the time or will not come on at all.
- Poor driveability due to 100 percent canister purge.