Code 26, Quad-Driver CKT, (1 Of 3): Notes

Each PCM Quad-Driver 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, Code 26 will set.

Some QDM circuits will normally cycle between high and low, such as depressing brake pedal or 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 more than 30 seconds.

Fig 1: Code 26, Schematic, Quad-Driver Ckt, (VIN L)

Fig 2: Code 26, Schematic, Quad-Driver Ckt, (VIN 1)

NOTE: Test numbers refer to numbers on diagnostic chart.

PCM does not know which controlled circuit set Code 26, so this chart checks each circuit to determine which is at fault. On vehicles equipped with PCM-controlled hot light, this test checks hot light driver and hot light circuit.
QDM symptoms:
- Hot light always on, off during bulb check.
- Cooling fan always on low speed or will not come on at all.
- Poor driveability due to 100 percent canister purge.