Part 1 of 3

Code 26 Chart, Part 1 Of 3.:

Code 26 Wiring Diagram:

CIRCUIT DESCRIPTION:

The ECM is used to control several components such as those illustrated above. The ECM controls a device by turning "ON" or "OFF" a device called a quad-driver. The ECM also monitors the state of each of the control circuits by way of the fault line. When the ECM is not turning "ON" the circuit being controlled, there should be 12 volts present on the fault line. If 12 volts is not present due to an open or shorted control circuit, or an open component coil, a failure will be logged in memory. Also when the ECM is commanding the component "ON" the control circuit should be low (near 0 volts).

If the fault line does not sense the low state, a failure will be logged. This could be caused by a short to 12 volts on the control circuit by a shorted component or by a faulty ECM driver.



NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to ECM CONNECTOR IDENTIFICATION under ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS for correct color code identification of circuit.


TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. The ECM does not know which controlled circuit caused the Code 26 so this chart will go through each of the circuits to determine which is at fault. An EGR circuit problem should also set a Code 32 but after that problem is fixed this chart should be performed.

2. This test checks the "SERVICE ENGINE SOON" light driver and the "SERVICE ENGINE SOON" light circuit.


3. QDM symptoms:

^ Cooling fan(s) inoperative
^ Poor driveability due to 100% canister purge.
^ Coolant light "ON" all the time, "OFF" during bulb check.
^ EGR inoperative - Code 32.
^ TCC inoperative