Diagnostic Procedure ("L"&"M" Series)

NOTE: For circuit identification, see CONNECTOR IDENTIFICATION and Fig 1.

Install a scan tool. Turn ignition on, engine off. Cycle the tow/haul switch while observing TOW/HAUL MODE on the scan tool. Does the scan tool display ACTIVE when the switch is first pressed, and then INACTIVE when the switch is pressed again? If so, see DIAGNOSTIC AIDS . If not, go to next step.

NOTE: The tow/haul switch is connected to the steering column harness.

Disconnect the instrument panel wiring harness connector (C201) from the tow/haul switch. Install a fused jumper wire between instrument panel wiring harness connector (C201) terminals A9 and A8. Does the scan tool TOW/HAUL MODE indicate a status change? If so, go to step 7. If not, go to next step.
Measure the voltage at instrument panel wiring harness connector (C201) terminal A9. Is ignition voltage measured? If so, go to step 6. If not, go to next step.
Measure the voltage at BCM connector C1 terminal B12. Is ignition voltage measured? If so, go to next step. If not, go to step 8.
Test the tow/haul switch signal circuit (553) for an open or shorted condition. Did you find and correct the condition? If so, go to step 9. If not, see DIAGNOSTIC AIDS .
Test the tow/haul switch ground circuit (750) for an open or shorted condition. Did you find and correct the condition? If so, go to step 9. If not, see DIAGNOSTIC AIDS .
Replace the tow/haul switch. Did you complete the replacement? If so, go to step 9.
Test the BCM for proper operation. See appropriate BODY CONTROL MODULES article. Did you find and correct the condition? If so, go to next step.
After the repair is complete, observe TOW/HAUL MODE on the scan tool display, while cycling the tow/haul switch. Does the scan tool display ACTIVE when the switch is first pressed, and then INACTIVE when the switch is pressed again? If so, system is okay. If not, go to step 1.

Fig 1: Tow/Haul Mode System Wiring Diagram ("L" & "M" Series)

Courtesy of GENERAL MOTORS CORP.