Vehicle: 2008 Chevrolet Suburban K1500, 5.3-L

Complaint

In this situation, the customer complained that the vehicle’s miles per gallon drastically decreased, the cruise control became unresponsive and the check engine light illuminated.

Diagnosis

Connecting a scan tool shows code P0573 – Brake Switch “A” Circuit High. Performing a road test, and attempting to activate the cruise control confirmed the customer’s concern that the cruise control did not operate. Continuing the road test with a scan tool to monitor live data found the torque converter clutch (TCC) was never commanded on while driving.

Continuing to monitor live data on the scan tool, and repeatedly depressing the brake pedal, found that the brake light switch status parameter never changed state. After and inspection of the brake light switch circuits, no faults were found in the wiring harness or connectors.

Disconnecting the brake light switch, and visually inspecting the connector and pins, uncovered no defects. Using a multimeter to check for the presence of continuity through the switch, and depressing the brake pedal, found the switch had no continuity. It was determined that the defective brake light switch had prevented the TCC from being commanded on, which resulted in the vehicle’s poor fuel economy.

Correction

Replaced the brake light switch, cleared codes, performed a road test and verified the vehicle operated properly. The check engine light did not illuminate and no fault codes returned.

Courtesy of Mitchell 1’s SureTrack Real Fixes. For more, visit mitchell1.com.