Q: Torque converter goes in/out of lock up at cruising speed

asked by on August 08, 2016

My SUV’s torque converter goes in and out of lock up when going a steady cruising speed. While driving a constant 65 mph, on level ground, the engine RPMs will go from 1700 to 2000 and then back again. It acts as if it is hunting between gears; however, the transmission is in top gear. Can you give me ideas of how to solve this problem?

Thanks for writing in about your 1999 Chevrolet Suburban. There are DTCs (diagnostic trouble codes) that will indicate faults with TCC solenoid and brake pedal switch circuits. A scan tool can be used to observe brake pedal switch position while driving to determine if this is the input causing the TCC to disengage. The state of command to the TCC solenoid can also be monitored during test drive to help diagnose the rough cruising speed acceleration.

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