C 3500 Truck 2WD V8-6.6L DSL Turbo VIN 1 (2002)
Transmission Mode Switch: Testing and Inspection
4L80-E/4L85-E Transmission
Tow/Haul Switch/Indicator Always On or Inoperative
Circuit Description
Tow/haul mode enables the operator to achieve enhanced shift performance when towing or hauling load. When tow/haul mode is selected, the
tow/haul switch input signal to the body control module (BCM) is momentarily toggled to zero volts. This signals the powertrain control module
(PCM) to extend the length of time between upshifts and increase transmission line pressure. Cycling the tow/haul switch again disables tow/haul
mode and returns the transmission to a normal shift pattern.
Diagnostic Aids
If the electrical circuit checks are OK and the tow/haul shift pattern is not occurring, there may be a mechanical/hydraulic condition that prevents
tow/haul operation. Refer to Symptoms - Automatic Transmission.
