Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Pinpoint Test B : Transmission Control Switch (TCS) Does Not Operate Properly
- Refer to Transmission Controls - Torqshift 6
for schematic and connector information.
Normal Operation and Fault Conditions
The TCS is a momentary contact switch located on the end of the selector lever. Pressing the TCS will engage or disengage the Tow/Haul function of the transmission, which delays upshifts to reduce the frequency of transmission shifting and provides engine braking to slow the vehicle and assist the driver in controlling the vehicle when descending a hill. When Tow/Haul is engaged, the Tow/Haul icon illuminates on the IPC. Each time the ignition switch is cycled, the PCM disengages the Tow/Haul operation regardless of the switch position the last time the engine was running.
DTC Fault Trigger Conditions
DTC Description Fault Trigger Condition PCM P1780:00 Transmission Control Switch (O/D Cancel) Circuit Out Of Self Test Range: No Sub Type Information This DTC can only set during the KOER on-demand self-test, and indicates the TCS circuit tested out of range. TCM P1780:00 Transmission Control Switch (O/D Cancel) Circuit Out Of Self Test Range: No Sub Type Information This DTC can only set during the KOER on-demand self-test, and indicates the TCS circuit tested out of range. Possible Sources
- Connectors damaged or pushed-out terminals, corrosion, loose wires and missing or damaged seals
- BCM fuse 19 (7.5A)
- TCS
- PCM
- TCM
- B1 RETRIEVE AND RECORD ALL DIAGNOSTIC TROUBLE CODES (DTCS)
- Using a diagnostic scan tool, carry out the KOEO and KOER PCM (gasoline engine vehicles) or TCM (diesel engine vehicles) self-test.
Is DTC P1780 present?
Yes GO to B2 No The TCS circuit is operating properly at this time. If the Tow/Haul lamp does not illuminate, REFER to: Information Center - Instrumentation, Message Center And Warning Chimes . - B2 CHECK THE TCS (TRANSMISSION CONTROL SWITCH) POWER CIRCUIT FOR VOLTAGE
- Ignition OFF.
- Disconnect Tow/Haul Switch C2399.
- Inspect for damaged or pushed-out terminals.
- Ignition ON.
- Measure:
Positive Lead Measurement / Action Negative Lead C2399-1 Ground
Is the voltage greater than 11 volts?
Yes GO to B3 No CHECK the BCM fuse 19 (7.5A). If the fuse is OK, REFER to OEM Wiring Diagrams to diagnose and repair the open circuit. If the fuse is not OK, REFER to OEM Wiring Diagrams to diagnose and repair the short to ground. - B3 CHECK THE TOW/HAUL SWITCH INPUT CIRCUIT FOR AN OPEN
- Disconnect PCM C175B (for vehicles equipped with a gasoline engine).
- Disconnect TCM C1750 (for vehicles equipped with a diesel engine).
- Inspect for damaged or pushed-out terminals.
- For vehicles equipped with a gasoline engine, measure:
Positive Lead Measurement / Action Negative Lead C2399-2 C175B-93
- For vehicles equipped with a diesel engine, measure:
Positive Lead Measurement / Action Negative Lead C2399-2 C1750-19
Is the resistance less than 3 ohms?
Yes GO to B4 No REPAIR the circuit. - B4 CHECK THE TOW/HAUL SWITCH
- Measure:
Positive Lead Measurement / Action Negative Lead
Tow/Haul switch component side, pin 1
Tow haul switch component side, pin 2
Is the resistance less than 3 ohms with the switch pressed, and greater than 10, 000 ohms with the switch released?
Yes GO to B5 No INSTALL a new selector lever, REFER to: Selector Lever . - Measure:
- B5 CHECK THE PCM OR TCM
- Connect BCM C2280B.
- Connect Tow/Haul Switch C2399.
- Ignition ON.
- For vehicles equipped with a gasoline engine, measure:
Positive Lead Measurement / Action Negative Lead C175B-93 Ground
- For vehicles equipped with a diesel engine, measure:
Positive Lead Measurement / Action Negative Lead C1750-19 Ground
Is the voltage greater than 11 volts with the switch pressed, and less than 5 volts with the switch released?
Yes For vehicles equipped with a gasoline engine, Refer to PCM Guided Routine . After installing a new PCM, CARRY OUT the transmission strategy download. REFER to: Transmission Strategy Download . For vehicles equipped with a diesel engine, INSTALL a new TCM. REFER to: Transmission Control Module (TCM) . CARRY OUT the transmission strategy download. REFER to: Transmission Strategy Download . No REPAIR the circuit.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.