Chevrolet Silverado / GMC Sierra. Manual

ground while monitoring the scan tool TR
Sw. A/B/C/P parameter.
When signal circuit A is grounded, do any
other signal circuits indicate LOW?

Go to Step 12 Go to Step 7

Connect a fused jumper wire from the TR
switch connector, signal circuit B, to
ground while monitoring the scan tool TR
Sw. A/B/C/P parameter.
When signal circuit B is grounded, do any
other signal circuits indicate LOW?

Go to Step 12 Go to Step 8

Connect a fused jumper wire from the TR
switch connector, signal circuit C, to
ground while monitoring the scan tool TR
Sw. A/B/C/P parameter.
When signal circuit C is grounded, do any
other signal circuits indicate LOW?

Go to Step 12 Go to Step 9

Connect a fused jumper wire from the TR
switch connector, signal circuit P, to
ground while monitoring the scan tool TR
Sw. A/B/C/P parameter.
When signal circuit P is grounded, do any
other signal circuits indicate LOW?

Go to Step 12

Go to Step

Test the signal circuits of the TR switch
that did not indicate HI for a short to
ground.
Refer to Testing for Short to Ground
and Wiring Repairs .
Did you find and correct the condition?

Go to Step 17

Go to Step

Test the signal circuits of the TR switch
that did not indicate proper voltage for an
open.
Refer to Testing for Continuity and
Wiring Repairs .
Did you find and correct the condition?

Go to Step 17

Go to Step

Test the affected signal circuits of the TR
switch for a shorted together condition.
Refer to Circuit Testing and Wiring
Repairs .
Did you find and correct the condition?

Go to Step 17

Go to Step

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

TOW/HAUL SWITCH/INDICATOR ALWAYS ON OR INOPERATIVE

DIAGNOSTIC INSTRUCTIONS

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

CIRCUIT/SYSTEM DESCRIPTION

Tow/haul mode enables the operator to achieve enhanced shift performance when towing or

Test the ground circuit of the TR switch
for an open.
Refer to Testing for Continuity and
Wiring Repairs .
Did you find and correct the condition?

Go to Step 17

Go to Step

Replace the TR switch, this switch is part
of the park/neutral position switch.
Refer to Park/Neutral Position Switch
Replacement.
Did you complete the replacement?

Go to Step 17

Replace the TCM.
Refer to Control Module References for
replacement, setup, and programming.
Did you complete the replacement?

Go to Step 17

Replace the IPC.
Refer to Control Module References for
replacement, setup, and programming.
Did you complete the replacement?

Go to Step 17 Go to Step 2

1. Turn ON the ignition, with the

engine OFF.

2. With the scan tool, observe the TR

Sw. display while selecting each
transmission range: P, R, N, D4, D3,
D2 and D1.

Does each selected transmission range
match the scan tool TR Sw. display?

System OK Go to Step 2

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

hauling a 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 transmission control
module (TCM) 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. The tow/haul switch is a momentary switch and is normally open. The
internal spring in the switch will always cause the switch state to return to open when not held in
to the closed position.

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.

REFERENCE INFORMATION

Schematic Reference

Automatic Transmission Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Transmission Control Module Scan Tool Information (4L60-E) or Transmission Control
Module Scan Tool Information (6L50/6L80/6L90)

CIRCUIT/SYSTEM VERIFICATION

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

With a scan tool observe the Tow/Haul switch parameter. Operate the Tow/Haul switch several
times, and observe the parameter as you operate the switch with the transmission in DRIVE. The
parameter should toggle between ACTIVE and INACTIVE when the switch is operated.

CIRCUIT/SYSTEM TESTING

1. Ignition OFF, transmission in PARK or NEUTRAL, disconnect the Tow/Haul switch

connector.

2. Test for less than 1 ohm of resistance between the Tow/Haul switch signal circuit terminal B

and ground.

If greater than the specified range, test the ground circuit for an Open/High resistance.

3. Ignition ON, verify the scan tool parameter Park/Neutral displays INACTIVE.

If not the specified value, test the signal circuit for a short to ground. If the circuit tests
normal, replace the BCM.

4. Install a fused jumper between the signal circuit and ground. Verify the scan tool parameter

displays ACTIVE.

If not the specified value, test the signal circuit for a short to voltage or an open/high
resistance. If the circuit tests normal, replace the BCM.

5. If all circuits test normal, replace the Tow/Haul switch.

COMPONENT TESTING

1. Ignition OFF, transmission in PARK or NEUTRAL, disconnect the transmission Tow/Haul

switch assembly.

2. Test for infinite resistance between the Tow/Haul switch with the switch in the OPEN

position.

If not the specified value, test the signal circuit for a short to voltage or an open/high
resistance. If the circuit tests normal, replace the Tow/Haul switch assembly.

REPAIR PROCEDURES

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Body Control Module (BCM) assembly replacement. Refer to Control Module
References for BCM replacement, setup, and programming

Perform the Shift Lever Replacement.

TRANSMISSION FLUID CHECK

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

Content .. 1009 1010 1011 1012 ..

Chevrolet Silverado / GMC Sierra. Manual - part 1011