Chevrolet Silverado / GMC Sierra. Service manual — part 1315

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Ignition ON, perform the IPC display test using a scan tool. Verify the indicator illuminates and
turns OFF.

If the indicator does not operate as expected during this test, replace the IPC.

If the indicator functions normally during this test, replace the ECM/PCM.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for ECM, PCM or IPC replacement, setup and programming

CRUISE CONTROL MALFUNCTION

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

The body control module (BCM) supplies battery voltage to the cruise control switch. The cruise
control switch signal is an input to the BCM. The BCM monitors the cruise control switch signal
circuit in order to detect when the driver has requested to perform a cruise control function. The
BCM detects a specific voltage signal on the cruise control switch signal circuit when a switch is
applied.

Conditions for Enabling Cruise Control

The vehicle speed is greater than 40 km/h (25 mph).

The vehicle is not in PARK, REVERSE, NEUTRAL, or 1st gear.

2008 Chevrolet Silverado 1500

2008 ENGINE Cruise Control - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

The system voltage is within 9-16 volts.

The park brake or brakes are not applied.

Diagnostic Aids

In order to avoid misdiagnosis, inspect for the following:

Verify there are no DTCs set as current. If any DTCs are set as current, refer to Diagnostic
Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostics/repairs
before proceeding with symptom based diagnostics.

Inspect the cruise control switches for any sticking or binding conditions.

Inspect for proper operation of the stop lamps. Refer to Exterior Lighting Systems
Description and Operation .

With the ignition ON, rotate the steering wheel to both steering stops while activating each
cruise control switch separately. With a scan tool, observe all cruise control switch
parameters in the BCM. Ensure that each cruise control switch activates and that each of the
displayed switch position parameters match the currently activated switch, and do not read
Error. This may aid in locating an intermittent fault within the inflatable restraint steering
wheel module coil.

Reference Information

Schematic Reference

Cruise Control Schematics

Steering Wheel Secondary/Configurable Control Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Cruise Control Description and Operation

Electrical Information Reference

IMPORTANT: Repair any brake system related symptoms and DTCs before

performing this diagnostic.

2008 Chevrolet Silverado 1500

2008 ENGINE Cruise Control - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Ignition ON, cruise on/off switch ON. With a scan tool, observe the scan tool Cruise Control
Switch parameter in the BCM. While pressing each of the cruise control switches, the scan tool
display should change to display the current switch being actuated. Road test the vehicle to ensure
the cruise control system functions as described in Cruise Control Description and Operation.

Circuit/System Testing

1. Ignition OFF, remove the inflatable restraint steering wheel module. Refer to Inflatable

Restraint Steering Wheel Module Replacement .

2. Disconnect the harness connector at the cruise control switch.

3. Ignition ON, test for B+ between the supply circuit terminal 1 and ground.

If less than the specified range, test the supply circuit for a short to ground or an
open/high resistance. If the circuit tests normal, replace the BCM.

4. Verify the scan tool Cruise Control Switch parameter is OFF.

If not the specified value, test the signal circuit terminal 3 for a short to voltage. If the
circuit tests normal, replace the BCM.

5. Ignition OFF, connect the harness connector at the cruise control switch.

6. Ignition ON, cruise control switch ON, observe the scan tool Cruise Control Switch

parameter. The parameter should display ON.

If not the specified value, test the signal circuit terminal 3 for a short to ground or an
open/high resistance. If the circuit tests normal, test or replace the cruise control
switch.

7. Observe the scan tool Cruise Control Switch parameter while pressing the RES + portion of

the cruise control switch. The parameter should display Resume.

If not the specified value, test or replace the cruise control switch.

8. Observe the scan tool Cruise Control Switch parameter while pressing the SET - portion of

2008 Chevrolet Silverado 1500

2008 ENGINE Cruise Control - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

the cruise control switch. The parameter should display Set.

If not the specified value, test or replace the cruise control switch.

9. Observe the scan tool Cruise Control Switch parameter while pressing the Cancel portion of

the cruise control switch. The parameter should display Cancel.

If not the specified value, test or replace the cruise control switch.

10. If all circuits and the component test normal, replace the BCM.

Component Testing

1. With the ignition OFF, remove the inflatable restraint steering wheel module. Refer to

Inflatable Restraint Steering Wheel Module Replacement .

2. Remove the steering wheel cruise control switch. Refer to Steering Wheel Control Switch

Assembly Replacement .

3. Connect a DMM between terminals 1 and 3 of the cruise control switch. Cruise control

ON/OFF switch ON, measure the resistance while individually activating and holding each
cruise control function switch and compare the resistance reading to the values in the table
for the appropriate switch.

If any of the resistance measurements for the individual switches are not within the
listed resistance values, replace the cruise control switch assembly.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Steering Wheel Control Switch Assembly Replacement

Control Module References for BCM replacement, setup, and programming

IMPORTANT: The cruise control switch must be ON in order to properly

measure the resistance of the - /SET, the +/RES, and the Cancel
switches.

Function Switch

Minimum Resistance

Value

Maximum Resistance

Value

OFF

O.L.

O.L.

ON

6.6k Ohms

7.0k Ohms

-/SET

2.1k Ohms

2.5k Ohms

+/RES

3.6k Ohms

4.0k Ohms

Cancel

1.3k Ohms

1.7k Ohms

2008 Chevrolet Silverado 1500

2008 ENGINE Cruise Control - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado