Chevrolet Silverado / GMC Sierra. Service manual — part 2495

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

1. Ignition ON, command the following ON and OFF with a scan tool. The respective turn

signal lamp should turn on and off.

LF Turn Signal

LR Turn Signal

RF Turn Signal

RR Turn Signal

If the turn signal lamp is always on or does not turn on, refer to Turn Signal Lamp
Circuit Malfunction below.

2. Ignition ON, operate the left and right turn signals from the multifunction/turn signal switch

and verify the left and right turn signal lamps and indicators operate normal.

If the left or right turn signals do not operate, refer to the Turn Signal Switch Circuit
Test below.

Circuit/System Testing

Turn Signal Lamp Circuit Malfunction

1. Ignition OFF, disconnect the X4 harness connector at the BCM.

2. Ignition ON, verify a test lamp illuminates between the following B+ terminals and ground.

B+ terminal 1

B+ terminal 2

B+ terminal 3

If the test lamp does not illuminate, test the B+ circuit for an open/high resistance. If
the circuit fuse is open, test the B+ circuit and the affected turn signal control circuits
for a short to ground.

3. Ignition OFF, connect the harness connector X4 harness connector at the BCM.

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Lighting - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

4. Disconnect the harness connector at the affected turn signal lamp.

5. Test for less than 1.0 ohms of resistance between the affected ground circuit terminal and

ground.

Front terminal G

Rear terminal GRD

Outside mirror terminal 10

If greater than the specified range, test the ground circuit for an open/high resistance.

6. Connect a test lamp between the affected turn signal control circuit terminal and ground.

Front terminal MIN

Rear terminal MJR

Outside mirror terminal 5

7. Ignition ON, command the affected turn signal on and off with a scan tool. The test lamp

should turn on and off when changing between the commanded states.

If the test lamp is always on, test the supply voltage circuit for a short to voltage. If the
circuit tests normal, replace the BCM.

If the test lamp is always off, test the supply voltage circuit for a short to ground or an
open/high resistance. If the circuit tests normal, replace the BCM.

8. If all circuits test normal, test or replace the appropriate turn signal bulb.

Turn Signal Switch Circuit Test

1. Ignition OFF, disconnect the harness connector 1 at the turn signal/multifunction switch.

2. Test for less than 1.0 ohm of resistance between the ground circuit terminal F and ground.

If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify the scan tool left and right turn signal parameters are Inactive.

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

Left terminal E

Right terminal D

4. Install a 3A fused jumper wire between the affected signal circuit terminal and the ground

circuit terminal F. Verify the scan tool left or right turn signal parameter is Active.

Left terminal E

Right terminal D

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

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Lighting - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

5. If all circuits test normal, test or replace the turn signal/multifunction switch.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Park/Turn Signal Lamp Bulb Replacement (Chevrolet) or Park/Turn Signal Lamp
Bulb Replacement (GMC)

Tail Lamp Bulb Replacement (GMC) or Tail Lamp Bulb Replacement (Chevrolet)

Turn Signal Multifunction Switch Replacement

Control Module References for BCM replacement, programming, and setup.

VANITY MIRROR LAMP 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 inadvertent power supply voltage circuit of the body control module (BCM) provides battery
positive voltage to each vanity mirror lamp. When the vanity mirror cover on the sunshade is
opened, a switch closes to provide a ground circuit and the vanity lamp illuminates.

Reference Information

Schematic Reference

Interior Lights Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Interior Lighting Systems Description and Operation

Electrical Information Reference

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Lighting - 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, fold down the sun visors and verify the vanity lamps illuminate.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at an affected vanity mirror lamp.

2. Test for less than 1 ohm of resistance between the ground circuit terminal B and ground.

If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify that a test lamp illuminates between the inadvertent power supply

circuit terminal A and ground.

If the test lamp does not illuminate, test the inadvertent power supply circuit for a
short to ground or an open/high resistance. If the circuit tests normal replace the BCM.

4. Connect the harness connector at the vanity mirror lamp, and remove the vanity lamp bulb.

5. Connect a test lamp across the bulb terminals

6. Ignition ON, open and close the vanity mirror. The test lamp should turn on and off when

changing between the commanded states.

If the test lamp is always on, replace the affected vanity mirror lamp.

If the test lamp is always off, replace the affected vanity mirror lamp.

7. If all circuits test normal, test or replace the affected vanity lamp bulb.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for BCM replacement, programming, and setup.

REPAIR INSTRUCTIONS

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Lighting - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado