Chevrolet Silverado / GMC Sierra. Service manual — part 2488

Electrical Information Reference

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, observe the scan tool hazard lamp switch parameter while operating the hazard
switch on and off. The reading should change between active and inactive.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector X1 at the turn signal/multifunction switch.

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

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

3. Ignition ON, verify the scan tool hazard lamp switch parameter is Inactive.

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

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

terminal C. Verify the scan tool hazard lamp switch parameter is 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, test or replace the turn signal/multifunction switch

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Turn Signal Multifunction Switch Replacement

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

HEADLAMPS MALFUNCTION

Diagnostic Instructions

2008 Chevrolet Silverado 1500

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

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.

Diagnostic Fault Information

Circuit/System Description

The low beam headlamps are controlled by the BCM through the headlamp low/HID relay, and
the high beams are controlled by the BCM through the high beam relay. Both relays are supplied
battery voltage and are energized when the BCM grounds the low side drive control circuits. The
headlamp on switch and high/low beam select switch signal circuits are referenced from battery
voltage by the BCM. When a switch is activated the signal circuit is grounded, and the BCM
determines the switch is active when the signal circuit voltage is low.

Reference Information

Schematic Reference

Headlights/Daytime Running Lights (DRL) Schematics

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Performance

Low Beam Hedalamp Control

1

1

3

-

High Beam Hedalamp Control

2

2

4

-

Low Beam Relay Control

3

1

B2575

-

High Beam Relay Control

5

2

B2580

-

Headlamp On Switch Signal

B257A

6

-

-

High/Low Beam Select
Switch Signal

5

2

-

-

Low Beam Headlamp Ground

-

2

-

-

High Beam Headlamp Ground

-

2

-

-

1. Low beam headlamps inoperative
2. High beam headlamps inoperative
3. Low beam headlamps always on
4. High beam headlamps always on
5. High beam headlamps always on with low beams
6. Manual headlamps inoperative

2008 Chevrolet Silverado 1500

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

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

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, observe the scan tool Headlamp Switch parameter while cycling the headlamp

switch between the auto and headlamp position. The parameter should cycle between Active
and Inactive.

If the parameter does not cycle between the specified values, refer to the Headlamp
Switch Circuit Test below.

2. Observe the headlamps while cycling the headlamp switch between the auto and headlamp

position. The low beam headlamps should turn on and off.

If 1 or both of the low beam headlamps do not turn on and off, refer to the Low Beam
Headlamp Circuit Test below.

3. Low beam headlamps ON, observe the scan tool High Beam Select Switch parameter while

switching the high/low beam select switch between the low and high beam positions. The
parameter should cycle between Active and Inactive.

If the parameter does not cycle between the specified values, refer to the High/Low
Beam Select Switch Circuit Test below.

4. Connect a test lamp between the relay side of a high beam headlamp fuse and ground.

5. Verify that the test lamp turns on and off while switching the high/low beam select switch

between the low and high beam positions.

2008 Chevrolet Silverado 1500

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

If the test lamp does not turn on and off while changing between the commanded
states, refer to the High Beam Relay Control Circuit Test below

6. If 1 or both of the high beam headlamps do not turn on and off, refer to the High Beam

Headlamp Circuit Test below.

Circuit/System Testing

Headlamp Switch Circuit Test

1. Ignition OFF, disconnect the harness connector at the headlamp switch.

2. Test for less than 1 ohm of resistance between the ground circuit terminal 8 and ground.

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

3. Ignition ON, verify the scan tool Headlamp Switch parameter is Inactive.

If not the specified value, test the signal circuit terminal 1 for a short to ground. If the
circuit tests normal, replace the BCM.

4. Install a 3A fused jumper wire between the signal circuit terminal 1 and the ground circuit

terminal 8. Verify the scan tool Headlamp Switch parameter is 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, test or replace the headlamp switch.

High/Low Beam Select Switch Circuit Test

1. Ignition OFF, disconnect the harness connector X2 at the turn signal/multifunction switch.

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

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

3. Ignition ON, verify the scan tool High Beam Select Switch parameter is Inactive.

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

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

terminal D. Verify the scan tool High Beam Select Switch parameter is 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, test or replace the signal/multifunction switch.

Low Beam Headlamp Circuit Test

2008 Chevrolet Silverado 1500

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