With RPO Code X88, Z75, and Z88
DTC B2600 (With X88, Z75, and Z88)
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.
DTC Descriptor
DTC B2600 00
- Daytime Running Lamp Control Circuit
Diagnostic Fault Information
Circuit/System Description
The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 0.2 and 4.9 V depending on outside lighting conditions. The body control module (BCM) provides a 5 V reference signal to the ambient light sensor. The body control module (BCM) monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights (DRL) or automatic lamp control (ALC) when the headlamp switch is in the AUTO position. In daylight conditions, the BCM will command the DRLs ON by applying ground to the DRL relay via the DRL relay control circuit. When the BCM applies ground to the DRL relay control circuit, the DRL relay coil energizes causing the relay switch contacts to close. With the DRL relay energized, voltage is applied through the relay switch contacts, the DRL Resistor, and the DRL fuse to the left and right low beam headlamp fuses illuminating the low beam headlamps. Any function or condition that turns the headlamps ON will cancel DRL operation. Any function or condition that turns on the headlamps will cancel DRL operation.
Conditions for Running the DTC
* Battery voltage must be between 9-16 V.
* Headlamp switch in AUTO position.
Conditions for Setting the DTC
The BCM detects a short to voltage in the DRL relay control circuit.
Action Taken When the DTC Sets
The BCM will disable the DRL relay control circuit.
Conditions for Clearing the DTC
* The condition responsible for setting the DTC no longer exists.
* A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.
Reference Information
Schematic Reference
Headlights/Daytime Running Lights (DRL) Schematics (Headlights/Daytime Running Lights (DRL) Schematics)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Exterior Lighting Systems Description and Operation (Exterior Lighting Systems Description and Operation)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Testing
Warning
The high intensity discharge system produces high voltage and current. To reduce the risk of severe shocks and burns:
* Never open the high intensity discharge system ballast or the arc tube assembly starter.
* Never probe between the high intensity discharge system ballast output connector and the arc tube assembly.
1. Ignition OFF, disconnect the X4 harness connector at the fuse block - underhood.
2. Connect a test lamp between the control circuit terminal H4 and B+.
3. Command the DRLs 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 control circuit for a short to ground. If the circuit tests normal, replace the BCM.
• If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
4. Ignition OFF, connect the X4 harness connector at the fuse block - underhood. Disconnect the harness connector at the daytime running lamp.
5. Test for less than 5 ohm between the daytime running lamp ground circuit terminal listed below and ground:
* With X88 - Terminal C
* With Z75 and Z88 - Terminal B
• If greater than the specified range, test the ground circuit for an open/high resistance.
6. Connect a test lamp between control circuit terminal A and ground:
7. Command the DRLs 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 control circuit for a short to voltage. If the circuit tests normal, replace the fuse block - underhood.
• If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the fuse block - underhood.
• If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the daytime running lamp.
8. If all circuits test normal, test or replace the daytime running lamp.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Headlamp Replacement (Cadillac Escalade) (Headlamp Replacement (Cadillac Escalade))Headlamp Replacement (GMC Yukon Two-mode Hybrid) (Headlamp Replacement (GMC Yukon Two-mode Hybrid))Headlamp Replacement (Yukon) (Headlamp Replacement (Yukon))Headlamp Replacement (Chevrolet Tahoe Two-mode Hybrid) (Headlamp Replacement (Chevrolet Tahoe Two-mode Hybrid))Headlamp Replacement (Tahoe, Avalanche) (Headlamp Replacement (Tahoe, Avalanche))Headlamp Replacement (Escalade PLATINUM) (Headlamp Replacement (Escalade Platinum))Headlamp Replacement (Non HID) (Headlamp Replacement (Non HID))
* Underhood Electrical Center or Junction Block Replacement (Underhood Electrical Center or Junction Block Replacement)
* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming