GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Blazer - 2WD 🢒 Body 🢒 Lighting Systems 🢒 DTC B2618

Circuit Description

The body control module (BCM) controls the ground of the courtesy lamp relay on the courtesy lamp relay coil control circuit. When the BCM receives a signal from a door jamb switch, a signal to unlock the doors from the remote control door lock module receiver module or the dome lamp switch being turned ON, the BCM grounds the relay and turns ON the courtesy lamps.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2618 Passenger Compartment Dimming 2 Circuit High

Conditions for Running the DTC
    • The system voltage must be between 9-16 volts.
    • The ignition switch in the OFF position.
    • Unlock doors from the remote control door lock key fob, or open any door, or turn ON the dome lamp from the headlamp switch thumbwheel.
    • The above conditions must be met for more than 0.5 seconds.

Conditions for Setting the DTC

To set B2618, the following conditions must be present:

    • Courtesy lamps ON.
    • The courtesy lamp relay coil control circuit is shorted to battery voltage.
    • The above conditions must be met for 0.5 seconds.

Action Taken When the DTC Sets

The courtesy lights will not function.

Conditions for Clearing the MIL/DTC
    • This DTC will clear after a fault free courtesy lamp operation.
    • A history DTC will clear after 100 consecutive ignition cycles without a fault present.
    • Use a scan tool in order to clear history and current DTCs.

Diagnostic Aids

       Important: Use the appropriate probe from the J 35616 Connector Test Adapter Kit for any probing of the electrical components in this table, in order to avoid damage to the terminals.

    • The scan tool must display DTC B2618 as a current code before performing these diagnostics.
    • Perform a visual inspection for loose or poor connections at all related components. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Listen for an audible click when the courtesy lamp relay operates. Command both the ON and OFF states. Repeat the commands as necessary.

    2.

  2. This step tests for voltage at the coil side of the courtesy lamp relay. The CTSY LP fuse supplies power to the coil side of the courtesy lamp relay.

    3.

  3. This step verifies that the BCM is providing ground to the courtesy lamp relay.

    4.

  4. This step tests if ground is constantly being applied to the courtesy lamp relay.

    5.

  5. After replacement of the BCM you must calibrate the new module for proper operation.

Step

Action

Yes

No

Schematic Reference: Interior Lights Schematics

Connector End View Reference: Lighting Systems Connector End Views or Computer/Integrating Systems Connector End Views in Computer/Integrating Systems

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the courtesy lamp relay ON and OFF.

Does the courtesy lamp relay turn ON and OFF with each command?

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the courtesy lamp relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the coil side supply circuit of the courtesy lamp relay with a test lamp that is connected to a good ground. Refer to Electrical Center Identification Views in Wiring Systems.

Does the test lamp illuminate?

Go to Step 4

Go to Step 10

4

  1. Connect a test lamp between the control circuit of the courtesy lamp relay and the coil side supply circuit of the courtesy lamp relay. Refer to Electrical Center Identification Views in Wiring Systems.
  2. With a scan tool, command the courtesy lamp relay ON and OFF .

Does the test lamp turn ON and OFF with each command?

Go to Step 8

Go to Step 5

5

Does the test lamp remain illuminated with each command?

Go to Step 7

Go to Step 6

6

Test the control circuit of the courtesy lamp relay for a short to voltage or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

7

Test the control circuit of the courtesy lamp relay for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

8

Inspect for poor connections at the courtesy lamp relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 11

9

Inspect for poor connections at the harness connector of the body control module (BCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 12

10

Repair the coil side supply circuit of the courtesy lamp relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 13

--

11

Replace the courtesy lamp relay. Refer to Relay Replacement in Wiring Systems.

Did you complete the replacement?

Go to Step 13

--

12

Replace the BCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 13

--

13
  1. Use the scan tool in order to clear the DTCs .
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK