GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The headlamp leveling module receives inputs from the front and rear suspension position sensors to determine vehicle pitch. The suspension position sensors send an output to the headlamp leveling module as the vehicle suspension compresses and rebounds. The headlamp leveling module calculates the difference in vehicle pitch and sends a command to the headlamp leveling actuators. The headlamp leveling actuators drive the headlamps to the position commanded by the headlamp leveling module. The headlamp leveling module monitors the headlamp leveling actuator motor control circuits for proper circuit continuity and for shorts to ground or voltage. If a malfunction is detected, a DTC will be stored in memory.

DTC Descriptors

This diagnostic procedure supports the following DTC:

DTC B1458 AHLD Left Servo Driver Terminal 4 Circuit

The vehicle has DTCs including the DTC symptoms. Refer to DTC Symptom Description for more DTC symptoms.

DTC Symptom

DTC Symptom Descriptor

02

Short to Ground

05

Short to Battery or Open

Conditions for Running the DTC

The headlamp leveling module performs this diagnostic test mode every 0.8 millisecond when the following conditions are met:

    • The ignition is in the ON or CRANK position.
    • The headlamps are ON.

Conditions for Setting the DTC

DTC B1458 02

Will set when the headlamp leveling module detects a short to ground in the left headlamp leveling actuator motor 4 control circuit after 4 consecutive monitoring cycles.

DTC B1458 05

Will set when the headlamp leveling module detects an open or short to voltage in the left headlamp leveling actuator motor 4 control circuit after 4 consecutive monitoring cycles.

Action Taken When the DTC Sets

When DTC B1458 sets, the headlamp leveling module will disable all requests to both headlamp leveling actuators.

Conditions for Clearing the DTC

    • The condition responsible for setting the DTC no longer exists.
    • You issue a scan tool CLEAR DTCs command.
    • A history DTC will clear once 40 consecutive malfunction free ignition cycles have occurred.

Diagnostic Aids

Thoroughly inspect the wiring and connectors. An incomplete inspection of the wiring and connectors may result in misdiagnosis causing part replacement with the reappearance of the malfunction. If an intermittent malfunction exists, refer to Testing for Intermittent Conditions and Poor Connections .

Step

Action

Yes

No

Schematic Reference: Headlight Leveling Schematics

Connector End View Reference: Lighting Systems Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Is DTC B1458 02 present?

Go to Step 3

Go to Step 6

3

Test the left headlamp leveling motor 4 circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 13

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Disconnect the left headlamp leveling actuator harness connector.
  3. Connect a 4-amp fused jumper between the left headlamp leveling motor 3 circuit and the left headlamp leveling motor low reference circuit at the left headlamp leveling actuator harness connector.
  4. Turn ON the ignition, with the engine OFF.
  5. Turn ON the headlamps.
  6. With a scan tool, request the headlamp leveling module DTC display.

Does the scan tool indicate DTC B1458 02 is current?

Go to Step 5

Go to Step 9

5

Test the left headlamp leveling motor low reference circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 13

Go to Step 10

6

Test the left headlamp leveling motor 4 circuit for an open or short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 13

Go to Step 7

7

  1. Turn OFF the ignition.
  2. Disconnect the left headlamp leveling actuator harness connector.
  3. Connect a 3-amp fused jumper between the left headlamp leveling motor 4 circuit and the left headlamp leveling motor low reference circuit at the left headlamp leveling actuator harness connector.
  4. Ignition ON, with the engine OFF.
  5. Turn ON the headlamps.
  6. With a scan tool, request the headlamp leveling module DTC display.

Does the scan tool indicate DTC B1458 05 as current?

Go to Step 8

Go to Step 9

8

Test the left headlamp leveling motor low reference circuit for an open or short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 13

Go to Step 10

9

Inspect for poor connections at the harness connector of the headlamp leveling control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 13

Go to Step 12

10

Inspect for poor connections at the harness connector of the left headlamp leveling actuator. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 13

Go to Step 11

11

Replace the left headlamp leveling actuator. Refer to Headlamp Leveling Module Replacement .

Did you complete the replacement?

Go to Step 13

--

12

Replace the headlamp leveling control module. Refer to Control Module References 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