GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 CTS 🢒 DTC 🢒 DTC B3420

Circuit Description

The headlamp leveling sensor rear provides the headlamp leveling control modules with rear axle position information. The headlamp leveling switch bit 1 signal circuit is shared between the 2 headlamp leveling control modules. The sensor is permanently grounded and has battery voltage supplied with the ignition in the ON position. The sensor arm is connected to the control arm of the rear suspension. As the vehicle travels the suspension compresses and rebounds moving the headlamp leveling sensor rear arm. This causes the signal output of the sensor to change. The headlamp leveling control modules then compares this information with the headlamp leveling sensor front information and adjusts the headlamp leveling accordingly.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B3420 AHLD Rear Axle Sensor Signal Circuit

Conditions for Running the DTC

Each of the headlamp leveling control modules run the DTC every 40 milliseconds when the follow conditions are met:

    • The ignition is ON.
    • The headlamps are ON.

Conditions for Setting the DTC

Each time the DTC is ran and a fault is detected an internal counter in each of the headlamp leveling control modules is increased by one. When the counter reaches 5 the DTC is set as current.

Action Taken When the DTC Sets

The headlamp leveling control module uses an internal offset of the headlamp leveling sensor front in order to keep the leveling system active.

Conditions for Clearing the DTC

Each time the DTC is ran and a fault is not detected the counter is decreased by one until the counter reaches 0.

Test Description

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

  1. This step determines the proper diagnostic path for the DTC.

    2.

  2. This step tests for battery voltage at the headlamp leveling sensor rear.

    3.

  3. This step tests for an open in the headlamp leveling sensor rear ground circuit.

    4.

  4. This step tests for both a short to ground and a short to battery voltage.

    5.

  5. This step tests for an open or high resistance between the headlamp leveling sensor rear and the headlamp leveling control module that has the DTC present.

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 in Vehicle DTC Information

2
  1. Connect a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Turn ON the headlamps.
  4. Select the display DTC function for both headlamp leveling control modules for DTCs.

Is the DTC B3420 a current DTC?

Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

3

Is the DTC B3420 current in both the right and left headlamp leveling control modules?

Go to Step 4

Go to Step 7

4

  1. Turn OFF the ignition.
  2. Connect a test lamp between the ignition 1 voltage circuit of the headlamp leveling sensor rear and a good ground.
  3. Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

Go to Step 5

Go to Step 10

5

Connect a test lamp between the ignition 1 voltage circuit of the headlamp leveling sensor rear and the ground circuit of the headlamp leveling sensor rear.

Does the test lamp illuminate?

Go to Step 6

Go to Step 11

6

Test the headlamp leveling switch bit 1 signal circuit for an open, short to voltage, short to ground or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 8

7

Test the headlamp leveling switch bit 1 signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 9

8

Inspect for poor connections at the harness connector of the headlamp leveling sensor rear. 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 14

Go to Step 12

9

Inspect for poor connections at the harness connector of the appropriate headlamp leveling control module. 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 14

Go to Step 13

10

Repair the open or high resistance in the ignition 1 voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 14

--

11

Repair the open or high resistance in the ground circuit of the headlamp leveling sensor rear. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 14

--

12

Important: Perform the calibration procedure for both headlamp leveling modules. Refer to Headlamp Leveling Module Programming and Setup .

Replace the headlamp leveling sensor rear. Refer to Headlamp Leveling Rear Suspension Height Sensor Replacement .

Did you complete the replacement?

Go to Step 14

--

13

Important: Perform the calibration procedure for the appropriate headlamp leveling module. Refer to Headlamp Leveling Module Programming and Setup .

Replace the appropriate headlamp leveling control module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 14

--

14
  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 test.

Does the DTC reset?

Go to Step 2

System OK