For 1990-2009 cars

### Circuit Description

The rear suspension position sensor provides the headlamp level controller with rear suspension position information. The sensor is permanently grounded and has voltage supplied with the ignition in the ON or CRANK 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 suspension position sensor arm. This causes the signal output of the sensor to change. The headlamp level controller compares this information with the front suspension position sensor information and adjusts the headlamp leveling as needed. For more detailed information concerning headlamp leveling operation, refer to Exterior Lighting Systems Description and Operation .

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B3420 AHLD Rear Axle Sensor Signal 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
03 | Voltage Below Threshold
07 | Voltage Above Threshold

### Conditions for Running the DTC

The headlamp level controller performs this diagnostic test mode every 3.2 milliseconds 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 B3420 will set when one of the following conditions occur:

#### DTC B3420 02

The rear suspension position sensor voltage reference is less than 4.49 volts for 9.6 milliseconds.

#### DTC B3420 03

The rear suspension position sensor voltage reference is less than 0.5 volt for 9.6 milliseconds.

#### DTC B3420 07

The rear suspension position sensor voltage reference is 4.5 volts or greater for 9.6 milliseconds.

### Action Taken When the DTC Sets

For DTC B3420 02, the following actions are taken:

• | The headlamp level controller will turn OFF power to the rear suspension position sensor and wait 10 seconds before reapplying power to the sensor. If the reference voltage is less than 4.49 volts, the headlamp level controller will conclude a rear suspension position sensor failure has occurred.

• | The headlamp level controller will disable the rear suspension position sensor.

For DTC B3420 03 and B3420 07, the following actions are taken:

• | If the headlamp leveling actuator has positioned the headlamps above the nominal level, the headlamp level controller will drive the headlamps to the nominal setting.

• | If the headlamp leveling actuator has positioned the headlamps below the nominal level, the headlamp level controller will disable the headlamp leveling actuator and maintain the lower than nominal level.

### 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

Important: When one of the suspension position sensor voltage reference or sensor signal circuits are shorted to ground, it may not possible to determine which suspension position sensor voltage reference or sensor signal circuits, front or rear, has failed. If this condition occurs, all suspension position sensor voltage reference and sensor signal circuits will have to be tested for a short to ground.

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 | Values | 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 B3420 02 present? | -- | Go to Step 6 | Go to Step 3
3 | Is DTC B3420 03 present? | -- | Go to Step 4 | Go to Step 5
4 | Test the rear suspension position sensor voltage reference and sensor signal circuits for an open, high resistance, or short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 9
5 | Test the rear suspension position sensor signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 9
6 |

1. Turn OFF the ignition.
2. Disconnect the rear suspension position sensor harness connector.
3. Turn ON the ignition, with the engine OFF.
4. Measure the voltage of the voltage reference circuit at the rear suspension position sensor harness connector.

Does the voltage measure less than the specified value?

4.49 V

Go to Step 7

Go to Step 8

7 | Locate and repair an open, high resistance, or short to ground in the rear suspension position sensor voltage reference circuit. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 10
8 | Test the rear suspension position sensor low reference circuit for an open, high resistance, or short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 9
9 | Inspect for poor connections at the harness connector of the rear suspension position sensor . Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11
10 | Inspect for poor connections at the harness connector of the headlamp level controller. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 13
11 | Important: After replacing the suspension position sensor, perform the headlamp level controller setup procedure. Refer to Headlamp Leveling Module Programming and Setup . Replace the rear suspension position sensor. Refer to Headlamp Leveling Switch Replacement .

Did you complete the replacement?

--

Go to Step 12

--

12 |

1. Turn ON the ignition, with the engine OFF.
2. Use the scan tool in order to clear the DTCs.
3. Operate the vehicle within the Conditions for Running the DTC.

Does the scan tool display B3420 as current?

--

Go to Step 13

Go to Step 14

13 | Important: After replacing the headlamp level controller, perform the setup procedure. Refer to Headlamp Leveling Module Programming and Setup . Replace the headlamp level controller. Refer to Control Module References . 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 text.

Does the DTC reset?

--

Go to Step 2

System OK