B051C

DTC B051A, B051B, B051C, or B051D


Diagnostic Instructions

-Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

-Review Strategy Based Diagnosis for an overview of the diagnostic approach.

- Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC B051A 0B:Left Side Assist Step Motor Control Circuit Current Above Threshold

DTC B051A 01:Left Side Assist Step Motor Control Circuit Short to Battery

DTC B051A 02:Left Side Assist Step Motor Control Circuit Short to Ground

DTC B051A 04:Left Side Assist Step Motor Control Circuit Open Circuit

DTC B051B 0B:Right Side Assist Step Motor Control Circuit Current Above Threshold

DTC B051B 01:Right Side Assist Step Motor Control Circuit Short to Battery

DTC B051B 02:Right Side Assist Step Motor Control Circuit Short to Ground

DTC B051B 04:Right Side Assist Step Motor Control Circuit Open Circuit

DTC B051C 01:10 V Reference Circuit Short to Battery

DTC B051C 02:10 V Reference Circuit Short to Ground

DTC B051C 2A:Left Side Assist Step Position Sensor Circuit Too Many Pulses

DTC B051C 22:Left Side Assist Step Position Sensor Circuit Low Time < Minimum

DTC B051C 29:Left Side Assist Step Position Sensor Circuit Too Few Pulses

DTC B051C 62:Left Side Assist Step Position Sensor Circuit Actuator Stuck Open

DTC B051C 63:Left Side Assist Step Position Sensor Circuit Actuator Stuck Closed

DTC B051D 2A:Right Side Assist Step Position Sensor Circuit Too Many Pulses

DTC B051D 22:Right Side Assist Step Position Sensor Circuit Low Time < Minimum

DTC B051D 29:Right Side Assist Step Position Sensor Circuit Too Few Pulses

DTC B051D 62:Right Side Assist Step Position Sensor Circuit Actuator Stuck Open

DTC B051D 63:Right Side Assist Step Position Sensor Circuit Actuator Stuck Closed

Diagnostic Fault Information










Circuit/System Description

The Assist Step Control Module controls the running board actuators to extend or retract the running boards. Each actuator consists of an electric motor and a potentiometer. The module supplies a low reference and 10-volt reference source voltage to the potentiometer. The Assist Step Control Module monitors the voltage drop across the potentiometer on the position signal circuit. When the actuator shaft rotates, the voltage on the position signal circuit changes. The Assist Step Control Module supplies the actuator motor with a 12-volt control circuit and a ground control circuit. The assist step module controls the direction of the actuator by changing the polarity of the control circuits.

Conditions for Running the DTC

-The ignition is ON.

-Ignition voltage is between 9-16 volts.

-The assist step disable switch is not pressed.

Conditions for Setting the DTC


B051A 0B, B051B 0B


The motor control circuits are shorted together.


B051A 01, B051B 01


A motor control circuit is shorted to battery voltage.


B051A 02, B051B 02


A motor control circuit is shorted to ground.


B051A 04, B051B 04


A motor control circuit is open.


B051C 01


The hall sensor 10 V reference is shorted to battery voltage.


B051C 02


The hall sensor 10 V reference is shorted to ground.


B051C 2A, B051D 2A


The hall sensor counts are greater than what is required to extend or stow the running board.


B051C 22, B051D 22


The hall sensor signal is noisy.


B051C 29, B051D 29


No hall sensor counts are detected while the motor is active.


B051C 62, B051D 62


The running board stow time is greater than 4 seconds.


B051C 63, B051D 63


The running board extend time is greater than 4 seconds.

Action Taken When the DTC Sets

Driver A and driver B circuits are deactivated for the appropriate actuator.

Conditions for Clearing the DTC

-The DTC becomes history when the Assist Step Control Module no longer detects the condition that set the DTC.

-The history DTC will clear after 50 fault free ignition cycles.

Reference Information

Schematic Reference

Step/Running Board Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Running Board Description

Electrical Information Reference

- Circuit Testing

- Connector Repairs

- Testing for Intermittent Conditions and Poor Connections

- Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1.Verify the left and right side running boards extend and retract when opening and closing the left and right side doors.

If the both running boards do not extend or retract

Perform Circuit/System Testing

⇓
If the running boards extend and retract
2.All OK.

Circuit/System Testing

Note:If DTC B051C and/or B051D with symptom bytes 62, 63, or 2A is set, verify that the assist step motor wedge is present and the assist step motor wedge bolt is tight prior to proceeding with the following diagnostic steps. Refer to Assist Step Motor Replacement for part location and tightening specifications.

1.Ignition OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down. Disconnect the harness connector at the appropriate actuator.

2.Test for less than 10 Ω between the low reference circuit terminal C and ground.
-
If 20 Ω or greater

2.1Ignition OFF, disconnect the harness connector at the Assist Step Control Module.

2.2Test for less than 2 Ω in the low reference circuit end to end.

-If 2 Ω or greater, repair the open/high resistance in the circuit.

-If less than 2 Ω, replace the Assist Step Control Module.
⇓
If less than 20 Ω
3.Disconnect both Running Board actuators. Ignition ON.

4.Test for 9 - 11 V between the Running Board - Left 10 V reference circuit terminal D and ground while commanding the actuator with the scan tool.
-
If less than 9 V

4.1Ignition OFF, disconnect the X2 harness connector at the Assist Step Control Module.

4.2Test for infinite resistance between the following 10 V reference circuit terminals and ground.

-X2 Terminal A Running Board - Left

-X2 Terminal B Running Board - Right

-If less than infinite resistance, repair the short to ground on the appropriate circuit.

⇓If infinite resistance

4.3Test for less than 2 Ω in the 10 V reference circuits end to end.

-If 2 Ω or greater, repair the open/high resistance in the circuit.

-If less than 2 Ω replace the Assist Step Control Module.
-
If greater than 11 V

4.1Ignition OFF, disconnect the X2 harness connector at the Assist Step Control Module control module, ignition ON.

4.2Test for less than 1 V between the following 10 V reference circuit and ground.

-X2 Terminal A Running Board - Left

-X2 Terminal B Running Board - Right

-If 1 V or greater, repair the short to voltage on the appropriate circuit.

-If less than 1 V, replace the Assist Step Control Module.
⇓
If between 9-11 V
5.Ignition OFF. Connect Running Board - Left actuator. Ignition ON.

6.Test for 9 - 11 V between the 10 V reference circuit terminal D at the right side and ground while commanding the actuator with the scan tool.
-
If not between 9-11 V

Test or replace Running Board - Left actuator.

⇓
If between 9-11 V
7.Ignition OFF. Disconnect Running Board - Left, connect Running Board - Right. Ignition ON.

8.Test for 9 - 11 V between the 10 V reference circuit terminal D at the left side and ground while commanding the actuator with the scan tool.
-
If not between 9-11 V

Test or replace Running Board - Right actuator.

⇓
If between 9-11 V
9.Test for greater than 9 V between the appropriate signal circuit terminal E and ground while commanding the actuator with the scan tool.
-
If not greater than 9 V

9.1Ignition OFF, disconnect the X2 harness connector at the Assist Step Control Module.

9.2Test for infinite resistance between the following signal circuit terminals and ground.

-X2 Terminal C Running Board - Left

-X2 Terminal D Running Board - Right

-If less than infinite resistance, repair the short to ground on the appropriate circuit.

⇓If infinite resistance

9.3Test for less than 2 Ω in the signal circuits end to end.

-If 2 Ω or greater, repair the open/high resistance in the circuit.

-If less than 2 Ω replace the Assist Step Control Module.
-
If 9 V or greater

10.Connect a test lamp between the control circuit terminal A and the control circuit terminal B.

11.Verify the test lamp turns on and off while commanding the appropriate board to Extend and Retract with a scan tool.
-
If the test lamp is always OFF

11.1Ignition OFF, disconnect the harness connector at the Assist Step Control Module.

11.2Test for less than 1 V between the control circuit and ground.

-If 1 V or greater, repair the short to voltage on the circuit.

⇓If less than 1 V

11.3Ignition OFF.

11.4Test for less than 2 Ω in the control circuit end to end.

-If 2 Ω or greater, repair the open/high resistance in the circuit.

-If less than 2 Ω, replace the Assist Step Control Module.
-
If the test lamp is always ON

11.1Ignition OFF, disconnect the harness connector at the Assist Step Control Module.

11.2Test for infinite resistance between the control circuit and ground.

-If less than infinite resistance, repair the short to ground on the circuit.

-If infinite resistance, replace the Assist Step Control Module.
⇓
If the test lamp turns ON and OFF
12.Test or replace the appropriate assist step motor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

- Assist Step Motor Replacement

- Control Module References for Assist Step Control Module replacement, programming and setup.