Auxiliary Step / Running Board: Testing and Inspection
Power Assist Step Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (with HP2) (Initial Inspection and Diagnostic Overview)Diagnostic System Check - Vehicle (without HP2) (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
The assist step control module (ASC) controls the assist step actuators to extend or retract the assist steps. 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 ASC 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 ASC module supplies the actuator motor with a 12-volt control circuit and a ground control circuit. The ASC module controls the direction of the actuator by changing the polarity of the control circuits.
Reference Information
Schematic Reference
Step/Running Board Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Running Board Description (Description and Operation)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Verification
1. Observe the scan tool ASC Disable Switch parameter while activating and deactivating the power assist steps. The reading should change between Active and Inactive.
• If the parameter does not change between the specified values, refer to ASC Disable Switch Circuit Test
2. Power assist steps enabled, OPEN and CLOSE each vehicle door, the assist steps should extend when the door is OPENED, and retract when the door is CLOSED.
• If the function does not perform as specified, refer to ASC Actuator Circuit Test.
Circuit/System Testing
ASC Disable Switch Circuit Test
1. Ignition OFF, disconnect the harness connector at the IP multifunction switch.
2. Test for less than 10 ohms between the listed ground circuit terminal and ground.
* X88/Z88 Terminal 3
* Z75 terminal 1
• If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition ON, verify the scan tool ASC Disable Switch parameter is Inactive.
• If not the specified value, test the signal circuit terminal 9 for a short to ground. If the circuit tests normal, replace the ASC module.
4. Install a 3A fused jumper wire between the signal circuit terminal 9 and ground. Verify the scan tool ASC Disable Switch parameter is Active.
• If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ASC module.
5. If all circuits test normal, test or replace the IP multifunction switch.
ASC Actuator Circuit Test
1. Ignition OFF, disconnect the harness connector at the appropriate actuator.
2. Scan tool disconnected, test for less than 20 ohms between the low reference circuit terminal C and ground.
• If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ASC module.
3. Ignition ON, command the appropriate actuator with a scan tool while using the DMM Min/Max function to capture voltage. Test for greater than 9 volts between the 10-volt reference circuit terminal D and ground.
• If less than the specified range, test the 10-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ASC module.
4. Command the appropriate actuator with a scan tool while using the DMM Min/Max function to capture voltage. Test for greater than 9 volts between the signal circuit terminal E and ground.
• If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ASC module.
5. Using a scan tool, command the appropriate actuator both directions while using the DMM Min/Max function to capture voltage. Test for greater than 2 volts between the control circuit terminal A and ground.
• If less than the specified range, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ASC module.
6. Using a scan tool, command the appropriate actuator both directions while using the DMM Min/Max function to capture voltage. Test for greater than 2 volts between the control circuit terminal B and ground.
• If less than the specified range, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ASC module.
7. If all circuits test normal, replace the ASC actuator.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Assist Step Motor Replacement (Power BRS) (Service and Repair)
* Control Module References (Programming and Relearning) for ASC module replacement, setup, and programming