Ford Mustang Hill Start Assist Not Available

In today daily article,I want to share a real repair case about how to repair Ford Mustang hill start assist not available problem.Hope this will bring you some enlightenment on your work.More topics about Hill Start Assist,please refer to:Hill Start Assist


Vhicle info:

Ford Mustang 2.3T

Mileage:2,000 miles


Trouble syptoms:

ESP light on

Airbag light on occasionally

Screen show “Hill start assist not available”

Trobuel Diagnosis:

Technicians drove the car to identify the trobule owner discribed,and found it as below:

1.Engine started smoothly

2.There was not any warning light on the instrument cluster.

3.Tried to start the engine several time,the screen show “Hill start assist not available”.

4.After off the engine,there were noise sound “da da da”,the owner believed it was root in throttle.

5.Clearance lights located in left and right headlight assembly flashed occasionally after engine power off.


Connect the diagnostic tool (Ford IDS) to the car,read the below DTCs.

U0100:Lost Communication with ECM/PCM “A” code.The generic OBD trouble code U0100 is a serious situation where the signals between the electronic control module (ECM) or the powertrain control module (PCM) and a particular module have been lost. There could also be a problem with the CAN bus wiring disrupting communications.

U0151:Lost Communication with Restraints Control (RCM) Module.This code means that the Restraints Control (RCM) Module and other control modules on the vehicle are not communicating with each other. The circuit most often used to communicate with is known as Controller Area Network bus communications, or simply put, CAN bus.

U0415:Invalid Data Received From ABS Control Module.The U0415 code sets when the TCM fails to receive the Anti-Lock Brake System (ABS) Control Module message within the defined amount of time.

B0061:Passenger Seatbelt Tension Sensor (Subfault).This trobule code don’t have further diagnostic information.

U0452:Invalid Data Received From Restraints Control Module.


The trouble codes listed above,4 of them is releated to the communication trobule,and the guide direction of the DTCs is difficult to determin trouble reason,so techicians decided to find the cause by syptoms.


Firstly,the technicians want to find the cause of clearance lights flashing.Check the relevant circuit diagram(show as below),disconnected the connector C1021,and detected the voltage of terminal 3 of C1021 connector by multimeter,it displayed 4.75V(normal 0V).Detected the voltage of fuse F37,F21,F34,F19,F22 orderly,all of them showed 4.75V.Only voltage of fuse F34 was normal(12.11V).

It most likely the PCM,sub-module of BCM or relevant wire harness caused this problem.

View the car repair log,the vehicle had not repaired by accident.It is easy to replace the BCM,so technician replaced and programed the BCM firstly.But the trobule still existed,so technicians belived that the sub-module at fault.And determined to locate the cause by disconnecting the power of sub-module one by one.Pulled out the fuse F21,F35,F19,F22 one by one,the voltage of C1021 terminal 3 changed from 4.75V to 0V when pulling the fuse F22 out,so technicians suspect the occupant classification system module(OCSM) or relevant wire harness at fault.


Located the occupant classification system module(OCSM),and found there was a electrical accessory was installed on it(show below).This electronic accessory power by the passenger identification module,its GND on the fuse F22.After power off,the electrical accessory worked as a voltage divider,so the voltage shows 4.75V,and the headlight assembly,power control module,ABS module,electrical steering column control module supply power even after turn off the ignition,then it caused below trobule syptom.


Remove teh electrical accessories,clear the trobule code,tested the car again and again,the trobuel syptoms disappeared.

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