For circuit and connector information, refer to Wiring Diagrams Cell 46.
Normal Operation and Fault Symptoms
The RCM provides yaw rate, roll rate, lateral and longitudinal accelerometer data to the Stability/Traction Control system over a dedicated CAN bus. If the RCM detects a communication fault with the ABS module or the dedicated CAN bus circuits, it sets DTC U0028:08 or U0028:88.
The RCM does not request the IPC to illuminate the airbag warning indicator if DTC U0028:08 or U0028:88 is set.
DTC Fault Trigger Conditions
Trouble Code
Description
Fault Trigger Conditions
U0028:08
Vehicle Communication Bus A: Bus Signal/Message Failures
The fault is indicated when the RCM does not receive messages from the ABS module on the dedicated CAN bus for 5 seconds. An open dedicated CAN circuit, an incorrectly installed ABS module, or a loss of power and/or ground to the ABS module can set this DTC.
U0028:88
Vehicle Communication Bus A: Bus Off
The fault is indicated when the RCM detects the dedicated CAN circuits shorted to ground, shorted to voltage, or shorted to each other.
Possible Causes
Wiring, Terminals or Connectors
ABS Module
RCM
Visual Inspection and Preliminary Diagnosis
Inspect the wiring harness for damage.
Inspect the ABS module connector for loose or damaged connectors.
PINPOINT TEST A: U0028:08 AND U0028:88
NOTE: Most concerns are related to connector and/or wiring issues. Perform a thorough inspection and check before proceeding to the Pinpoint Test.
NOTE: Only disconnect or reconnect SRS components when instructed to do so in the Pinpoint Test step. Failure to follow this instruction may result in an incorrect SRS diagnosis.
NOTE: Always verify the correct SRS component is installed. Parts released for other vehicles may be incompatible even if they appear physically similar. Check the part number listed in the Ford parts catalog to confirm the correct component is installed. If an incorrect SRS component is installed, diagnostic trouble codes (DTCs) may be set.
NOTE: Before returning the vehicle to the customer, the SRS must be fully functional and operating correctly.
A1 REMOVE RCM (RESTRAINTS CONTROL MODULE) DIAGNOSTIC TROUBLE CODES (DTCS)
WARNING: Before starting any service procedure in this section, refer to the Safety Warnings in Section 100-00 General Information. Failure to follow this instruction may result in serious personal injury. REFER TO: Pyrotechnic Device Handling Precautions (100-00 General Information, Description and Operation).
The ignition is on.
Using the diagnostic scanner, perform the RCM self-test.
Was DTC U0028:08 or U0028:88 retrieved on demand during the self-test?
Yes
This fault cannot be cleared until it is repaired and the DTC is no longer retrieved on demand during the self-test. For DTC U0028:08 GO to A2 For DTC U0028:88 GO to A5
No
This is an intermittent fault when present as a Continuous Memory Diagnostic Trouble Code (CMDTC) only. GO to A13
A2 CHECK THE RCM (RESTRAINT CONTROL MODULE) PART NUMBER
Using the diagnostic scanner data log function, retrieve and record the RCM part number.
Compare the recorded part number with the number listed in the parts catalog and verify the correct RCM is installed in the vehicle.
Is the correct RCM installed?
Yes
GO to A3
No
INSTALL the correct RCM. REFER to: Restraints Control Module (RCM) (501-20B Supplemental Restraint System, Removal and Installation). GO to A14
A3 CHECK THE ABS (ANTI-LOCK BRAKE SYSTEM) MODULE PART NUMBER
Using the scan tool log function, retrieve and record the ABS module part number.
Compare the recorded part number with the number listed in the parts catalog and make sure the correct ABS module is installed in the vehicle.
Is the correct ABS module installed?
Yes
GO to A4
No
INSTALL the correct ABS module. REFER to: Hydraulic Control Unit (HCU) (206-09 Anti-Lock Brake System (ABS) and Stability Control System, Removal and Installation). GO to A14
A4 CHECK THE HS-CAN (HIGH-SPEED CONTROLLER AREA NETWORK) COMMUNICATION (ABS (ANTI-LOCK BRAKE SYSTEM) MODULE COMMUNICATION)
NOTE: The network test does not check the dedicated CAN communication between the ABS module and the RCM. Using the diagnostic scan tool, perform the network test.
Did the network test pass (ABS module communicates with the scan tool)?
Yes
GO to A5
No
CHECK the HS-CAN/ABS module communication fault. REFER to: Communication Network (Module Communications Network 418-00). GO to A14
A5 CHECK THE DEDICATED CAN (CONTROLLER AREA NETWORK) CIRCUITS FOR AN OPEN
Ignition OFF.
De-power the SRS. REFER to: Supplemental Restraint System (SRS) Disabling and Re-enabling (501-20B Supplemental Restraint System, General Procedures).
Disconnect: RCM C310A and C310B.
Disconnect: ABS Module C135.
Action: Click to display the connectors
Positive lead
Measurement/Action
Negative lead
C310B-60
C135-32
C310B-59
C135-33
Is the resistance less than 5 ohms?
Yes
For DTC U0028:08 GO to A9 For DTC U0028:88 GO to A6
No
REPAIR the faulty circuit. For wiring diagrams and connector information, refer to Wiring Diagrams Cell 5. GO to A14
A6 CHECK THE DEDICATED CAN (CONTROLLER AREA NETWORK) CIRCUITS FOR A SHORT TO VOLTAGE
Reset the SRS. Do not check the SRS at this time. REFER TO: Supplemental Restraint System (SRS) Disarming and Rearming (501-20B Supplemental Restraint System, General Procedures).
The ignition is on.
Action: Click to display the connectors
Positive lead
Measurement/Action
Negative lead
C135-32
Ground
C135-33
Ground
Is there voltage present on either circuit?
Yes
REPAIR the faulty circuit(s). For wiring diagrams and connector information, refer to Wiring Diagrams Cell 5. GO to A14
No
GO to A7
A7 CHECK THE DEDICATED CAN (CONTROLLER AREA NETWORK) CIRCUITS FOR A SHORT TO GROUND
Ignition OFF.
De-power the SRS. REFER to: Supplemental Restraint System (SRS) Disabling and Re-enabling (501-20B Supplemental Restraint System, General Procedures).
Action: Click to display the connectors
Positive lead
Measurement/Action
Negative lead
C135-32
Ground
C135-33
Ground
Is the resistance greater than 10000 ohms?
Yes
GO to A8
No
REPAIR the faulty circuit(s). For wiring diagrams and connector information, refer to Wiring Diagrams Cell 5. GO to A14
A8 CHECK THE DEDICATED CAN (CONTROLLER AREA NETWORK) CIRCUITS FOR A SHORT CIRCUIT TO EACH OTHER
Action: Click to display the connectors
Positive lead
Measurement/Action
Negative lead
C135-32
C135-33
Is the resistance greater than 10000 Ohms?
Yes
GO to A9
No
REPAIR the circuit(s). For wiring diagrams and connector information, refer to Wiring Diagrams Cell 5. GO to A14
A9 CHECK THE RCM (RESTRAINT CONTROL MODULE) TERMINATING RESISTOR
Connect: RCM C310B.
Action: Click to display the connectors
Positive lead
Measurement/Action
Negative lead
C135-32
C135-33
Is the resistance between 108 and 132 ohms?
Yes
GO to A10
No
GO to A11
A10 CHECK THE ABS (ANTI-LOCK BRAKE SYSTEM) MODULE TERMINATING RESISTOR
Disconnect: RCM C310B.
Connect: ABS Module C135.
Action: Click to display the connectors
Positive lead
Measurement/Action
Negative lead
C310B-59
C310B-60
Is the resistance between 108 and 132 ohms?
Yes
For DTC U0028:08 GO to A11 For DTC U0028:88 GO to A12
No
GO to A12
A11 CONFIRM THE RCM (RESTRAINT CONTROL MODULE) FAULT
Before reconnecting any previously disconnected SRS component:
inspect the connector(s) (including any integral connectors) for pushed-out, loose or spread terminals, and loose or chafed wire connections at the terminals.
inspect the wiring harness for damage, pinching, or cut or pierced wires.
check the RCM C310A and C310B connector position assurance (CPA) lever/latch for proper operation.
Inspect the ABS module C135 for dirt, corrosion, water intrusion, pushed-out, loose or spread terminals, and loose or worn connection wire on the terminals.
repair any problems found. Refer to Wiring Diagrams Cell 5 for schematic and connector information.
Connect: ABS Module C135.
Connect: RCM C310A and C310B.
Reset the SRS. Do not check the SRS at this time. REFER TO: Supplemental Restraint System (SRS) Disarming and Rearming (501-20B Supplemental Restraint System, General Procedures).
The ignition is on.
Using the diagnostic scanner, perform the RCM self-test.
Was the original DTC retrieved on demand during the self-test?
Yes
CHECK OASIS for any applicable Technical Service Bulletins (TSBs). If a TSB exists for this concern, STOP this test and FOLLOW the TSB instructions. If no TSB applies to this concern, INSTALL a new RCM. REFER to: Restraints Control Module (RCM) (501-20B Supplemental Restraint System, Removal and Installation). GO to A14
No
During the diagnosis, the condition became intermittent. Do not install new SRS components at this time. Install SRS components only if directed by the pinpoint test. GO to A13
A12 CONFIRM THE ABS (ANTI-LOCK BRAKE SYSTEM) MODULE FAULT
Before reconnecting any previously disconnected SRS component:
inspect the connector(s) (including any integral connectors) for pushed-out, loose or spread terminals, and loose or chafed wire connections at the terminals.
inspect the wiring harness for damage, pinching, or cut or pierced wires.
check the RCM C310A and C310B connector position assurance (CPA) lever/latch for proper operation.
Inspect the ABS module C135 for dirt, corrosion, water intrusion, pushed-out, loose or spread terminals, and loose or worn connection wire on the terminals.
repair any problems found. Refer to Wiring Diagrams Cell 5 for schematic and connector information.
Connect: ABS Module C135.
Connect: RCM C310A and C310B.
Reset the SRS. Do not check the SRS at this time. REFER TO: Supplemental Restraint System (SRS) Disarming and Rearming (501-20B Supplemental Restraint System, General Procedures).
The ignition is on.
Using the diagnostic scanner, perform the RCM self-test.
Was the original DTC retrieved on demand during the self-test?
Yes
CHECK OASIS for any applicable Technical Service Bulletins (TSBs). If a TSB exists for this concern, STOP this test and FOLLOW the TSB instructions. If no TSB applies to this concern, INSTALL a new ABS module. REFER to: Hydraulic Control Unit (HCU) (206-09 Anti-Lock Brake System (ABS) and Stability Control System, Removal and Installation). GO to A14
No
During the diagnosis, the condition became intermittent. Do not install new SRS components at this time. Install SRS components only if directed by the pinpoint test. GO to A13
A13 CHECK FOR INTERMITTENT FAULT
Ignition OFF.
De-power the SRS. REFER to: Supplemental Restraint System (SRS) Disabling and Re-enabling (501-20B Supplemental Restraint System, General Procedures).
Disconnect: ABS Module C135.
Disconnect: RCM C310A and C310B.
inspect the connector(s) (including any integral connectors) for pushed-out, loose or spread terminals, and loose or chafed wire connections at the terminals.
inspect the wiring harness for damage, pinching, or cut or pierced wires.
check the RCM C310A and C310B connector position assurance (CPA) lever/latch for proper operation.
Inspect the ABS module C135 for dirt, corrosion, water intrusion, pushed-out, loose or spread terminals, and loose or worn connection wire on the terminals.
repair any problems found. Refer to Wiring Diagrams Cell 5 for schematic and connector information.
Connect: ABS Module C135.
Connect: RCM C310A and C310B.
Reset the SRS. Do not check the SRS at this time. REFER TO: Supplemental Restraint System (SRS) Disarming and Rearming (501-20B Supplemental Restraint System, General Procedures).
The ignition is on.
Using the diagnostic scanner, perform the RCM self-test.
Was DTC U0028:08 or U0028:88 retrieved on demand during the self-test?
Yes
This fault cannot be cleared until it is repaired and the DTC is no longer retrieved on demand during the self-test. CHECK for possible causes of the intermittent fault in previously worked areas, especially the terminals and pins of any electrical connector that was disconnected. REPAIR any faulty wiring, terminal or connector found. For wiring diagrams and connector information, refer to Wiring Diagrams Cell 5. GO to A14
No
The fault is not present and cannot be recreated at this time. Do not install any new SRS components at this time. Install SRS components only when directed by the pinpoint test. GO to A14.
A14 CHECK THE SUPPLEMENTAL RESTRAINT SYSTEM (SRS) DIAGNOSTIC TROUBLE CODES (DTCS)
Connect: RCM C310A and C310B (if previously disconnected).
If previously instructed to disable the SRS, re-enable the SRS. Do not check the SRS at this time. Refer to: Supplemental Restraint System (SRS) Disabling and Arming (501-20B Supplemental Restraint System, General Procedures).
The ignition is on.
Using the diagnostic scanner, perform the RCM self-test.
Using the diagnostic scan tool, perform a self-test of the ABS module.
Are any RCM and/or ABS module diagnostic trouble codes (DTCs) retrieved on demand during the self-test?
Yes
Do not clear any diagnostic trouble codes (DTCs) until all diagnostic trouble codes (DTCs) have been resolved. For RCM diagnostic trouble codes (DTCs): REFER TO: Supplemental Restraint System (SRS) (501-20 Supplemental Restraint System). For ABS module diagnostic trouble codes (DTCs): REFER TO: Anti-Lock Brake System (ABS) and Stability Control System (206-09 Anti-Lock Brake System (ABS) and Stability Control System, Diagnosis and Testing).
No
CLEAR the Continuous Memory Diagnostic Trouble Codes (CMDTCs) in all modules. VERIFY the SRS. Repair is complete. RETURN the vehicle to the customer.
?
Test yourself
A quick Ford Fiesta quiz: every answer comes with an explanation and a link to the manual page.
WARNING: Before starting any service procedure in this section, refer to the Safety Warnings in Section 100-00 General Information. Failure to follow this instruction may result in serious personal injury. 
