Pinpoint Test An: Powertrain Can (Controller Area Network) Bus Off

WARNING: This page is about a different car, the 2021 Ford F-150. However, it is still accessible from the selected car via links, so may be relevant.

Refer to Wiring Diagrams ELECTRONIC ENGINE CONTROLS - 3.0L DIESEL for schematic and connector information.

Normal Operation and Fault Conditions

In addition to communicating over FD-CAN, the TCM also communicates with the PCM and GSM over a private Powertrain CAN. The TCM will set a DTC when it has not received any messages from other modules on the network for 10 seconds. If the network is down, other modules on the network may set a DTC as well.

DTC Fault Trigger Conditions

DTC	Description	Fault Trigger Condition
TCM U0037:00	Vehicle Communication Bus B: No Sub Type Information	This DTC illuminates the wrench light in conjunction with U0074.
TCM U0074:00	Control Module Communication Bus "B" Off: No Sub Type Information	This DTC indicates the TCM did not receive any messages from other modules on the Powertrain CAN for 10 seconds or longer.

Possible Sources

Connectors damaged or pushed-out terminals, corrosion, loose wires and missing or damaged seals
Circuit open or shorted
Another module taking down the CAN bus
TCM fault

AN1 CHECK FOR POWERTRAIN CAN (CONTROLLER AREA NETWORK) BUS DIAGNOSTIC TROUBLE CODES (DTCS) IN OTHER MODULES
- Using a diagnostic scan tool, retrieve all continuous memory diagnostic trouble codes (CMDTCs) from all modules.
Is a powertrain CAN bus DTC present in other modules on the network?

Yes GO to AN2

No GO to AN5

AN2 CHECK THE POWERTRAIN CAN (CONTROLLER AREA NETWORK) CIRCUITS FOR A SHORT TO GROUND

Ignition OFF.

Disconnect TCM C1822.

Inspect the connector for damaged or pushed out terminals, corrosion, loose wires and missing or damaged seals.

Measure:

Positive Lead	Measurement / Action	Negative Lead
C1822-45	Courtesy of FORD MOTOR COMPANY	Ground
C1822-46	Courtesy of FORD MOTOR COMPANY	Ground

Are the resistances greater than 1, 000 ohms?

Yes

GO to AN5

GO to AN3

AN3 CHECK EACH MODULE ON THE POWERTRAIN CAN (CONTROLLER AREA NETWORK) FOR A SHORT TO GROUND

Refer to Wiring Diagrams ELECTRONIC ENGINE CONTROLS - 3.0L DIESEL for powertrain CAN module and connector information.

Disconnect modules that communicate on Powertrain CAN one at a time.

Each time a module is disconnected, measure:

Positive Lead	Measurement / Action	Negative Lead
C1822-45	Courtesy of FORD MOTOR COMPANY	Ground
C1822-46	Courtesy of FORD MOTOR COMPANY	Ground

Did the resistance increase to greater than 1, 000 ohms when one of the modules was disconnected?

Yes	To check the operation of that module, GO to AN4

No	REFER to the OEM ELECTRICAL WIRING DIAGRAM INTRODUCTION to identify and repair the short to ground in the powertrain CAN circuit.

AN4 CHECK THE SUSPECT MODULE FOR CORRECT OPERATION

Ignition OFF.

Disconnect and inspect all suspect module connectors.

Repair:
- corrosion (install new connector or terminals - clean module pins)
- damaged or bent pins - install new terminals/pins
- pushed-out pins - install new pins as necessary

Connect the suspect module connectors. Make sure they seat and latch correctly.

Operate the system and verify the concern is still present.

Is the concern still present?

Yes

CHECK for an applicable TSB, GSB, SSM, or FSA. If a service bulletin exists for this concern, discontinue this test and follow bulletin instructions. If none address this concern, INSTALL a new suspect module. For a PCM concern, Refer to PCM GUIDED ROUTINE TESTING
Internet Explorer version 11 or greater is required to perform this Pinpoint Test. For a GSM concern, INSTALL a new GSM. REFER to: (303-14F Electronic Engine Controls - 3.0L Power Stroke Diesel, Removal and Installation).

No	The system is operating correctly at this time. The concern may have been caused by module connections. ADDRESS the root cause of any connector or pin issues.

AN5 CHECK THE POWERTRAIN CAN (CONTROLLER AREA NETWORK) CIRCUITS FOR AN OPEN

Ignition OFF.

Disconnect TCM C1822 (if not previously disconnected).

Disconnect PCM C1233B.

Disconnect GSM C3245 (for vehicles equipped with console shift).

Disconnect GSM C2503 (for vehicles equipped with column shift).

Inspect the connectors for damaged or pushed out terminals, corrosion, loose wires and missing or damaged seals.

For vehicles equipped with console shift, measure:

Positive Lead	Measurement / Action	Negative Lead
C1822-45	Courtesy of FORD MOTOR COMPANY	C3245-13
C1822-46	Courtesy of FORD MOTOR COMPANY	C3245-14

For vehicles equipped with column shift, measure:

Positive Lead	Measurement / Action	Negative Lead
C1822-45	Courtesy of FORD MOTOR COMPANY	C2503-14
C1822-46	Courtesy of FORD MOTOR COMPANY	C2503-13

For all vehicles, measure:

Positive Lead	Measurement / Action	Negative Lead
C1822-45	Courtesy of FORD MOTOR COMPANY	C1233B-15
C1822-46	Courtesy of FORD MOTOR COMPANY	C1233B-14

Are the resistances less than 3 ohms?

Yes

GO to AN6

No	REPAIR the open circuit.

AN6 INSPECT THE POWERTRAIN CAN (CONTROLLER AREA NETWORK) CONNECTORS
- Ignition OFF.
- Refer to Wiring Diagrams ELECTRONIC ENGINE CONTROLS - 3.0L DIESEL for schematic and connector information. Disconnect all in-line CAN connectors between the TCM, PCM and GSM.
- Using a good light source, inspect all disconnected electrical connectors for the following:
  - corrosion (install new connector or terminals - clean module pins)
  - damaged or bent pins - install new terminals/pins
  - pushed-out pins - install new pins as necessary
  - spread terminals - install new terminals as necessary
Are any connector or pin issues present?

Yes REPAIR any connector or pin issues.

No GO to AN7

AN7 ATTEMPT TO DUPLICATE THE CONCERN

Ignition OFF.

Reconnect all disconnected electrical connectors. Make sure they seat and latch correctly.

Using a diagnostic scan tool, clear all diagnostic trouble codes (DTCs) from the TCM.

Road test the vehicle.

Using a diagnostic scan tool, carry out the TCM self-test.

Is DTC U0037 and/or U0074 present?

Yes

GO to AN8

No	The fault is not present at this time. It might have been caused by a loose or corroded connector, or an intermittent fault condition. ADDRESS the root cause of any connector or pin issues.

AN8 CHECK FOR CORRECT TCM (TRANSMISSION CONTROL MODULE) OPERATION

Ignition OFF.

Disconnect and inspect the TCM connector.

Repair:
- corrosion (install new connector or terminals - clean module pins)
- damaged or bent pins - install new terminals/pins
- pushed-out pins - install new pins as necessary

Connect the TCM connector. Make sure it seats and latches correctly.

Operate the system and verify the concern is still present.

Is the concern still present?

Yes

CHECK for an applicable TSB, GSB, SSM, or FSA. If a service bulletin exists for this concern, discontinue this test and follow bulletin instructions. If none address this concern, INSTALL a new TCM. REFER to: Transmission Control Module (TCM) . CARRY OUT the transmission strategy download. REFER to: Transmission Strategy Download .

No	The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. ADDRESS the root cause of any connector or pin issues.