Pinpoint Test F: DTC U0120

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.

DTC Fault Trigger Conditions

DTC	Description	Fault Trigger Condition
PCM U0120:00	Lost Communication with Starter/ Generator Control Module: No Sub Type Information	Sets if the PCM does not detect communication through the LIN circuit. This can be a result of an open or short in the LIN circuit.

Possible Sources

Battery monitoring sensor
Generator
PCM
Wiring, terminals or connectors

Visual Inspection and Pre-checks

Inspect high current BJB for loose, damaged or corroded connections.
Inspect the BJB fuse 3 (275A).
Inspect the FEAD belt.
Inspect the battery monitoring sensor.

NOTE: Make sure battery voltage is greater than 12.2 volts prior to and during this pinpoint test.
NOTE: Do not have a battery charger attached during vehicle testing.

F1 COMPARE THE GENERATOR B+ CIRCUIT TO BATTERY VOLTAGE

Measure and record:

Positive Lead	Measurement / Action	Negative Lead
Courtesy of FORD MOTOR COMPANY	Courtesy of FORD MOTOR COMPANY	Courtesy of FORD MOTOR COMPANY

Measure:

Positive Lead	Measurement / Action	Negative Lead
C1011B-1	Courtesy of FORD MOTOR COMPANY	Ground

Is the voltage within 0.5 volt of the recorded battery voltage?

Yes

GO to F2

TIGHTEN or INSTALL a new generator B+ nut as needed. REFER to: Starter Generator - 3.5L V6 PowerBoost (CN) . VERIFY high current BJB fuse 3 (275A) is OK. If OK, REPAIR the circuit. If not OK, REFER to the OEM ELECTRICAL WIRING DIAGRAM INTRODUCTION to identify the possible causes of the circuit short.

F2 CHECK THE GENERATOR CAN (CONTROLLER AREA NETWORK) CIRCUIT FOR A SHORT TO VOLTAGE

Ignition OFF.

Disconnect Generator C1011A.

Disconnect PCM C175B.

Measure:

Positive Lead	Measurement / Action	Negative Lead
C1011A-2	Courtesy of FORD MOTOR COMPANY	Ground
C1011A-3	Courtesy of FORD MOTOR COMPANY	Ground

Is any voltage present?

Yes	REPAIR the circuit.

GO to F3

F3 CHECK THE GENERATOR CAN (CONTROLLER AREA NETWORK) CIRCUIT FOR A SHORT TO GROUND

Ignition OFF.

Measure:

Positive Lead	Measurement / Action	Negative Lead
C1011A-2	Courtesy of FORD MOTOR COMPANY	Ground
C1011A-3	Courtesy of FORD MOTOR COMPANY	Ground

Is the resistance greater than 10, 000 ohms?

Yes

GO to F4

No	REPAIR the circuit.

F4 CHECK THE GENERATOR CAN (CONTROLLER AREA NETWORK) CIRCUIT FOR AN OPEN

Measure:

Positive Lead	Measurement / Action	Negative Lead
C1011A-2	Courtesy of FORD MOTOR COMPANY	C175B-23
C1011A-3	Courtesy of FORD MOTOR COMPANY	C175B-8

Is the resistance less than 3 ohms?

Yes	INSTALL a new generator. REFER to: Starter Generator - 3.5L V6 PowerBoost (CN) . REPEAT the PCM self-test. If DTC U0120 is retrieved again, GO to F5

No	REPAIR the affected circuit.

F5 CHECK FOR CORRECT PCM (POWERTRAIN CONTROL MODULE) OPERATION

Ignition OFF.

Disconnect and inspect all PCM 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

Reconnect the PCM connectors. Make sure they seat and latch correctly.

Operate the system and determine if the concern is still present.

Is the concern still present?

Yes

CHECK OASIS for any applicable Technical Service Bulletins (TSBs). If a TSB exists for this concern, DISCONTINUE this test and FOLLOW the TSB instructions. If no Technical Service Bulletins (TSBs) address this concern, Refer to PCM GUIDED ROUTINE TESTING
Internet Explorer version 11 or greater is required to perform this Pinpoint Test.

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.