Pinpoint Test B: The Trailer Brakes Are Always Engaged

Refer to TRAILER/CAMPER ADAPTER for schematic and connector information.
Normal Operation and Fault Conditions

The braking energy provided to the trailer is modulated with a PWM signal that varies between 0 volts and battery voltage, according to the TBM gain setting, the higher the duty cycle the more braking power available. With the vehicle stationary and with the manual slider switch fully to the left with a gain of 10, there should be 10-12 volts supplied to pin 3 of the 7-pin trailer tow connector C4099. The TBM also receives information from the stoplamp switch from the PCM over the HS-CAN.

Possible Sources
- Wiring, terminals or connectors
- TBM
- Trailer
Visual Inspection and Pre-checks
- Make sure AJB fuses 71 (30A) and 50 (10A) are OK.
- Make sure the trailer brakes are electric-magnet actuated drum type brakes.
NOTE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may cause damage to the connector.

B1 VERIFY VEHICLE STOPLAMP OPERATION
- Ignition ON.
- Monitor the vehicle stoplamps while pressing and releasing the brake pedal.
Do the vehicle stoplamps operate correctly?

Yes GO to B4

No GO to B2

B2 CHECK FOR PCM (POWERTRAIN CONTROL MODULE) DIAGNOSTIC TROUBLE CODES (DTCS)
- Using a diagnostic scan tool, carry out the PCM KOEO self-test.
Are there any Diagnostic Trouble Codes (DTCs) present in the PCM?

Yes DIAGNOSE all PCM Diagnostic Trouble Codes (DTCs). REFER to: appropriate Electronic Engine Control article .

No GO to B3

B3 CHECK FOR TBM (TRAILER BRAKE CONTROL MODULE) DIAGNOSTIC TROUBLE CODES (DTCS)
- Using a diagnostic scan tool, carry out the TBM self-test.
Are there any Diagnostic Trouble Codes (DTCs) present in the TBM?

Yes DIAGNOSE all TBM Diagnostic Trouble Codes (DTCs). GO to DTC Chart: TBM

No GO to B4

B4 CHECK THE TBM (TRAILER BRAKE CONTROL MODULE) OUTPUT

NOTE: Every 4 seconds a voltage pulse is output by the TBM as a trailer connectivity test.

Ignition ON.

Make sure the brake pedal is not being pressed and the manual slider switch is not being applied.

Measure:

Positive Lead	Measurement / Action	Negative Lead
C4099-3	Courtesy of FORD MOTOR COMPANY	Ground

Is steady voltage indicated?

Yes

GO to B5

No	The TBM and vehicle wiring are operating correctly. SEND the trailer to an authorized camper or trailer repair facility.

B5 CHECK THE TBM (TRAILER BRAKE CONTROL MODULE) PWM (PULSE WIDTH MODULATION) OUTPUT CIRCUIT FOR A SHORT TO VOLTAGE

Ignition OFF.

Disconnect TBM C307.

Ignition ON.

Measure:

Positive Lead	Measurement / Action	Negative Lead
C4099-3	Courtesy of FORD MOTOR COMPANY	Ground

Yes	REPAIR the circuit.

No

GO to B6

B6 CHECK FOR CORRECT TBM (TRAILER BRAKE CONTROL MODULE) OPERATION

Inspect TBM C307.

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

Connect TBM C307 and make sure that it seats correctly.

Operate the system and verify 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, INSTALL a new TBM. REFER to: Trailer Brake Control Module (TBM) .

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.