Pinpoint Test Y: The Trailer Lamps Are Inoperative

WARNING: This page is about a different car, the 2006 Mercury Mariner and 2006 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.

Y1 DETERMINE THE CONDITION
- Key in ON position.
- Place the multifunction switch in the parking lamps ON position.
- Apply and release the brake pedal while observing the trailer lamps.
- Are all the trailer tow lamps inoperative?
Yes: REPAIR circuit 57 (BK). TEST the system for normal operation.

No: If the trailer parking lamps are inoperative, PLACE the multifunction switch in the OFF position. GO to Y2.

If a trailer stoplamp is inoperative, PLACE the multifunction switch in the OFF position. GO to Y4.
Y2 CHECK VOLTAGE TO THE TRAILER TOW CONNECTOR
- Key in OFF position.
- Disconnect: Trailer Tow C439.
- Key in ON position.
- Turn the multifunction switch in the parking lamps ON position.
- Measure the voltage between the trailer tow C439-3, circuit 962 (BN/WH), harness side and ground.
  
  Fig 1: Checking Voltage To Trailer Tow Connector
  Courtesy of FORD MOTOR CO.
- Is the voltage greater than 10 volts?
Yes: The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair center.

No: VERIFY the SJB fuse 1 (15A) is OK. If OK, PLACE the multifunction switch in the OFF position. GO to Y3
Y3 CHECK CIRCUIT 962 (BN/WH) FOR AN OPEN OR SHORT TO GROUND
- Key in OFF position.
- Disconnect: SJB C2280c.
- Measure the resistance between the SJB C2280c-15, circuit 962 (BN/WH), harness side and the trailer tow C439-3, circuit 962 (BN/WH), harness side; and between the SJB C2280c-15, circuit 962 (BN/WH), harness side and ground.
  
  Fig 2: Checking Circuit 962 (BN/WH) For An Open Or Short To Ground
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms between the SJB and the trailer tow connector, and greater than 10,000 ohms between the SJB and ground?
Yes: GO to Y6.

No: REPAIR the circuit. RUN the on-demand self-test (required to clear certain DTCs). CORRECT any unresolved DTCs. CLEAR all DTCs. TEST the system for normal operation.
Y4 CHECK THE VOLTAGE TO THE TRAILER TOW CONNECTOR
- Key in OFF position.
- Disconnect: Trailer Tow C439.
- While applying the brake pedal, measure the voltage between the trailer tow C439-1, circuit 64 (DG), harness side and ground; or between the trailer tow C439-2, circuit 52 (YE), harness side and ground.
  
  Fig 3: Checking Voltage To Trailer Tow Connector
  Courtesy of FORD MOTOR CO.
- Is the voltage greater than 10 volts?
Yes: The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair center.

No: GO to Y5.
Y5 CHECK THE TRAILER TOW CIRCUITRY
- Disconnect: SJB C2280c.
- If the RH trailer tow stoplamp is inoperative, measure the resistance between the SJB C2280c-24, circuit 64 (DG), harness side and the trailer tow C439-1, circuit 64 (DG), harness side; and between the SJB C2280c-24, circuit 64 (DG), harness side and ground.
  
  Fig 4: Checking Trailer Tow Circuitry (1 Of 2)
  Courtesy of FORD MOTOR CO.
- If the LH trailer tow stoplamp is inoperative, measure the resistance between the SJB C2280c-12, circuit 52 (YE), harness side and the trailer tow C439-2, circuit 52 (YE), harness side; and between the SJB C2280c-12, circuit 52 (YE), harness side and ground.
  
  Fig 5: Checking Trailer Tow Circuitry (2 Of 2)
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms between the SJB and the trailer tow connector, and greater than 10,000 ohms between the SJB and ground?
Yes: GO to Y6.

No: REPAIR the circuit in question. RUN the on-demand self-test (required to clear certain DTCs). CORRECT any unresolved DTCs. CLEAR all DTCs. TEST the system for normal operation.
Y6 CHECK FOR CORRECT SJB OPERATION
- Disconnect all the SJB connectors.
- Check for:
  - corrosion
  - pushed-out pins
- Connect all the SJB connectors and make sure they seat correctly.
- Operate the system and verify the concern is still present.
- Is the concern still present?
Yes: INSTALL a new SJB. REFER to SMART JUNCTION BOX (SJB) . TEST the system for normal operation.

No: The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test.