Pinpoint Test AC: The Trailer Battery Charging Is Inoperative/Does Not Operate Correctly

Trailer Lamps

Pinpoint Test AC: The Trailer Battery Charging Is Inoperative/Does Not Operate Correctly

Normal Operation

The trailer battery charge relay coil receives voltage from the Battery Junction Box (BJB) fuse 55 (10A) when the ignition is in the RUN state. The BJB (Battery Junction Box) fuse 90 (25A) supplies voltage to the trailer battery charge relay switch side at all times. When the trailer battery charge relay is energized, the voltage is routed to the trailer tow connector.

This pinpoint test is intended to diagnose the following:

- Fuse

- Wiring, terminals or connectors

- Trailer tow connector

- Trailer battery charge relay

- Trailer

PINPOINT TEST AC : THE TRAILER BATTERY CHARGING IS INOPERATIVE/DOES NOT OPERATE CORRECTLY

NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.

NOTE: Before beginning diagnostics, visually inspect the trailer tow connector mounted on the bumper for signs of corrosion or damage. Repair or install a new trailer tow connector as required.

AC1 CHECK FOR VOLTAGE THROUGH THE TRAILER TOW CONNECTOR (BATTERY CHARGE INOPERATIVE)

- Ignition ON.

- Measure the voltage between the trailer tow connector battery charge voltage supply pin, circuit CAT14 (OG), component side and ground.





Is the voltage greater than 10 volts?

Yes
GO to AC7.

No
VERIFY the BJB (Battery Junction Box) fuse 90 (25A) is OK. If OK, GO to AC2. If not OK, REFER to the Wiring Diagrams to identify the possible causes of the circuit short. [1][2]Diagrams By Number

AC2 CHECK FOR VOLTAGE AT THE TRAILER TOW CONNECTOR (BATTERY CHARGE INOPERATIVE)

- Ignition OFF.

- Disconnect: Trailer Tow C4099.

- Ignition ON.

- Measure the voltage between the trailer tow C4099-5, circuit CAT14 (OG), harness side and ground.





Is the voltage greater than 10 volts?

Yes
INSTALL a new trailer tow connector. TEST the system for normal operation.

No
GO to AC3.

AC3 CHECK THE TRAILER BATTERY CHARGE RELAY (INOPERATIVE CONDITION)

- Ignition OFF.

- Disconnect: Trailer Battery Charge Relay.

- Substitute a known good relay.

- Ignition ON.

- Measure the voltage between the trailer tow C4099-5, circuit CAT14 (OG), harness side and ground.





Is the voltage greater than 10 volts?

Yes
REMOVE the known good relay. INSTALL a new trailer battery charge relay. TEST the system for normal operation.

No
REMOVE the known good relay. GO to AC4.

AC4 CHECK FOR VOLTAGE TO THE BATTERY CHARGE RELAY (SWITCH SIDE)

- Ignition OFF.

- Measure the voltage between the trailer battery charge relay pin 3, SBB90 (YE/RD), BJB (Battery Junction Box) face side and ground.





Is the voltage greater than 10 volts?

Yes
GO to AC5.

No
REPAIR circuit SBB90 (YE/RD) for an open. TEST the system for normal operation.

AC5 CHECK THE TRAILER TOW BATTERY CHARGE RELAY GROUND CIRCUIT FOR AN OPEN

- Measure the voltage between the trailer battery charge relay pin 3, SBB90 (YE/RD), BJB (Battery Junction Box) face side and the trailer battery charge relay pin 2, circuit GD122 (BK), BJB (Battery Junction Box) face side.





Is the voltage greater than 10 volts?

Yes
GO to AC6.

No
REPAIR circuit GD122 (BK) for an open. TEST the system for normal operation.

AC6 CHECK FOR VOLTAGE TO THE TRAILER BATTERY CHARGE RELAY COIL (INOPERATIVE CONDITION)

- Ignition ON.

- Measure the voltage between the trailer battery charge relay pin 1, circuit CBB55 (BN/BU), BJB (Battery Junction Box) face side and ground.





Is the voltage greater than 10 volts?

Yes
REPAIR circuit CAT14 (OG) for an open. TEST the system for normal operation.

No
VERIFY the BJB (Battery Junction Box) fuse 55 (10A) is OK. If OK, REPAIR circuit CBB55 (BN/BU) for an open. TEST the system for normal operation. If not OK, REFER to the Wiring Diagrams to identify the possible causes of the circuit short. [1][2]Diagrams By Number

AC7 CHECK FOR VOLTAGE AT THE TRAILER TOW CONNECTOR (BATTERY CHARGE ALWAYS ON)

- Ignition OFF.

- Measure the voltage between the trailer tow connector battery charge voltage supply pin, circuit CAT14 (OG), component side and ground.





Is any voltage present?

Yes
GO to AC8.

No
The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair facility.

AC8 CHECK THE TRAILER BATTERY CHARGE VOLTAGE SUPPLY CIRCUIT FOR A SHORT TO VOLTAGE

- Disconnect: Trailer Battery Charge Relay.

- Measure the voltage between the trailer tow connector battery charge voltage supply pin, circuit CAT14 (OG), component side and ground.





Is any voltage present?

Yes
REPAIR circuit CAT14 (OG) for a short to voltage. TEST the system for normal operation.

No
GO to AC9.

AC9 CHECK FOR VOLTAGE TO THE TRAILER BATTERY CHARGE RELAY COIL (ALWAYS ON)

- Measure the voltage between the trailer battery charge relay pin 1, circuit CBB55 (BN/BU), BJB (Battery Junction Box) face side and ground.





Is any voltage present?

Yes
REFER to the Wiring Diagrams to identify the possible causes of the circuit short. TEST the system for normal operation. [1][2]Diagrams By Number
No
INSTALL a new trailer battery charge relay. TEST the system for normal operation.