Pinpoint Test C: DTCs C2797 and C2798
Auxiliary Brake System - Trailer Brake Control (TBC) Module
Pinpoint Tests
Pinpoint Test C: DTCs C2797 and C2798
NOTE: Carry out all pinpoint tests without a trailer connected to the vehicle.
Refer to Wiring Diagram Set 95, Trailer/Camper Adapter for schematic and connector information. Diagrams By Number
Normal Operation
The brake pressure transducer is attached to the brake master cylinder and is hardwired to the Trailer Brake Control (TBC) module. The transducer can be serviced separately from the master cylinder. The TBC module supplies voltage to the transducer along circuit LCA16 (GN) and ground along circuit RCA16 (BU/BN). The voltage returned from the transducer along circuit VCA13 (YE/BU) is used by the TBC module to determine current brake pressure.
- DTC C2797 (Brake Pressure Transducer Supply Short to Battery) - With the ignition switch in the RUN position, if the TBC detects more than 5.5 volts on circuit LCA16 (GN) for 200 ms or more, the TBC module will no longer use the pressure transducer input.
The TBC module will also set DTC C2797, send TRAILER BRAKE MODULE FAULT to the message center and revert to a limited operating strategy.
- DTC C2798 (Brake Pressure Transducer Supply Short to Ground) - With the ignition switch in the RUN position, if the TBC detects less than 4.5 volts on circuit
LCA16 (GN) for 200 ms or more, the TBC module will no longer use the pressure transducer input. The TBC module will also set DTC C2798, send TRAILER BRAKE MODULE FAULT to the message center and revert to a limited operating strategy.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- Brake pressure transducer
- TBC module
PINPOINT TEST C: DTCs C2797 AND C2798
NOTICE: Use the Flex Probe Kit for all test connections to prevent damage to the wiring terminals. Do not use standard multi-meter probes.
NOTE: If there is no brake pressure transducer mounted on the brake master cylinder, then the system was not correctly installed. Warranty repairs on incorrectly installed trailer brake systems will not be covered by Ford Motor Company.
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C1 CHECK FOR TBC MODULE ON-DEMAND DTCs
- Connect the scan tool.
- Ignition ON.
- Using the scan tool, clear the DTCs.
- Ignition OFF.
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: Self Test - TBC Module .
- Retrieve and record the DTCs.
- Did DTC C2797 or C2798 return?
Yes
GO to C2
No
If other DTCs are retrieved, GO to the Trailer Brake Control (TBC) Module DTC Chart. Diagnostic Trouble Code Tests and Associated Procedures
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C2 CHECK THE TBC MODULE OUTPUT TO THE BRAKE PRESSURE TRANSDUCER
- Ignition OFF.
- Disconnect: Brake Pressure Transducer C147 .
- Ignition ON.
- Measure the voltage between brake pressure transducer C147-3, circuit LCA16 (GN), harness side and brake pressure transducer C147-1, circuit RCA16 (BU/BN) harness side.
- Is the voltage between 4.5 and 5.5 volts?
Yes
CONNECT C147 and attempt to recreate the DTC by flexing the wire harness at the brake pressure transducer. If the DTC returns, REPAIR circuit LCA16 (GN). CLEAR the DTCs. REPEAT the self-test. If the DTC does not return, CHECK the brake pressure transducer connector for corrosion, pushed-out pins and spread terminals. REPAIR the brake pressure transducer connector as necessary. CLEAR the DTCs. REPEAT the self-test.
No
If the voltage is greater than 5.5 volts, GO to C3.
If the voltage is less than 4.5 volts, GO to C4.
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C3 CHECK THE BRAKE PRESSURE TRANSDUCER SUPPLY CIRCUIT FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: TBC Module C2142 .
- Ignition ON.
- Measure the voltage between brake pressure transducer C147-3, circuit LCA16 (GN), harness side and ground.
- Is any voltage present?
Yes
REPAIR circuit LCA16 (GN). CLEAR the DTCs. REPEAT the self-test.
No
CONNECT C147 and C2142, ATTEMPT to recreate the DTC by flexing the wire harness at the brake pressure transducer. If the DTC returns, REPAIR circuit LCA16 (GN). CLEAR the DTCs. REPEAT the self-test. If the DTC does not return, CHECK the brake pressure transducer connector for corrosion, pushed-out pins and spread terminals. REPAIR the brake pressure transducer connector as necessary. CLEAR the DTCs. REPEAT the self-test. If the connectors are OK, GO to C7.
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C4 CHECK THE BRAKE PRESSURE TRANSDUCER SUPPLY CIRCUIT FOR A SHORT TO GROUND
- Ignition OFF.
- Disconnect: TBC Module C2142 .
- Measure the resistance between TBC module C2142-6, circuit LCA16 (GN), harness side and ground.
- Is the resistance greater than 10,000 ohms?
Yes
GO to C5.
No
REPAIR circuit LCA16 (GN). CLEAR the DTCs. REPEAT the self-test.
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C5 CHECK THE BRAKE PRESSURE TRANSDUCER SUPPLY CIRCUIT FOR AN OPEN
- Measure the resistance between TBC module C2142-6, circuit LCA16 (GN), harness side and brake pressure transducer C147-3, circuit LCA16 (GN), harness side.
- Is the resistances less than 5 ohms?
Yes
GO to C6.
No
REPAIR circuit LCA16 (GN). CLEAR the DTCs. REPEAT the self-test.
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C6 CHECK THE BRAKE PRESSURE TRANSDUCER FOR A SHORT
- Measure the resistance between brake pressure transducer C147, pin-1, component side and brake pressure transducer C147, pin-3, component side while firmly pressing and releasing the brake pedal.
- Is the resistance less than 5 ohms?
Yes
INSTALL a new pressure transducer. Make sure to LUBRICATE the O-ring with clean, specified brake fluid before installation. CLEAR the DTCs. REPEAT the self-test.
No
CONNECT C147 and C2142, ATTEMPT to recreate the DTC by flexing the wire harness at the brake pressure transducer. If the DTC returns, REPAIR circuit LCA16 (GN). CLEAR the DTCs. REPEAT the self-test. If the DTC does not return, CHECK the brake pressure transducer connector for corrosion, pushed-out pins and spread terminals. REPAIR the brake pressure transducer connector as necessary. CLEAR the DTCs. REPEAT the self-test. If the connectors are OK, GO to C7.
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C7 CHECK FOR CORRECT TBC MODULE OPERATION
- Check the TBC module connector for:
- corrosion.
- pushed-out pins.
- spread terminals.
- Connect the TBC module connector and make sure that it is seated correctly.
- Operate the system and verify the concern is still present.
- Is the concern still present?
Yes
INSTALL a new TBC module. REFER to Trailer Brake Control (TBC) Module Service and Repair. CLEAR the DTCs. REPEAT the self-test.
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.
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