Pinpoint Test F: DTC P1561
Auxiliary Brake System - Trailer Brake Control (TBC) Module
Pinpoint Tests
Pinpoint Test F: DTC P1561
Refer to Wiring Diagram Set 30, Transmission Controls - TorqShift for schematic and connector information. Diagrams By Number
Normal Operation
The brake fluid pressure transducer supplies a voltage signal to the PCM that varies with the force applied to the brake pedal, more force equals more voltage. The PCM supplies 5 volts to the transducer, this voltage travels through the transducer and then back to the PCM along 2 other circuits, a signal input circuit and a voltage return (or ground) circuit.
- DTC P1561 (Brake Line Pressure Sensor Circuit) - If a short to voltage or an open condition exists on any of the 3 circuits or if the transducer is indicating high pressure for more than 5 seconds while the Brake Pedal Position (BPP) switch (also known as the stoplamp switch) is indicating no brake application, DTC P1561 will be set.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- BPP switch
- Brake fluid pressure transducer
- PCM
PINPOINT TEST F: DTC P1561
NOTICE: Use the Flex Probe Kit for all test connections to prevent damage to the wiring terminals. Do not use standard multi-meter probes.
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F1 CHECK THE PCM BRAKE ON/OFF (BOO1) PID
- Connect the scan tool.
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: DataLogger - PCM .
- Monitor the BOO1 PID while pressing and releasing the brake pedal.
- Does the PID agree with the pedal position?
Yes
GO to F2.
No
REFER to Exterior Lighting Testing and Inspection to continue diagnosis of the stoplamps.
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F2 CHECK THE TRANSDUCER CIRCUITS FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: PCM C175B (gasoline engines) .
- Disconnect: PCM C1551B (diesel engines) .
- Disconnect: PCM C1551E (diesel engines) .
- Disconnect: Brake Pressure Transducer C1025 (all engines) .
- Ignition ON.
- Measure the voltage between ground and:
- brake pressure transducer C1025-1, circuit RE407 (YE/VT), harness side.
- brake pressure transducer C1025-2, circuit LCA16 (GN), harness side.
- brake pressure transducer C1025-3, circuit RCA16 (BU/BN), harness side.
- Is any voltage present?
Yes
REPAIR the affected circuit(s). CLEAR the DTC. REPEAT the self-test.
No
GO to F3.
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F3 CHECK THE TRANSDUCER CIRCUITS FOR A SHORT TO GROUND
- Ignition OFF.
- Measure the resistance between ground and:
- brake pressure transducer C1025-1, circuit RE407 (YE/VT), harness side.
- brake pressure transducer C1025-2, circuit LCA16 (GN), harness side.
- brake pressure transducer C1025-3, circuit RCA16 (BU/BN), harness side.
- Are the resistances greater than 10,000 ohms?
Yes
GO to F4.
No
REPAIR the affected circuit(s). CLEAR the DTC. REPEAT the self-test.
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F4 CHECK THE TRANSDUCER CIRCUITS FOR A SHORT TOGETHER
- Measure the resistance between brake pressure transducer C1025-1, circuit RE407 (YE/VT), harness side and brake pressure transducer C1025-2, circuit LCA16 (GN), harness side.
- Measure the resistance between brake pressure transducer C1025-1, circuit RE407 (YE/VT), harness side and brake pressure transducer C1025-3, circuit RCA16 (BU/BN), harness side.
- Measure the resistance between brake pressure transducer C1025-2, circuit LCA16 (GN), harness side and brake pressure transducer C1025-3, circuit RCA16 (BU/BN), harness side.
- Are the resistances greater than 10,000 ohms?
Yes
GO to F5.
No
REPAIR the affected circuit(s). CLEAR the DTC. REPEAT the self-test.
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F5 CHECK THE TRANSDUCER CIRCUITS FOR AN OPEN
- For vehicles equipped with a gasoline engine, measure the resistance between PCM C175B, harness side and brake pressure transducer C1025, harness side as indicated in the following chart:
- For vehicles equipped with a diesel engine, measure the resistance between PCM C1551B and C1551E, harness side and brake pressure transducer C1025, harness side as indicated in the following chart:
- Are the resistances less than 5 ohms?
Yes
GO to F6.
No
REPAIR the affected circuit(s). CLEAR the DTC. REPEAT the self-test.
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F6 CHECK THE PCM 5 VOLT OUTPUT
- Connect: PCM C175B (gasoline engines) .
- Connect: PCM C1551B (diesel engines) .
- Connect: PCM C1551E (diesel engines) .
- Ignition ON.
- Measure the voltage between brake pressure transducer C1025-2, circuit LCA16 (GN), harness side and ground
- Is the voltage approximately 5 volts?
Yes
INSTALL a new brake pressure transducer. Make sure to LUBRICATE the O-ring seal with clean, specified brake fluid before installation. CLEAR the DTCs. REPEAT the self-test.
No
GO to F7.
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F7 CHECK FOR CORRECT PCM OPERATION
- Disconnect: All PCM Connectors .
- Check the PCM connectors and the brake fluid pressure transducer connector for:
- corrosion.
- spread terminals.
- pushed-out pins.
- Connect: All PCM Connectors .
- Connect: Brake Fluid Pressure Transducer C1025 .
- Make sure the connectors seat properly, then operate the system and verify the concern is still present.
- Is the concern still present?
Yes
INSTALL a new PCM. REFER to Electronic Engine Controls 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. CARRY OUT the self-test with the brake pedal not applied.
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