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Pinpoint Test H: DTC C1446




Anti-Lock Control

Pinpoint Tests

Pinpoint Test H: DTC C1446

Refer to Wiring Diagram Set 42, Vehicle Dynamic Systems for schematic and connector information. Diagrams By Number

Normal Operation

The ABS module monitors the brake pressure transducer in combination with other brake inputs: wheel speed sensors, stoplamp switch from the PCM over the High Speed Controller Area Network (HS-CAN) bus and lateral accelerometer from the sensor cluster. The pressure transducer signal is used by the ABS module for various diagnostic routines as well as to determine system functionality. The pressure transducer is located inside the Hydraulic Control Unit (HCU) and can be monitored via the master cylinder pressure (MC_PRESS) PID. The PID should correlate closely with system hydraulic pressure. When the vehicle is at rest without input from the brake pedal, this PID value should be at or close to 0 kPa (0 psi). However, due to factors such as vehicle age or minor discrepancies in manufacturing, PID readings may have some variability. If the transducer signal reads above 620 kPa (90 psi) when other inputs indicate the system should not be pressurized, DTC C1288 will be set. If the transducer requires service, a new HCU must be installed.

- DTC C1288 (Pressure Transducer Main/Primary Input Circuit Failure) - If during the ABS module self-test or normal operation the ABS module detects an open, a short to voltage or a short to ground in the transducer, DTC C1288 will be set. Also, if the transducer input does not match the information received from other sources, DTC C1288 will be set.

This pinpoint test is intended to diagnose the following:
- Brake pedal binding
- Air in the brake hydraulic system
- Fluid leak in the brake hydraulic system
- HS-CAN bus
- Stoplamp switch
- HCU

PINPOINT TEST H: DTC C1446

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H1 CHECK THE RED BRAKE WARNING INDICATOR


- Observe the red brake warning indicator while turning the ignition switch from OFF to RUN.
- Ignition ON.
- Does the indicator illuminate for a short time and then go out?

Yes
GO to H2.

No
If the red brake warning indicator remains illuminated or does not illuminate at all, GO to Instrument Panel, Gauges and Warning Indicators to diagnose the red brake warning indicator.

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H2 CHECK THE ABS MODULE MASTER CYLINDER PRESSURE (MC_PRES) PID


NOTE: To obtain the most accurate reading, it is recommended to use a graph display for this PID.

NOTE: The initial pressure reading may be greater than 0. This is a normal condition. If the pedal is not pressed slowly, an initial spike may occur.

- Connect the scan tool.
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: DataLogger - ABS Module.
- Monitoring the MC_PRES PID, make a note of the initial master cylinder pressure.
- Steadily press and release the brake pedal while monitoring the ABS module MC_PRES PID.
- Does the PID smoothly increase with increased brake pedal pressure and smoothly decrease with decreased brake pedal pressure, without any spikes, and does the final pressure match the recorded pressure within 0.5 psi?

Yes
GO to H3.

No
GO to Pinpoint Test G. Pinpoint Test G: DTC C1288

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H3 CHECK FOR COMMUNICATION DTCs


- Review the DTCs retrieved and recorded during Inspection and Verification.
- Are DTCs U0073 or U0115 present?

Yes
REFER to Information Bus to diagnose the HS-CAN bus.

No
GO to H4.

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H4 MONITOR THE ABS MODULE BRAKE ON/OFF (BOO_ABS) PID


- Enter the following diagnostic mode on the scan tool: DataLogger - ABS Module.
- Monitor the BOO_ABS PID, while pressing and releasing the brake pedal.
- Does the PID agree with the brake pedal position?

Yes
The system is operating correctly at this time. TEST DRIVE the vehicle above 32 km/h (20 mph) and CARRY OUT at least one ABS stop. RETRIEVE and RECORD any DTCs.

No
GO to H5.

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H5 MONITOR THE PCM BRAKE PEDAL POSITION (BOO) PID


- Enter the following diagnostic mode on the scan tool: DataLogger - PCM.
- Monitor the BOO PID, while pressing and releasing the brake pedal.
- Does the PID agree with the brake pedal position?

Yes
The system is operating correctly at this time. TEST DRIVE the vehicle above 32 km/h (20 mph) and CARRY OUT at least one ABS stop. RETRIEVE and RECORD any DTCs.

No
Using the scan tool, CARRY OUT the Key ON Engine Running (KOER) self-test. REFER to Computers and Control Systems Information to diagnose the DTC retrieved.

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