C0285 GMC - Medium Pressure Accumulator Switch Remains Open
- Faulty Brake Pressure Modulator Valve (BPMV)
- Brake Pressure Modulator Valve (BPMV) harness is open or shorted
- Brake Pressure Modulator Valve (BPMV) circuit poor electrical connection
- Anti-Lock Brake System (ABS) Warning Light ON
- Engine Light ON (or Service Engine Soon Warning Light)
C0285 Gmc DescriptionThe Brake Pressure Modulator Valve (BPMV) contains a Medium Pressure Accumulator (MPA). The MPA provides pressure to the front brakes during certain VSES events. The MPA switch is included to monitor the status of the pressure accumulator. The MPA switch is open when the MPA is uncharged.
The integrity of the MPA switch is tested by the Electronic Brake Control Module (EBCM). The MPA is partially discharged during system initialization to open the switch and then recharged to close the switch. The EBCM continues to monitor the switch to ensure the MPA remains charged. Provided the VSES is not activated, the MPA should remain charged for the entire ignition cycle. If the MPA switch opens within 5 minutes of closing, a fast leak down condition is detected. If the MPA switch opens after 5 minutes has passed, a slow leak down condition is detected.
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