Rick's Free Auto Repair Advice

C027B Low Brake Pedal

Why are you getting a C027B Low Brake Pedal code after replacing a master cylinder


GM has issued a service bulletin #PI0785B to address a C027B code that appears after replacing a master cylinder on the vehicles listed below. GM says the C027B trouble code is most likely due to a missing O-ring that fell off during the master cylinder replacement procedure. The missing O-ring master cylinder o ringresults in a vacuum leak between the vacuum brake booster and the master cylinder causing a low brake pedal and the trouble code.

To prevent the problem from happening again, GM recommends bleeding the booster vacuum by pumping the brake pedal or pulling the check valve out of the booster before removing the master cylinder. The residual vacuum suction may be the culprit that dislodges the O-ring when pulling the master cylinder out.

2009-2014 Buick Enclave

2010-2012 Buick LaCrosse

2011-2014 Buick Regal

2012-2014 Buick Verano

2013-2014 Buick Encore

2009-2014 Cadillac CTS, SRX

2013-2014 Cadillac ATS, XTS

2009-2012 Chevrolet Colorado

2009-2014 Chevrolet Corvette, Impala, Malibu, Traverse

2010-2014 Chevrolet Camaro, Equinox

2011-2014 Chevrolet Cruze

2012 Chevrolet Captiva Sport

2012-2014 Chevrolet Sonic

2013-2014 Chevrolet Spark

2009-2012 GMC Canyon

2009-2014 GMC Acadia

2010-2014 GMC Terrain

Posted on by Rick Muscoplat

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