SureTrack Community Fix: Service Brake System

Real Fixes from Mitchell 1’s SureTrack® expert information resource are documented issues from actual shop repair orders and community discussions. Read on to see how SureTrack can help you correct issues that are not easily diagnosed using OEM information alone. SureTrack is available at no additional cost in our ProDemand product.

When you’re driving along and get a message on your dash saying “Service Brake System”, it’s pretty generic. SureTrack community member eagletireman1 had a Ford Fusion in their shop with this message and also found stored code C109E, but changing the obvious part did not fix the problem. They posed the question to the community, and with the help of fellow community member jhirz and others, they were able to resolve the issue quickly.

The following Community Fix summarizes the interaction between members of the community that led to the solution.

2012 Ford Fusion SEL 3.0L

Code C109E, replaced ABS module.

Customer states that dash reads Service Brake System.

Diagnostic Steps Performed/Parts Replaced
Code C109E (Vacuum Sensor Circuit Failure) stored. Brake booster pressure sensor was replaced. No issue with brake pedal, no hard or falling pedal. Code will sometimes set as soon as you start the vehicle, but at other times must be driven for a while. When I check for power and ground at the sensor I have 5 volts and a good ground. The brown/violet wire is the senor feed wire if the sensor is unplugged. The wire has voltage on it. The voltage is very unsteady, fluctuating from 4.9 to 1.8 volts key on, engine off. Should I have voltage on the sensor wire and should it keep changing.

Best Answer from Community Member jhirz
If you have done those tests as listed, the end result is to replace the ABS module.

Defective ABS module.

Replaced ABS module which solved the problem. Thank you.

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About the Author

Nick Taylor

Nick Taylor is the SureTrack Community Administrator and a Senior Applications Specialist at Mitchell 1 with over 25 years of experience with electronic repair data systems. Nick previously worked in the automotive dismantling and engine rebuilding industries.