CarScan
C0040Chassis

C0040: brake pedal switch in the standard, front right wheel at GM

Where to start

⛔ Here the readings differ not by wheel but by PART. Under SAE J2012 the number C0040 means the brake pedal switch, while in the GM numbering it is the front right wheel speed sensor. Different parts at opposite ends of the car. So first work out whose code it is: the make and the module that reported it. If it is the brake switch — check whether the brake lights come on; with a bad switch, cruise control often will not engage and an automatic will not leave «park». If it is the wheel — the connector and the wire at the hub, sensor last.

A code is not a diagnosis. It says which check failed, not which part to replace. Clearing it without repair only means the car will report it again in a few trips.

How to put together a report a mechanic will actually read

We have a detailed piece on thisWhy a scanner does not show ABS, airbag and gearbox faults

How the code is built

Letter — the systemChassis: brakes, ABS, suspension
Common or the maker's ownGeneric code: the same on every car
Number of the faultThe serial number inside that group — it does not say how serious the fault is

All codes in «Brakes, ABS and stability control»

How the app helps

CarScan reads this code from your car through an OBD-II adapter, shows whether it is active now or only stored, names the module that reported it, and puts it into a plain-text report for your mechanic.

See what the app does

Unfamiliar word? Open the glossary

What the letter and the four digits mean