P278C Kick Down Switch Circuit Low

P278C is recorded when the kickdown switch line reads lower than the module allows. No manufacturer documents P278C publicly, and many modern pedals have no electrical kickdown contact at all, as Mazda notes for the 2024 CX-90. On designs with a wired switch the cause is usually the signal pulled to ground: insulation damaged where the harness passes the pedal bracket, a switch contact welded or shorted, or water from the footwell reaching the plug. Depending on the circuit logic the module may then read a permanent kickdown request or none at all. CARB demands such out-of-range checks for inputs. Unlike P278D the signal sits too low, unlike P278B it is not just implausible. Shift behaviour at full throttle becomes unreliable.

Likely causes

Symptoms

• Kickdown always or never active, depending on circuit
• Unexpected downshifts or lack of downshift at full throttle

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

Related codes

References: law.cornell.edu, static.nhtsa.gov.