Powertrain, generic (extended)

P278A Kick Down Switch Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

P278A is the general circuit fault of the kickdown switch, the contact at the end of accelerator pedal travel that asks the transmission for the lowest possible gear. No manufacturer documents P278A publicly. Many current cars no longer have an electrical switch: Mazda states for the 2024 CX-90 that its kickdown element only adds a felt detent and sends no signal, the pedal position sensor alone deciding. Where a real switch or message exists, the transmission control checks it; Eaton's Endurant HD gearbox logs fault 167 if the kickdown message from the pedal is missing or invalid for 5 s. CARB requires circuit monitoring for such inputs. P278B to P278E name the fault type more precisely. Without the signal, full-throttle downshifts may be weaker or later.

Likely causes

Kickdown switch in or under the pedal defective
Wiring or connector of the pedal module damaged
Kickdown message missing on the data bus (networked designs)

Symptoms

  • No forced downshift at full throttle
  • Reduced acceleration when overtaking

Repair estimate

DifficultyEasyDIY possible
Parts and labour€40–400
Time0.3–1.5 h

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

Parts involved

kickdown switchaccelerator pedalwiring harness

Related codes

P278BP278CP278DP278EP2138

References: law.cornell.edu, static.nhtsa.gov, productinfo.serviceranger4.com.