Powertrain, generic (extended)

P278B Kick Down Switch Circuit Range/Performance

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

P278B describes a kickdown switch whose state contradicts the pedal position. No manufacturer documents P278B publicly. The obvious cross-check is the accelerator pedal sensor: a switch reporting kickdown at part throttle, or staying open although the pedal is pressed to the stop, is implausible. Mazda's 2024 CX-90 bulletin shows how tight the link is, since there the pedal sensor alone defines kickdown and the mechanical detent only gives feel; on cars with a real contact, a worn detent, a misadjusted switch or a floor mat holding the pedal back can create exactly this mismatch. CARB asks for rationality checks on inputs like this. Unlike P278C and P278D the voltage itself is valid. Expect missing or unexpected kickdown shifts.

Likely causes

Kickdown switch misadjusted or detent worn
Floor mat or object preventing full pedal travel
Pedal position sensor offset so that both signals disagree

Symptoms

  • Kickdown missing at the pedal stop
  • Unexpected downshift at part throttle

Repair estimate

DifficultyEasyDIY possible
Parts and labour€0–400
Time0.2–1.5 h

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

Parts involved

kickdown switchaccelerator pedal

Related codes

P278AP278CP278DP278EP2138

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