P278B code meaning
Kick Down Switch Circuit Range/Performance
What P278B means
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.
P278B at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyEasy, DIY possible
- Typical labor0.2 to 1.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P278B
- Kickdown missing at the pedal stop
- Unexpected downshift at part throttle
Common causes of P278B
- Most likelyKickdown switch misadjusted or detent worn
- PossibleFloor mat or object preventing full pedal travel
- Less likelyPedal position sensor offset so that both signals disagree
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Kickdown switchAccelerator pedal
What each part of P278B means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 7 | Area: transmission. |
| 8B | The exact fault in that area. |
What to do next
- Note P278B and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P278B
What does P278B mean?
P278B means "Kick Down Switch Circuit Range/Performance". P278B describes a kickdown switch whose state contradicts the pedal position. It is a generic code, so it means the same on every make.
Is it safe to drive with P278B?
P278B does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will P278B fail an emissions test?
P278B is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is P278B to fix?
Difficulty: easy. A typical repair takes 0.2 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P278B clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.