P278D code meaning
Kick Down Switch Circuit High
What P278D means
P278D means the kickdown switch circuit shows a voltage above its permitted maximum. No manufacturer documents P278D publicly. With the usual pull-up input this is the reading of an interrupted line: the pedal module unplugged after a repair, a broken wire at the hinge of a floor-mounted pedal, or a missing ground at the switch. A short to battery voltage produces the same picture but is rarer. For networked pedals the comparable case is a message that is missing or flagged as invalid, as Eaton describes for the kickdown signal of its Endurant HD gearbox (fault 167, 5 s). CARB requires out-of-range checks on such inputs. P278C is the low-voltage twin. Kickdown requests are lost until the circuit is restored.
P278D at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyEasy, DIY possible
- Typical labor0.3 to 1.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P278D
- No kickdown at full throttle
- Slower acceleration from speed
Common causes of P278D
- Most likelyOpen signal or ground wire, pedal module unplugged
- PossibleWire broken by pedal movement
- Less likelySignal wire shorted to battery voltage
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Kickdown switchWiring harness
What each part of P278D 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. |
| 8D | The exact fault in that area. |
What to do next
- Note P278D 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 P278D
What does P278D mean?
P278D means "Kick Down Switch Circuit High". P278D means the kickdown switch circuit shows a voltage above its permitted maximum. It is a generic code, so it means the same on every make.
Is it safe to drive with P278D?
P278D does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will P278D fail an emissions test?
P278D 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 P278D to fix?
Difficulty: easy. A typical repair takes 0.3 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P278D clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.