What it means
The kick-down switch (under the accelerator pedal at full travel) circuit is faulty. The transmission cannot detect the driver's full-throttle downshift request.
At a glance
- Usually lights the check-engine light
How it works
The kick-down switch signals that the accelerator pedal has reached its full-throttle position and the driver is requesting a downshift. P278A sets when the transmission control module detects an electrical fault in the kick-down switch circuit, so the request may not be recognized reliably.
Common causes
Most likely first.
- Switch contacts worn or corroded
- Broken wire to switch
Symptoms
- Check engine or transmission warning light may be on
- Kick-down response may be unavailable or inconsistent
- Delayed downshift during hard acceleration
How to diagnose it
- Save freeze-frame data and check whether the kick-down switch state changes on the scan tool as the accelerator is pressed through its full travel.
- Inspect the switch under or near the accelerator pedal for damage, contamination, loose mounting, or a pedal obstruction.
- Check the switch connector and wiring for corrosion, loose terminals, breaks, or chafing along the route to the transmission control module.
- Test switch continuity or signal changes while operating the pedal, following the manufacturer's wiring diagram and specification.
- If the switch signal is correct at the switch but not at the module, test the intervening circuit and module connector for an open or poor connection.
Common fixes
- Remove an obstruction and ensure the accelerator pedal reaches full travel.
- Clean or repair corroded or loose kick-down switch terminals.
- Repair an open or damaged wire in the kick-down switch circuit.
- Replace the kick-down switch if its contacts fail the specified test.
Can I keep driving?
Normal acceleration is usually possible, but the transmission may not downshift when you request full power. Avoid relying on kick-down for merging or passing until repaired, and leave extra room for acceleration.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.