What it means
Same as P05C7 with the signal shorted to supply. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
How it works
The economy-mode switch sends the driver's ECO request to the control module through a signal circuit. P05CA sets when that signal is higher than expected, often because the signal is shorted to a supply voltage or the connector has a poor contact.
Common causes
Most likely first.
- Signal shorted to supply
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
Symptoms
- Check-engine light
- Economy mode may not respond to the switch
- Economy mode may be unavailable or remain selected
How to diagnose it
- Save freeze-frame data and watch live ECO switch status while operating the switch to determine whether the input is stuck or fails to follow the button.
- Inspect the switch connector and harness for pinched or chafed wires, moisture, corrosion, or terminals that have backed out.
- Gently move the harness while monitoring switch status to help locate an intermittent short or connection fault.
- Use the wiring diagram to check the signal circuit for a short to supply and inspect terminal contact for excessive resistance.
- If the circuit checks out, test switch output against the manufacturer's specification before replacing the switch.
Common fixes
- Repair a signal wire pinched against a power source or damaged by chafing.
- Clean and secure corroded or loose switch terminals.
- Replace a damaged connector or terminal that cannot maintain contact.
- Replace the economy-mode switch if it produces an out-of-range signal with a sound circuit.
Can I keep driving?
Driving is generally possible if the vehicle behaves normally, since the code concerns economy-mode selection. The mode may not respond correctly or could appear stuck, affecting throttle response, shifting, or climate operation.
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.