What it means
Same as P05F3 with the control line 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
- Affects emissions; the car can fail an emissions test
How it works
The exhaust aftertreatment power relay control circuit tells the relay when to supply power to emissions-control equipment. The control module sets P05F5 when voltage on that control line is higher than expected, often because the line is shorted to a supply. It does not confirm that every aftertreatment component is powered continuously.
Common causes
Most likely first.
- Control line shorted to supply
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
Symptoms
- Check-engine light or emissions warning may illuminate
- Aftertreatment system fault message may appear
How to diagnose it
- Record freeze-frame data and compare the relay command with live control-line status to determine when the high reading occurs.
- Inspect the relay control harness for pinched or chafed insulation touching a power feed, and check connectors for moisture or terminal damage.
- Check the relay socket and nearby wiring for incorrect connections or evidence of heat damage.
- Measure the control line at the relay and module during commanded on and off states, following the wiring diagram.
- If the high voltage remains, isolate the circuit as specified and test for a short to supply before condemning the relay or module.
Common fixes
- Repair a control wire shorted to a supply source.
- Repair damaged, corroded, or wet relay control connector terminals.
- Replace a relay confirmed to have an internal control fault.
- Repair a confirmed module output fault after the harness tests correctly.
Can I keep driving?
The vehicle may remain driveable, but incorrect relay control can disrupt power to aftertreatment equipment and emissions control. Avoid prolonged driving if warnings appear or worsen, and follow any countdown or starting restriction message.
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.