P0405 code: Exhaust Gas Recirculation Sensor A Circuit Low
P0405 means exhaust Gas Recirculation Sensor A Circuit Low. The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0405 means
P0405 means the sensor that reports the EGR valve's position is sending a lower voltage than the computer ever expects to see. The EGR system recirculates a small amount of exhaust back into the intake to cool combustion and cut NOx emissions, and the computer relies on this position sensor to know how far the valve is actually open. A constant low reading usually points to a failed position sensor, a wiring short to ground, or a bad connection rather than a mechanical EGR problem. On many engines the sensor is built into the EGR valve itself, so fixing it can mean replacing the whole valve. If the computer can't trust the position reading it may limit or disable EGR, which can cause light pinging under load and a failed emissions test. It's an electrical-circuit code, so checking the wiring and connector before buying parts is worthwhile.
P0405 symptoms
- Check-engine light, often with little change in how the car drives
- Possible pinging or knocking under acceleration if EGR is disabled
- Rough idle or hesitation on some engines
- Failed emissions test
What it costs to fix P0405
Varies by vehicle — get it diagnosed.
The repair cost for this code depends too much on your exact vehicle and the underlying cause to quote a meaningful range. Confirm the cause first so you only pay for the fix you actually need.
Diagnose P0405 for my vehicle →How to fix P0405
Moderate — doable at home with common tools and patience
- Scan for other 5-volt sensor codes
Note whether MAP, throttle position, or other sensor-low codes are stored alongside P0405. Several low codes at once usually means a shared 5-volt reference is being dragged down by one shorted sensor or wire — find that and the EGR code often clears without touching the valve.
- Inspect the EGR valve connector and nearby harness
The valve sits in a hot, sooty spot, often right beside the EGR tube. Look for a cracked connector body, green corrosion, oil or carbon inside the terminals, and insulation baked brittle by exhaust heat. A wire rubbed through against the engine or a bracket is a typical circuit-low cause.
- Measure reference, ground, and signal at the plug
Key on, engine off, back-probe the connector: the reference wire should show close to 5 volts and the ground should read near zero against battery negative. A healthy position signal rests low but clearly above zero with the valve shut; a signal sitting at or very near zero volts confirms the fault the computer is seeing.
- Jumper the signal to separate sensor from wiring
Unplug the valve and use a fused jumper to briefly connect the harness signal pin to the reference pin while watching the EGR position reading on a scan tool. If the reading jumps to its maximum, the wiring and computer are fine and the sensor has failed; if it stays low, the signal wire is shorted or broken on the way back.
- Replace the valve or sensor and verify it tracks
Where the position sensor is built into the EGR valve, the valve is replaced as an assembly with a new gasket; on some engines the sensor unbolts separately. If the pintle is carbon-bound, clean the port while the valve is off. Afterward, command the EGR open with a scan tool and confirm the position reading follows the command.
DIY or shop? Everything up to the jumper test needs only a multimeter, back-probe pins, and a scan tool that shows EGR position, so a home mechanic can usually find out whether this is a wire or a part before spending anything. Swapping a bolt-on EGR valve is ordinary wrenching, though exhaust-heated bolts can be stubborn. It becomes shop work when the short to ground hides deep in the engine harness, when the valve is buried under intake plumbing, or when your vehicle needs a scan-tool learn procedure for the new valve.
Tools for the DIY steps: Digital multimeter · Back-probe pins · Fused jumper lead · Scan tool that displays EGR position · Basic socket set · Penetrating oil
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0405.
Start a case with P0405 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0405?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0405: common questions
Can I drive with P0405?
The code by itself can't answer that. You may not notice much change, but if the computer disables EGR you may get pinging under acceleration, which causes engine wear over time. Plan a repair soon rather than ignoring it.
Do I need a whole new EGR valve for P0405?
It depends on your engine. On many vehicles the position sensor is built into the EGR valve, so the valve gets replaced as a unit. On others the sensor is separate and cheap. A wiring or connector problem is also possible, so diagnose before buying parts.
What does the EGR position sensor actually do?
It tells the computer how far the EGR valve is open, so the computer can verify the valve is doing what it commanded. P0405 means that feedback signal is stuck low — the computer no longer trusts it, not necessarily that the valve itself is broken.
Will P0405 fail an emissions test?
Almost certainly — in areas with OBD-based testing, an active check-engine light is typically an automatic fail, and EGR faults are emissions-related by definition. Fix the code and complete a few drive cycles before testing.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0405 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0405 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.