P0405: EGR sensor circuit reading low
Exhaust gas recirculation sensor A circuit low
Severity: Monitor
P0405 is an electrical fault in the EGR sensor circuit; MechanicBase rates it low severity with usually no drivability change, though it will fail an emissions test.
It gets more serious if:
- Inspect soon: Have it inspected soon if the engine idles unevenly, pings or loses power, which TaT and MechanicBase list as possible effects.
P0405 in short
P0405 means the EGR sensor is sending the engine computer a voltage lower than expected. The usual causes are the sensor in the EGR valve, damaged wiring or a loose connector. The car normally drives as usual, but the light stays on and the car will not pass an emissions test until it is fixed.
Many EGR valves have a position sensor so the computer knows how far the valve is open. On some vehicles the sensor is a pressure sensor that measures flow instead.
P0405 sets when that sensor voltage is below its allowed range, which TaT says reflects a short to ground, a faulty sensor or wiring problems.
Because it is an electrical code, wiring and connectors are cheaper to check than the valve itself.
Most likely causes
These are general causes for this code across vehicles. None is specific to one make or model.
Cause 1: Damaged wiring or loose connector at the EGR valve
Common general cause- Why it ranks here
- TaT and MechanicBase both name short-to-ground and wiring faults, and MechanicBase says to check connectors before replacing parts.
- What would change this
- Rises if a connector is loose, corroded or a wire is chafed. Falls if wiring tests good.
Cause 2: EGR position or flow feedback sensor failed
Common general cause- Why it ranks here
- MechanicBase lists the EGR position sensor and differential-pressure feedback sensor as primary causes.
- What would change this
- Rises if the sensor voltage stays low with good wiring. Falls if the voltage changes when the valve moves.
Cause 3: Defective EGR valve (sensor built in)
Common general cause- Why it ranks here
- On many vehicles the position sensor is part of the valve, so a failed valve gives the same code.
- What would change this
- Rises if the sensor is not sold separately and tests bad. Falls if the sensor reading follows commands.
Cause 4: Engine computer fault
Possible — needs testing- Why it ranks here
- MechanicBase says this is rare and ranks it last.
- What would change this
- Rises only after every other part and wire tests good.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: Read stored codes and the live EGR sensor voltage with a scan tool.
IfThe voltage stays near its lowest value even when the valve is commanded
It meansCheck the wiring, then the sensor.
IfThe voltage changes normally
It meansThe fault may be intermittent; wiggle-test the harness.
Step 2: Inspect the EGR connector and wiring for damage, corrosion or loose pins.
IfDamage or a loose connector is found
It meansRepair it and retest.
Points to: Damaged wiring or loose connector at the EGR valve
IfWiring is fine
It meansThe sensor or valve is suspect.
Symptoms
- Check engine light, often the only sign
- Failed emissions test
- Uneven idle, pinging or reduced power Gets more serious: stop and have it checked.
How to fix
Step 1: With the engine off and cool, check that the EGR valve connector is fully clipped in.
Parts and cost context
- Engine control module (ECM / PCM):Treated as a last resort. Labour varies; get a quote.
Labor varies by vehicle and shop; get a quote before you approve a repair.
Compare used part prices on PartPriceGuideOn your vehicle
We don't have reviewed vehicle-specific evidence for P0405 yet. The causes and tests above apply across vehicles.
Related codes
No curated relationships for P0405 yet.
P0405 questions
Can I drive with P0405?
Usually yes. MechanicBase notes the car typically has no drivability problem, but the car will not pass emissions testing until fixed.
Sources and review
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error