OBD-II Code · Emissions
P0406
EGR Sensor A Circuit High
Severity
low
Lowest on our scale. Fix it when convenient.
Can you drive it
Only if running normally
A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety.
Indicative cost (USD)
$100–$400
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
EGR sensor voltage high.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
Likely causes
- Failed sensorMost common
- Wiring short to power
Read the full diagnostic procedureP0406 is the high-side counterpart to P0405 — the EGR position sensor A signal is reading high, above the maximum voltage threshold the ECM expects,…
P0406 is the high-side counterpart to P0405 — the EGR position sensor A signal is reading high, above the maximum voltage threshold the ECM expects, typically above 4.8V on a 0-5V sensor. The fault is signal-wire shorted to the 5V reference internally in the sensor, externally in the harness, or the sensor's wiper has lost contact with its resistor track and is floating at supply voltage.
Diagnostic ladder
- backprobe the position sensor signal pin at rest and read voltage — anything above 4.5V with the valve commanded closed is a fault.
- Unplug the sensor connector with the ignition on; if signal voltage at the harness side drops to a normal floating value (typically 2.5V or so on a pulled-up circuit), the sensor itself is shorted internally — replace it.
- If signal voltage stays pegged at 5V with the sensor unplugged, the short is in the harness between the sensor and the ECM — inspect for chafed insulation against the engine, manifold, or strut tower.
- Carbon-bound valves can also drive P0406 if the pintle is jammed in the fully-open position and the position sensor honestly reports max travel — pull the valve and verify mechanical freedom before condemning the sensor electrically.
- On vehicles with a separate EGR position sensor (not integrated into the valve), the sensor is replaceable by itself for $40-$80; on integrated-sensor valves (most GM linear EGR), the whole assembly goes.
Vehicle-specific patterns2003-2010 GM 3.5/3.9L V6 and 4.8/5.3L truck V8s throw P0406 from the same integrated-sensor failure pattern as P0405 — the internal wiper loses conta…
- 2003-2010GM 3.5/3.9L V6 and 4.8/5.3L truck V8s throw P0406 from the same integrated-sensor failure pattern as P0405 — the internal wiper loses contact and reads pulled-up high; whole valve replaces.
- 2000-2007Chrysler/Dodge 3.3/3.8L V6 minivan throws P0406 from a stuck-open carbon-coked valve combined with an honest high-position reading — clean or replace the valve, the sensor itself is fine.
- 2002-2009Ford 4.6L 2V (Crown Vic, Mustang) throws P0406 from a chafed EGR sensor harness against the upper intake — wrap the chafe point and the code clears.
- 2005-2012Nissan Pathfinder/Frontier VQ40DE throws P0406 from corrosion in the EGR position sensor connector where it picks up engine-bay moisture — clean pins, dielectric-grease, and verify the code stays gone.
Estimated repair$30 (harness fix) to $250+ (full valve replacement).
Look up another code
P0406 — frequently asked
What does a P0406 code mean?
EGR sensor voltage high.
What causes a P0406 code?
Common causes: Failed sensor; Wiring short to power.
What are the symptoms of a P0406 code?
Typical symptoms: Check engine light.
Is it safe to drive with a P0406 code?
Only if running normally. A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety. Estimated repair: $100-$400.
How do I diagnose a P0406 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
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