P0406🌫 Emissions / EGR (exhaust gas recirculation) systemDrive with caution, fix soon

P0406: EGR Sensor A Circuit High (Meaning, Causes, Fixes)

Reviewed 2026-10-25 · Based on 2 cited source(s)

What P0406 means

The EGR valve lets a measured amount of exhaust gas back into the cylinders to lower combustion temperatures and cut NOx (oxides of nitrogen) emissions. Most EGR valves have a feedback sensor that tells the PCM the valve's actual position. OBD-Codes.com says this sensor usually reads between about 0.4 and 5 volts, and P0406 may set if it reads abnormally high for too long. RepairPal says P0406 means the EGR valve position sensor is giving voltage readings that are too high, usually above the 4.0 to 4.5 volt range, for example reporting the valve wide open when it should be closed, and that the code can set during normal driving or while the EGR OBD-II monitor runs. The sources differ on symptoms: OBD-Codes.com lists possible surging and intermittent stalling, while RepairPal lists pinging under load and says some drivers notice nothing. RepairPal also notes P0406 is often not a problem with the EGR valve itself. Related codes include P0405 (sensor A circuit low) and P0407 and P0408 (sensor B circuit low and high).

Severity: can I keep driving?

Drive with caution, fix soon

Usually safe to drive for now, but get it diagnosed within a reasonable time. RepairPal rates P0406 Moderate: it may not threaten safety or drivability right away, but it should be fixed to keep the car running well. OBD-Codes.com warns that some cars may surge or stall intermittently, and if the EGR valve is stuck open the engine may stall or not run at all. If your car stalls, get it checked before driving it in traffic. The car will likely fail an emissions test with the light on.

Common symptoms

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

  1. EGR sensor signal circuit shorted to battery voltage (OBD-Codes.com)
  2. EGR sensor signal circuit shorted to the 5 volt reference circuit (OBD-Codes.com)
  3. Open EGR sensor ground circuit or open signal circuit (OBD-Codes.com)
  4. Defective EGR valve position sensor, or its connector or wiring (RepairPal; OBD-Codes.com lists internal failure of the EGR sensor)
  5. Bad EGR valve or solenoid, or a valve sticking open (OBD-Codes.com; RepairPal)
  6. Debris or carbon holding the valve open or keeping it from closing (OBD-Codes.com; RepairPal)
  7. Improper vacuum or electrical signal to the EGR valve, or a bad EGR vacuum supply solenoid (RepairPal)
  8. Bad feedback from the MAP, DPFE (differential pressure feedback EGR) or EGR temperature sensor (RepairPal)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

  1. Read all stored codes with a scan tool and note any other EGR codes (P0400 to P0408) that came with it.
  2. Inspect the EGR valve connector and wiring for chafing, corrosion, loose terminals or broken wires (OBD-Codes.com; RepairPal).
  3. On vacuum-controlled systems, check the vacuum hoses to the EGR valve and solenoid (RepairPal lists improper vacuum).
  4. If the engine starts and stalls, OBD-Codes.com suggests unplugging the EGR valve and restarting; if that helps, a wiring short may be holding the valve open.
  5. Clear the code and see if it returns; OBD-Codes.com says if the scan tool shows normal EGR position, the problem may be intermittent.

Typical fixes

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

  • Comparing actual and desired EGR position on a scan tool with the engine running (OBD-Codes.com)
  • If the reading is 5 volts or higher, checking the signal wire for a short to the 5 volt reference or battery voltage (OBD-Codes.com)
  • Blocking off the EGR port to confirm a stuck-open valve on a car that stalls (OBD-Codes.com)
  • Reviewing freeze frame data and driving to duplicate the setting conditions while watching the position sensor and feedback sensors (RepairPal)
  • Testing position sensor accuracy and DPFE output while raising and lowering the valve (RepairPal)

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Is P0406 serious?

RepairPal rates it Moderate, so it usually isn't an immediate safety issue. OBD-Codes.com says it can cause surging or intermittent stalling, so if your car stalls, have it checked before relying on it in traffic.

Does P0406 mean I need a new EGR valve?

Not always. RepairPal says P0406 is often not a problem with the EGR valve itself, and OBD-Codes.com checks the signal, reference and ground wiring first and replaces the valve only if the wiring checks out.

What is the difference between P0405 and P0406?

Both are about EGR sensor "A". P0405 means the sensor circuit reads low, and P0406 means it reads high, per OBD-Codes.com and RepairPal.

How much does it cost to fix P0406?

Neither source gives a repair cost. It can range from fixing a shorted wire or cleaning carbon to replacing the EGR valve or a sensor, so get a diagnosis and a written estimate first.

Sources

  1. OBD-Codes.com: P0406 Exhaust Gas Recirculation Sensor A Circuit High (Dale Toalston, ASE)
  2. RepairPal: P0406 Exhaust Gas Recirculation Sensor "A" Circuit High (rated Moderate)

Last reviewed 2026-10-25. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.