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Home / Codes / P0406
DTC code page

P0406: Exhaust Gas Recirculation Sensor A Circuit High

Quick answer: The EGR feedback signal is reading higher than expected, often because of a biased sensor, signal short to voltage, or valve-position reporting fault.

Drivers also search this fault as EGR sensor high, EGR position sensor high voltage, EGR feedback circuit high.

Severity: medium Family: powertrain Related paths: 9
Meaning

What P0406 usually means

P0406 is the high-voltage mirror image of P0405. The ECU is seeing an EGR position or feedback signal that is higher than the expected range, which can happen when the sensor is biased upward, the signal circuit is shorted to voltage, the reference and ground relationship is corrupted, or the valve is physically not where the module thinks it should be. The diagnosis lives in signal integrity and true valve position, not in guessing based on the code alone.

Fast triage

Start here before chasing parts

  • Scan first: save freeze-frame and pending codes before clearing anything.
  • Confirm the complaint: compare the stored code with current drivability symptoms.
  • Use context: trims, live data, and related codes usually narrow the fault faster than guesswork.
  • Work simplest to hardest: leaks, connectors, maintenance items, and known patterns before expensive components.
Initial checks

What to check first

  • Do not assume the valve is actually wide open; first see whether the high reading is believable in live data.
  • Inspect the harness and connector because signal-high faults often come from rubbed wiring or pin damage.
  • Check whether the engine also has rough idle or surge, which would support a real EGR-control problem instead of only bad feedback.
Driving risk

Can you keep driving?

P0406 may leave the vehicle driveable, but if the engine surges, idles poorly, or drops into a protective mode, further driving should be limited until the EGR feedback fault is corrected.

Moderate urgency: This code often allows short-term driving, but the right fix usually comes faster when you diagnose it early instead of waiting for more codes.
Likely causes

Common causes behind this code

  • EGR position sensor internally biased high
  • Signal circuit shorted to voltage or crossed with another circuit
  • Ground problem or reference issue distorting the feedback signal upward
  • Connector contamination or pin damage causing irrational feedback
  • Valve-position reporting mismatch inside the electronic EGR assembly

Cause phrases often tied to this code: high EGR position signal, short to voltage, biased EGR sensor, reference problem, connector fault.

Diagnostic order

Suggested workflow

  1. Capture freeze-frame and compare the reported EGR position with commanded position.
  2. Verify reference voltage, ground integrity, and signal voltage at the connector.
  3. Inspect for shorts to voltage, connector damage, or moisture intrusion.
  4. Actuate the valve if possible and watch whether the feedback changes rationally through its range.
  5. After repair, confirm the voltage returns to normal and no related range/performance code remains.
Avoid guesswork

Common mistakes

  • Replacing unrelated drivability parts because the engine surges, when the real clue is the irrational EGR feedback signal.
  • Assuming P0406 is just the opposite of P0405 without testing the circuit for an actual short to voltage.
  • Stopping after the code clears without verifying live feedback is now believable.
Repair path

Practical fix guidance

  • Repair short-to-voltage, ground, or connector faults first if the signal proves electrically impossible.
  • Replace the EGR sensor or valve assembly when the circuit is solid but the feedback remains biased high.
  • Retest under idle and light-cruise conditions so the EGR strategy is stable where it matters most.
Vehicle context

Affected brands in this MVP

Brand hubs help broaden internal linking now and can evolve into make-specific diagnostic notes later.

Aliases and common searches

English phrases tied to P0406

Useful when the driver knows the wording but not the exact DTC yet.

  • EGR sensor high
  • EGR position sensor high voltage
  • EGR feedback circuit high
Related search intent

Queries this page can answer naturally

  • P0406 code meaning
  • what does P0406 mean
  • EGR sensor A circuit high symptoms
  • EGR position high voltage
FAQ

Quick questions about P0406

What is the main difference between P0405 and P0406?

P0405 points to an EGR feedback signal that is too low, while P0406 points to one that is too high.

Can P0406 be caused by wiring?

Yes. A short to voltage, poor ground, or connector problem can all push the signal high.

Should I replace the EGR valve immediately for P0406?

Only after checking the reference, ground, signal wire, and live feedback behavior. Many high-signal faults come from the circuit rather than the valve alone.