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Severity: Low Code type: Generic (all makes)

P0406 Code: Exhaust Gas Recirculation Sensor A Circuit High

The EGR feedback sensor is reporting close to 5 volts or more, above anything a working sensor would send.

At a glance

Severity: 2/5 – Low2/5

Severity: Low

Meaning
Exhaust Gas Recirculation Sensor A Circuit High
System
Emission Controls · Powertrain
Safe to drive?
Yes, short term
Typical repair cost
$40–$700
DIY difficulty
Easy

P0406 is the mirror image of P0405: the EGR position or pressure sensor signal has risen above the highest plausible value, usually sitting near the full 5-volt reference or even higher. A sensor output can only climb that far if the sensor has lost its ground, if the signal wire is touching the reference or a 12-volt wire, or if the sensor has failed internally. On electronic EGR valves the motor wires and the sensor wires usually share one connector, so moisture or corrosion bridging those pins is a surprisingly frequent cause. As with the low-voltage code, the ECU usually disables EGR until the signal is plausible again.

Can I keep driving? Safe to drive in the meantime. Expect possible light pinging under load; if the valve motor wiring is shorted into the sensor circuit, fix it soon because it can damage the ECU's reference circuit.

How to read P0406

How to read P0406P10243064
  1. P Powertrain
  2. 0 Generic (SAE)
  3. 4 Auxiliary emission controls
  4. 06 Specific fault

Symptoms

  • Check engine light on
  • Usually normal drivability
  • Scan tool shows EGR position at or near 100% or about 5 V with the engine off
  • Light pinging under load on gasoline engines
  • Code sometimes appears after washing the engine or driving in heavy rain

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Sensor ground open: broken wire, loose pin or corroded ground connection 30%
  2. EGR position or DPFE sensor failed internally and reads high 28%
  3. Corrosion or moisture bridging the signal pin to the reference or motor pin in the connector 20%
  4. Signal wire chafed and shorted to a 12-volt wire in the harness 12%
  5. Wrong replacement valve with a different connector pinout 6%
  6. ECU fault on the reference or signal input 4%

Diagnosis step by step

Diagnostic flow: P04061Confirm the reading with the engineoff2Unplug the sensor and watch the PID3Measure the ground under load4Check the signal wire for 12 volts5Inspect the connector closely6Replace the sensor and verify

  1. Confirm the reading with the engine off

    With the key on and engine off, the EGR sensor PID should sit at its closed baseline. A reading near 5 V or a position of 100% while the valve is obviously shut confirms the high-voltage condition.

    Tools: OBD-II scanner

  2. Unplug the sensor and watch the PID

    Disconnect the sensor with the key on. On most ECUs the signal then drops to near 0 V, which proves the wiring isn't feeding voltage in and points to the sensor or its ground. If the reading stays high with the sensor unplugged, the signal wire is shorted to voltage.

    Tools: OBD-II scanner

  3. Measure the ground under load

    Reconnect the sensor, back-probe its ground pin and measure against battery negative with the key on. More than about 0.1 V here means a poor ground somewhere between the sensor and the ECU.

    Tools: Multimeter

  4. Check the signal wire for 12 volts

    With the sensor unplugged, measure the signal pin to ground with the key on and while the EGR valve is commanded. Any reading well above 5 V means the signal wire is touching a battery or motor feed somewhere in the harness.

    Tools: Multimeter, OBD-II scanner

  5. Inspect the connector closely

    Look for green or white corrosion, water trapped behind the seal and pins that have spread. Clean with contact cleaner, dry thoroughly and replace a connector whose housing is cracked.

    Tools: Flashlight, Screwdriver

  6. Replace the sensor and verify

    If reference, ground and signal wiring all test good, replace the sensor or the valve that contains it. Clear the code and confirm the reading now rests at baseline with the engine off and moves smoothly when EGR is active.

    Tools: OBD-II scanner

Where the parts are

Ignition: coils and spark plugs per cylinder – P04061234567
Ignition: coils and spark plugs per cylinder
  1. 1Ignition coil
  2. 2Spark plug
  3. 3Fuel injector
  4. 4Camshaft sensor
  5. 5Crankshaft sensor
  6. 6Engine computer (ECM)
  7. 7Intake manifold

Repair options & costs

RepairDIY?Estimated cost
Clean, dry and reseal connector Yes $40–$130
Repair sensor ground or shorted wire No $100–$300
Replace DPFE sensor (Ford) Yes $90–$250
Replace EGR valve with integrated sensor No $250–$700

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Notes by brand

Field data

Jeep 2 Grand Cherokee Srt, Wrangler

Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.

Emissions / smog test impact

Will fail

With P0406 stored and the check engine light on, the car fails an OBD-based smog check. Clearing the code without a repair only leaves the EGR monitor not ready.

Frequently asked questions

Why would a sensor read too high?

A three-wire sensor can only output close to its full 5-volt supply if it has lost its ground, if the signal wire is touching voltage, or if it failed internally. That's why the ground and wiring checks come before buying parts.

Could washing the engine have caused P0406?

Yes. Water forced into the EGR connector can bridge the signal pin to the reference or motor pin. Drying and sealing the connector often clears it, but check for corrosion that will keep causing trouble.

Can I clean the sensor to fix it?

Not for this code. P0406 is an electrical fault, so carbon on the valve doesn't cause it; the fix is in the wiring, the connector or the sensor itself.

Sources