OBD-II trouble code
P0406: Exhaust Gas Recirculation Sensor 'A' Circuit High
The EGR position-feedback signal is reading too high — pinned near the top of its range. This is the high-side mirror of P0405: the valve may be moving correctly, but the 'A' sensor reporting its position has gone open or shorted high, so the PCM no longer trusts the feedback.
Quick facts
- System
- Powertrain
- Category
- Emissions / Other
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $50 – $1,200
- DIY difficulty
- Intermediate DIY
Browse every code in P0400–P0499, or start from the full code library.
What does P0406 mean?
P0406 is the high-input member of the EGR 'Sensor A' pair, and it's the direct counterpart to P0405. Both codes are about the position-feedback side of the EGR valve, not the valve's ability to move. Modern electric EGR valves carry a position sensor — usually a potentiometer-style element — that tells the PCM exactly how far the valve has opened. P0405 sets when that feedback voltage drops below the minimum; P0406 sets when it climbs above the maximum the PCM expects. The valve itself can be doing its job perfectly while the sensor circuit reports an impossible position.
The direction of the fault narrows the diagnosis. A high-pinned feedback signal usually means an open circuit — a broken signal-return wire, a corroded connector that's lost continuity, or a sensor element that has failed open. It can also mean the signal wire has shorted to the 5V reference or to another high-voltage circuit nearby. That's the same family of causes as a typical 'circuit high' sensor code: look for a break or a short-to-high rather than a short-to-ground.
It's worth understanding that 'EGR Sensor A/B' means different things across manufacturers. On most gasoline platforms, Sensor A is the valve's integrated position potentiometer, which is why this page's primary repair points at the EGR valve. On some systems the EGR feedback is split across a position channel and a separate temperature/feedback element, which is why a dedicated EGR temperature sensor repair is also offered — on those platforms the 'sensor' that needs replacing may be a standalone part rather than the valve. Identifying which architecture your engine uses is the key first step before buying anything.
Like the rest of the EGR feedback family, P0406 rarely causes dramatic drivability problems because most PCMs default the EGR closed when they lose trustworthy position data. The practical costs are a small fuel-economy hit, an emissions-test failure anywhere an OBD-based inspection runs (the lit lamp alone fails those programs), and — on platforms where EGR ties into intake throttle control — occasional light-throttle hesitation.
Common causes
- Open signal-return wire from the EGR position sensor to the PCM
- Corroded EGR valve connector that has lost continuity on the feedback pin
- Position sensor failed open internally (not separately serviceable on most valves)
- Signal wire shorted to the 5V reference or another high-voltage circuit
- Pushed-back or broken terminal in the EGR connector
- On split-feedback platforms, a failed standalone EGR temperature/feedback sensor
- EGR valve connector left unseated after recent service
- Aftermarket EGR valve producing a feedback range outside spec
Symptoms
- Check engine light on with P0406 stored
- Mild reduction in fuel economy
- Engine often runs normally — most PCMs default the EGR closed when feedback is lost
- Light-throttle hesitation on some platforms
- Failed emissions inspection
- On platforms where EGR ties to intake throttle, possible secondary throttle behavior
Diagnostic steps
- 1.Confirm the EGR valve connector is fully seated and inspect the feedback pin for green corrosion, oil contamination, or a pushed-back terminal.
- 2.Pull all codes. P0406 alone is the position-feedback-only case. P0406 with P0405 or the P0403/P0404 circuit codes broadens the picture.
- 3.Do not back-probe the PCM connector to chase this. The 2007 Jeep Commander P0406 chart says probing those terminals damages them. Work at the valve connector.
- 4.Jumper the position-signal pin to the sensor ground at the valve connector, key on, and watch the position voltage. On that chart a reading that falls below 0.5 V means the harness can be pulled down, and the chart replaces the EGR assembly. A reading that stays high is the open: the next steps are an open signal wire, then an open sensor ground. The chart's cause list for this high code is a signal shorted to the 5 V supply, a signal shorted to battery, either of those opens, the EGR assembly, or the PCM. An open ground is on that list; it does not pull the signal low.
- 5.On split-feedback platforms, determine whether the 'A' sensor is the valve potentiometer or a standalone temperature/feedback sensor before deciding what to replace.
- 6.If wiring tests clean and the valve carries the sensor, replace the EGR valve. Command it through its range afterward and confirm feedback tracks correctly.
Repair cost
$50 – $1,200
Plugging the connector back in is the small job. A pigtail or harness repair is next, and access decides how far that goes. When the position sensor is built into the valve and the harness has tested clean, the valve itself is the large job. On a split-feedback system a standalone temperature or feedback sensor is the smaller parts path. Integrated throttle-and-EGR units on some European engines can exceed the top of this span. Connector and wiring checks come before condemning the valve. Call the printed bracket a planning span, not a firm price. Figure parts and the labor time in this vehicle's service information.
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DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.