P0406 code: Exhaust Gas Recirculation Sensor A Circuit High
P0406 means exhaust Gas Recirculation Sensor A Circuit High. The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0406 means
The EGR position sensor tells the computer how far the EGR valve is open. P0406 means that sensor's signal is reading too high. The usual causes are a failed EGR position sensor, a wiring fault (open or shorted high), or a corroded connector. On many EGR valves the position sensor is built into the valve, so the repair can mean replacing the valve assembly. It's mostly an emissions issue and rarely changes how the car drives.
P0406 symptoms
- Check-engine light, usually with no obvious change
- Occasional rough idle or light pinging under load
- Failed emissions test
What it costs to fix P0406
Typical range: $60–$400 · about ~0.3–1.5 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| EGR position sensor | $25–$100 | ~0.3–1 hrs |
| EGR valve (sensor integrated) | $50–$300 | ~0.5–1.5 hrs |
| Wiring / connector repair | $10–$120 | ~0.5–1.5 hrs |
A standalone position sensor is cheap. The cost rises only if the sensor is built into the EGR valve and the whole valve is replaced. A wiring/connector fix is inexpensive once located.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0406 for my exact vehicle →
How to fix P0406
Moderate — doable at home with common tools and patience
- Read the EGR position value with the valve closed
With the key on and the engine off, check what EGR position the computer reports. A value pinned at the top of its range while the valve is physically shut confirms a high-circuit fault rather than a valve stuck open, and tells you the fault is present right now — which makes it far easier to chase than an intermittent one.
- Check the connector for moisture and pushed-out pins
Unplug the EGR valve or sensor connector and look for water, corrosion bridging the pins, or a terminal that has backed out of the housing. A ground pin that has lost contact lets the signal float up toward reference voltage, which is one of the most common ways this code sets with a perfectly healthy sensor.
- Voltage-drop test the sensor ground
With the key on and everything plugged in, back-probe the sensor ground pin and measure to battery negative. A clean sensor ground typically shows around a tenth of a volt or less; a reading climbing toward several volts means the return path is open or corroded. If other sensors also set high codes, suspect the ground they share.
- Compare the signal to the reference voltage
Back-probe the signal and reference together. A signal equal to the reference at every valve position, with a good ground, means the sensor's internal track has opened. A signal reading higher than the reference — up near battery voltage — means the signal wire is shorted to a 12-volt circuit somewhere in the harness.
- Replace the EGR valve or sensor and clear the code
With power, ground, and signal wiring proven, the sensor itself has failed. Many valves integrate the sensor, so the complete valve is replaced with a fresh gasket; budget valves have a reputation for short lives, so a quality part is worth it here. Clear the code and watch position follow the commanded value on a test drive.
DIY or shop? P0406 is mostly multimeter work: a ground that has lost contact or a pin that has backed out accounts for many cases, and both are fixable in the driveway. Replacing an accessible EGR valve is a moderate wrench job. Hand it to a shop when the signal reads above reference and the short to voltage can't be found with a visual check and a wiggle, since tracing it properly needs a wiring diagram, or when the valve sits under the intake manifold on your engine.
Tools for the DIY steps: Digital multimeter with back-probe pins · OBD-II scan tool with live data · Electrical contact cleaner · Basic socket and wrench set · New EGR valve gasket
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0406.
Start a case with P0406 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0406?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0406: common questions
Can I drive with P0406?
That's beyond what a code alone can tell. P0406 is primarily an emissions code — address any pinging sooner, and plan to fix it before an emissions test.
Is P0406 the sensor or the valve?
Often the EGR position sensor or its wiring. On valves where the sensor is built in, the repair may mean the whole valve assembly. Checking the wiring first can save replacing a part that was fine.
What does 'circuit high' mean for P0406?
The EGR position sensor's voltage is at the high end, which usually means a failed sensor or a wire shorted high rather than a real valve position. Diagnosis confirms which.
How much does it cost to fix P0406?
Inexpensive if it's a standalone sensor or wiring; more if the sensor is integrated into the EGR valve and the valve is replaced. Check the connector before buying parts.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0406 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0406 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.