What Does P0406 Mean?
The EGR (Exhaust Gas Recirculation) position sensor A is reporting a voltage above the expected maximum threshold. The ECM sees the sensor signal voltage stuck high, indicating either a short to voltage, an open ground circuit, or a failed sensor. The driver may experience rough idle if the ECM interprets this as the EGR valve being stuck open, or the system may simply disable EGR and set the MIL.
Common Causes
30%
Failed EGR position sensor outputting continuously high voltage
25%
Signal wire shorted to the 5V reference or battery voltage
20%
Open ground circuit at the EGR position sensor
15%
Corroded connector with high resistance on the ground circuit
10%
ECM input circuit fault reading the signal high
Diagnostic Steps
1
With key on engine off, check the EGR position sensor voltage PID — it should read approximately 0.4–0.9V with the valve closed. A reading near or above 4.5V confirms a high circuit condition.
2
Disconnect the sensor connector and check the signal pin at the ECM — if voltage drops to near 0V, the sensor is failed. If it remains high, the wire is shorted to a voltage source.
3
Verify the ground circuit by measuring resistance from the sensor connector ground pin to ECM ground pin — should be under 5 ohms. Infinite resistance indicates an open ground.
4
Inspect the connector for corrosion, bent pins, or physical damage. Look for wiring that may have chafed against a voltage source.
5
If all circuits test good, swap with a known-good EGR sensor (if separable) or replace the EGR valve assembly.
Estimated Repair Cost
$80 - $350
Parts + labor, varies by vehicle and location
The EGR (Exhaust Gas Recirculation) position sensor A is reporting a voltage above the expected maximum threshold. The ECM sees the sensor signal voltage stuck high, indicating either a short to voltage, an open ground circuit, or a failed sensor. The driver may experience rough idle if the ECM inte...
The most common cause of P0406 (Exhaust Gas Recirculation Sensor A Circuit High) is: Failed EGR position sensor outputting continuously high voltage
Typical repair costs for P0406 range from $80 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive. The ECM will disable EGR control, which primarily affects emissions. If the ECM misinterprets the high signal as the valve being open, it may try to compensate fuel mixture, causing rough idle. Will fail emissions testing.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0406 to identify the root cause.
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Quick Info
Category
Powertrain
System
Emissions Control / EGR System
Difficulty
Type
Generic (SAE)
Recommended Tools
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