P0406
Exhaust Gas Recirculation Sensor "A" Circuit High
Moderateegr
Overview
The P0406 code indicates the PCM has detected a exhaust gas recirculation sensor "a" circuit high fault in the exhaust gas recirculation (EGR) system. The EGR system reduces nitrogen oxide (NOx) emissions by recirculating a controlled amount of exhaust gas back into the intake manifold. An EGR malfunction can cause rough running, engine knocking, and increased emissions.
Symptoms
- Engine knocking or pinging
- Reduced fuel economy
- Rough idle
- Check Engine Light (MIL) illuminated
Common Causes
- Failed EGR valve (stuck open or closed)
- Faulty PCM commanding incorrect EGR operation
- Clogged EGR passages or tubes
- Wiring issues in EGR circuit
Diagnosis Steps
- 1Connect an OBD-II scanner and read all stored trouble codes and freeze frame data
- 2Inspect the EGR valve for carbon buildup; clean or replace as needed
- 3Test the EGR valve operation by applying vacuum or using the scan tool
- 4Check EGR passages for carbon blockage
- 5Test the EGR position sensor and wiring with a multimeter
Estimated Repair Cost
$150 — $600
Cost varies by vehicle, location, and repair shop. Includes parts and labor.
Commonly Affected Vehicles
Nissan FrontierHonda CR-VRam 1500Ford F-150
Related Codes
More Egr Codes
P0400Exhaust Gas Recirculation Flow Malfunction
ModerateP0401Exhaust Gas Recirculation Flow Insufficient Detected
ModerateP0402Exhaust Gas Recirculation Flow Excessive Detected
ModerateP0403Exhaust Gas Recirculation Circuit Malfunction
ModerateP0404Exhaust Gas Recirculation Circuit Range/Performance
ModerateP0405Exhaust Gas Recirculation Sensor "A" Circuit Low
ModerateFrequently Asked Questions
Yes, EGR valves clogged with carbon can often be cleaned using throttle body or EGR cleaner. This is a cost-effective first step before considering replacement.