P0406 - Exhaust Gas Recirculation Sensor 'A' Circuit High
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
Diagnostic Trouble Code (DTC) P0406 is set when the Engine Control Unit (ECU) detects that the Exhaust Gas Recirculation (EGR) sensor 'A' (typically the pintle position sensor) is reporting a voltage signal that is higher than the maximum calibrated limit. Generally, this means the signal exceeds 4.5–4.8 Volts. The EGR system reduces combustion temperatures to decrease Nitrogen Oxides (NOx) emissions. A high circuit code typically points toward a loss of ground, a short to voltage on the signal wire, or an internal sensor failure.
Possible Causes
Faulty EGR valve (internal short in the position sensor)
Open circuit in the sensor ground wire
Short to 5V reference voltage on the signal wire
Faulty Engine Control Unit (ECU)
Symptoms
Recommended Solution
Workflow
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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