P0405 indicates that the engine control module has detected a voltage signal from the exhaust gas recirculation (EGR) position sensor that is lower than the expected range. This typically means the sensor circuit is open, shorted to ground, or the sensor itself is not providing a proper signal.
The sensor internal element may be damaged or worn, causing it to output a voltage below the minimum threshold.
Broken wires, corroded terminals, or a loose connector can prevent the sensor signal from reaching the ECM.
Insulation damage or a pinched harness can pull the sensor voltage low, triggering the code.
A valve that cannot move to the commanded position may cause the position sensor to report an abnormally low voltage.
Insufficient vacuum or a faulty solenoid can keep the EGR valve in a position that the sensor reads as low.
A defective driver circuit inside the control module could misread a normal sensor voltage as low, but this is uncommon.
No. The ECM is rarely the cause; most P0405 faults are due to the sensor, wiring, or EGR valve. Replacing the ECM without confirming a driver fault usually does not fix the problem.
The vehicle will run, but you may experience reduced performance, higher emissions, and possible stalling. It is advisable to diagnose and repair promptly.
Clearing the code only resets the check engine light. If the underlying fault remains, the code will return after the ECM re‑evaluates the sensor circuit.
A vacuum leak that affects the EGR system can keep the valve in a position that the sensor reads as low, indirectly triggering the code.