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Q: Check Engine Light is on - code P0405

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In the last year and a half my husband has changed the EGR valve twice, cleaned out the ports and also the fuel pressure regulator, but the check engine light comes back on after just a few miles. The code is p0405 - what else could be causing the light to come on?

My car has 129050 miles.
My car has an automatic transmission.

This code could be caused by the EGR valve, the EGR valve position sensor, a wiring or connector issue, or even a problem with the PCM. P0405 is set when the PCM sees a voltage reading below .35 volts. So, there are actually several issues that can cause this reading to be low.

There is a long diagnostic flow chart to diagnose this particular trouble code. It would be best to consult a certified mechanic, such as one from YourMechanic, who will have access to the tools and flow chart needed to diagnose why the Check Engine Light is on and what is giving rise to code P0405.

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