Read more: Code P0401.Īnother problem with an EGR valve is when it gets burned through or 'explodes'. In some older Ford vehicles, some EGR codes were caused by a bad DPFE sensor. Clogged EGR passages can cause problems similar to a bad EGR valve. Not all EGR problems are caused by a failed EGR valve. The EGR valve must be replaced to repair the problem. In many Mazda/Ford 4-cylinder engines, the code P0401 can be caused by a sticking EGR valve. Steps to diagnoseĬarbon buildup causes an EGR valve to stickĮGR valve failures causing the code P0401 were common in the Mazda CX-7 vehicles with a 2.3L turbo engine.

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