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2004 Mitsubishi Lancer Ralliart P0401 Code: Causes, Diagnosis & Safe Fixes

Model: 2004 Mitsubishi Lancer Ralliart Fault Code: P0401 Posted: 2008-10-23 13:09

My check engine light came on recently, and after connecting a diagnostic tool, I received the OBD-II code P0401. I've researched what this code means and found several potential causes: Causes of P0401: - A faulty DPFE (Differential Pressure Feedback EGR) sensor - Blockage in the EGR tube, typically due to carbon buildup - A malfunctioning EGR valve - The EGR valve failing to open due to insufficient vacuum Possible Solutions: - Replacing the EGR valve alone often doesn't resolve the issue, as it's not always the root cause. - Use a vacuum pump to manually activate the EGR valve while monitoring engine RPM and DPFE sensor voltage. A noticeable change in RPM should occur when the valve is open. - Clean the EGR valve and/or its tubing to remove deposits. - Check the DPFE sensor voltage against manufacturer specifications (refer to your vehicle's repair manual). - Replace the DPFE sensor with a high-quality or OEM unit. - Replace the EGR valve if necessary. I'm new to this car—my 2004 Mitsubishi Lancer Ralliart was purchased about three months ago. Before that, I drove it from Edmonton, AB to Vancouver, BC and back last month. During that trip, I switched to synthetic oil and higher-octane fuel (premium 92 octane). Could this have contributed to the P0401 code? I don't know where the EGR valve is located or how to safely access it. Can anyone provide clear guidance on diagnosing and fixing this issue without causing further damage? I want a safe, reliable solution that avoids unnecessary part replacements.

Related fault codes
P0401
Comments (3)
Anonymous 2008-10-24 12:47

This is unlikely to be the cause. I recently had a similar EGR code on my Mitsubishi Lancer, and my parts supplier’s daughter has one too. When they contacted Mitsubishi Parts, they stated that EGR valve failure isn't common in this model—so it's worth checking other possibilities first.

Anonymous 2008-10-25 13:10

The most frequent cause of P0401 is a clogged EGR passage. To test this: apply vacuum to the EGR valve while the engine is running. If the engine stalls or runs very roughly, it indicates blockage in the passages. Also, check the small vacuum lines near the throttle body that feed into the EGR control solenoid—ensure they aren't blocked. These hoses typically don’t produce vacuum until engine RPM increases.

Anonymous 2009-06-25 21:51

I know this post is a bit old, but I wanted to share: I had exactly the same P0401 code on my Mitsubishi Evo. It turned out to be a disconnected vacuum hose from the EGR valve. I reattached it with a zip tie and reset the ECU—since then, the issue has not returned. This is something worth checking as well.