I HAVE BEEN TRYING SINCE JULY TO FIND OUT WHY MY SERVICE ENGINE LIGHT CONTINUES TO KEEP COMING ON.THE CODE IS PO401,WHICH IS INSUFFICIENT AIR FLOW. I HAVE TAKEN MY CAR TO MITSUBISHI AND PRECISION AUTO; BETWEEN THE TWO I HAVE REPLACED THE EGR SOLENOID AND VALVE, THE MAPS SENSOR, THE MASS AIR FLOW SENSOR, THE O2 SENSORS,REPLACED HOSES AND CLEANED THE TUBING FOR CARBON BUILDUP. NOW PRECISION THINKS IT MIGHT BE THE COMPUTER SYSTEM IN THE CAR. IF SO HOW WILL YOU KNOW WITHOUT HAVING TO REPLACE THE COMPUTER? IS THERE A TEST?. ALL I KNOW THE SERVICE ENGINE LIGHT CONTINUES TO COME BACK ON. PLEASE HELP!!!! ANY SUGGESTIONS!!!!
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2001 Mitsubishi Eclipse Question: SERVICE ENGINE LIGHT/CODE PO401
Answer #1MATCO57 January 04, 2012, 21:06Enthusiast
You need to start over and look for another shop.
Tests/Procedures: 1. Try blowing through the EGR solenoid with it disconnected, it should flow freely.
2. If it is restricted, replace the solenoid.
3. If not, check the vacuum hose from the solenoid to the throttle body for a restriction.
Answer #2patrick mannion from Greg Solow's Engine Room, January 04, 2012, 22:14Master
I hate seeing parts replaced without a problem being found and cures. An EGR control circuit can be tested by taping into the EGR hose at the valve and taping a vacuum gauge to the windscreen and then driving the car. If the EGR doesn't get vacuum when it should the circuit needs to be tested. I have seen the Eclipse computers fail, there are several companies that specialize in the testing and repair of the ECU computer. Fuel Injection Corporation in Livermore California are very god quick turn around time to test and or test and repair your computer.