Hi everyone, im new to the Evo community and i purchased a 2003 Evo a few weeks ago. So last week i got a CEL code p0401. I cleaned the EGR valve and replaced the gasket for that valve. I cleared the code and after 130 miles of driving the same code popped up again. Now im not sure if i need to get new hoses for the EGR system, get a new EGR solenoid or take the L and spend $250-300 on a new EGR valve. Need help.

 

Just started looking for the same thing myself today. This thread has another possible cause: https://www.evolutionm.net/forums/ev...ry-solved.html. Just getting started on mine so I haven't done anything yet beyond checking the code...

 

I'd say delete it but you're in Commiefornia. Get a tune and delete the emissions codes from the ecu is an option.

 

If the EGR monitor is not setting in the drive cycle, you will get a P0401.

For the EGR readiness test to complete, there are a few things that must happen together. First the EGR valve must open when commanded by the ECU. This requires a leak free vacuum line between inlet manifold and EGR solenoid, a solenoid that opens when energized, and a leak free vac line from solenoid to EGR valve. I'm going to assume that your EGR valve's diaphragm is not punctured (test it if not sure). This part of the troubleshooting is where most of the problems are found. It is usually mis-connected vac lines, a failed solenoid or broken wiring. Check them and report back.

Once you have checked routing of the vac lines, tested the solenoid and wiring, make sure the EGR valve is actually opening. Use a hand vacuum pump to suck on on the line to the EGR, and listen for the idle to roughen up as exhaust gasses get sucked into the manifold. If the idle doesn't roughen up when you suck on the valve, pull it off the manifold and check the passages in the manifold aren't blocked up with carbon. I've had to clean mine out a couple of times. Next, once you have got the EGR injecting gasses, the MAP sensor on the top of the inlet manifold must register a tiny vacuum drop when the EGR valve opens. Check your MAP sensor is OK. The ECU runs the EGR test once the engine is fully warmed up, so it also requires a working coolant temperature sensor. Check your temp sensor (screws in to the thermostat housing on the right end of the block) is working and accurate. The EGR test also depends on an accurate throttle position sensor (TPS) to tell it when you are opening the throttle, and on your crankshaft position sensor (CPS) to read RPM. Check them both.

Here are some details from the FSM:

DTC P0401: EXHAUST GAS RECIRCULATION FLOW INSUFFICIENT DETECTED
.
TECHNICAL DESCRIPTION
• When the EGR vacuum regulator solenoid valve switches from "OFF" to "ON" while the engine is running, EGR gas flows.
• The ECM checks how the EGR gas flow signal changes.
.
DTC SET CONDITIONS
Check Conditions
• At least 20 seconds have passed since the last monitor was complete.
• Engine coolant temperature is higher than 76°C (169°F).
• Engine speed is at between 1,000 and 2,000 r/min.
• Intake air temperature is higher than 0°C (32°F).
• Barometric pressure is higher than 76 kPa (11 psi).
• Vehicle speed is 1.5 km/h (0.9 mph) or more.
• At least 90 seconds have passed since manifold differential pressure sensor output voltage fluctuated 1.5 volts or more.
• The throttle valve is closed.
• Volumetric efficiency is lower than 20 percent.
• While fuel is being shut off.
• The ECM monitors for this condition for 3 cycles of 2 seconds each during the drive cycle.

Judgement Criteria
• The intake manifold pressure fluctuation width is lower than 3.5 kPa (0.50 psi). When the EGR
vacuum regulator solenoid valve is turned ON.
.
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are: )
• EGR valve does not open.
• EGR control vacuum is too low.
• EGR vacuum regulator solenoid valve failed.
• Open or shorted EGR vacuum regulator solenoid valve circuit, or loose connector.
• Manifold differential pressure sensor failed.
• ECM failed.
__________________

 

Thanks for sharing! Im for sure gonna check my MAP sensor o ring tonight after work.

 

Yea, if i was in a state that wasn't so strict on emissions i'd delete it.

 

Hello, can you please comment the solution? What happend? how Do you solve this problem? i'm having the same issue with my Lancer ES 05.

 

I recently got my Evo 9 tuned, after 20 or so miles my service engine light came out and it was a P0401 code.

I pressure checked the EGR valve and it was good to go. Double checked all of the lines, good to go. I decided to change my EGR solenoid. Got the new solenoid in, went for a drive and sadly the P0401 came back.

I decided to go back to my stock tune on a hunch, since everything was normal before my flash tune. 100 miles in and no service engine light for P0401. I reached out to my tuner to see if he could double check my tune file and see if there was something wrong. I am hoping it's a simple fix. The tune made the car feel great.

Anyone have any other potential advice?