Code PO401

[vegascraps91]

Hello,

I have a 95 Previa S/C 186K. The check engine light came on code reads PO401 bad EGR. I found a factory EGR online for $149. The engine sputters when getting on the gas or driving up hill when using regular unleaded. But it runs perfect when using premium unleaded. My van has already passed emissions. So my question is will it harm the engine if I do not replace the EGR and continue to use premium fuel? I had a 93 MR2 non turbo reading the same code and drove it for a year with no issues. Thank you in advance for any advice you can give me.

[timsrv]

EGR is an emission required device. When EGR is activated it allows Exhaust Gas to Recirculate back through the intake manifold. This actually makes the engine run worse but helps reduce emissions. When the system is functioning correctly the EGR is limited to only operate when the engine is hot & RPMs are up (so it won't cause rough running or drivability issues). Due to your hesitation issue I'm guessing the EGR is not turning off, but staying on at all times. Driving a vehicle with a malfunctioning EGR shouldn't hurt anything. If it doesn't function at all the engine will actually run better, but will have slightly higher emissions. This in itself may not cause it to fail emission testing but coupled with other faults may lead to a failed emission test. Driving with a constantly activated EGR shouldn't hurt anything either, and probably won't effect emission testing. You may however experience rough running and/or hesitation when idling or initiating acceleration. As for a cure? It's probably not the EGR valve itself, but more likely a malfuncion of the system that limits it's operation. Tim

[vegascraps91]

Tim,

Thank you for getting back to me so quickly. I appreciate your input. I did not want to start throwing parts at something that is not a crucial issue. For now I will use only premium fuel and just ignore the check engine light since the EGR is the only code popping up right now and scan it periodically to make sure there are no other issues. Thanks again for your help.

[vegascraps91]

UPDATE...... The sputtering problem with my bean was getting a lot worse. So last weekend I decided to pull it in the driveway and try to fix it. I ordered a EGR valve and cool air intake duct gasket from

Toyota. I removed the EGR cleaned it and tested it seem to be working fine. I then removed the cool air intake duct to find that the EGR port was clogged full of carbon just like Tim said it was a malfunction

in the system before getting to the EGR. I inspected the air hose intake for cracks and found none. I cleaned the throttle body and MAF and took it for a test drive. CEL is off now but still sputtered on

acceleration. Went to Costless and got NGK plugs, wires, cap, rotor and a aftermarket fuel filter. While performing the tune up I found that the previous owner had all Carquest aftermarket parts

installed. Took it for a test drive and the hesitation is now gone Don't know what exactly was causing the issue after replacing so many different parts just happy the sputtering is finally gone. I took the Previa for a road trip to Medford, OR the following weekend and it climbed through the pass like a champ

[timsrv]

Awesome! Sounds like my 92 Previa. I got it for a great price because it ran bad. Other than the fact it had aftermarket plug wires everything looked good. I replaced all the tune-up parts & filters with genuine Toyota parts and it purred like a kitten from that day forward.............until a drunk driver hit me and totaled it about 4 years later. .

[TheMAN]

there's a lot of misconceptions and misinformation about EGR valves out there
they do NOT make the engine "run worse"! the only time they do that is when they malfunction, and you get poor acceleration/lack of power, or rough idle

under normal conditions, the EGR valve is only activated under steady cruise, high vacuum... the EGR system is designed to reduce NOx emissions, but it also has a secondary effect of decreasing engine pumping loss, which therefore has the potential of increasing gas mileage

poor fuels, and/or lack of tune up, causes a richer/sootier exhaust... that contributes to EGR pipes or valves clogging

[Jonny]

If you're having recurring EGR codes after replacing components check for air flow through the steel spider pipes which connect the modulator with the other parts of the system. Two of those pipes were blocked with rust on my Previa.