I Have a 1996 Lexus Es300 With Error Code P0401 …disconnecting the battery neg terminal did not re-set the error code …replacing the EGR valve…no luck…replaced EGR temp sensor, no luck…next I guess i’ll try replacing vaccum lines…any other ideas??
The code indicates insufficient flow thru the EGR system. The thing you see sitting next to the EGR valve is the EGR valve vacuum control modulator. This determines how much the EGR valve opens and closes. That could be causing the problem.
But might I suggest that you either get an accurate printed manual or an online subscription to like ALLDATA for your vehicle? Because the money that you spent for parts the vehicle didn’t need could have paid for either one of these.
Exhaust Gas Recycle routes some exhaust gas back into the intake manifold when the engine is warm and running at speed. Paradoxically, that causes the engine to run a little cooler and generate fewer Nitrogen Oxides. Here’s a link to a discussion of P0401 that addresses diagnosing your problem http://extreme-check-engine-light-codes.com/blog/obd2/p0401-obd2-fault-code/
On 1970s and 1980s cars with EGR, the engine passages in back of the EGR valve sometimes plugged up with carbon and had to be cleaned out manually. Maybe that’s not a problem any more because the article doesn’t mention it. But I’m quite sure that I had to clean them out on our 1984 Fairlane and I assume that with an OBD2 car (1996 or later), the car would throw P0401 if that condition occurred.
They still do have to be cleaned out. The EGR is not a “part” (the valve) - its a “system” (valve, solenoid, sensor, exhaust feed, intake inlet). You need to check the entire system. Try this for an orientation: http://www.engine-light-help.com/egr-valve.html
- though as Tester noted an actual repair manual for that car will be most helpful.
I had a 1996 Toyota Tercel with the same issue.
The failure ended up being a clogged passage going into the intake manifold from the EGR valve. Try applying vacuum directly to the EGR valve using your mouth on the tube leading to the valve while the engine is idling. If the passage is clear, the engine should stall or idle poorly. Feel underneath the diaphragm with your fingers while applying vacuum, you should be able to feel the diaphragm lift.
If the engine speed doesn’t change, then it is likely that the passage into the intake manifold is blocked with carbon buildup.
I agree whith orange except when you do this try to hold vacuum to see if the diaphragm doesn’t have a leak in it. I agree also with the other posters that there are several parts to this system that can be at fault. It could also be more then one of these sensors or valves that can cause the problem.