The code comes back to "on" after the work is done and about 50 miles are driven. I have done many things to solve this and am perplexed.
P0401 is a code that many post about, but nothing has fixed this nagging code. The vehicle shows no symptoms, and drives well.
Please assist.
1999 RAV4 AWD Manual transmission
1) VSV is new. 12 Volt Excitation is good. The valve shuts off and works properly. VSV is rerouted to the top of the engine compartment in an improved place for access.
A) With power off, flow exists between the ports.
B) With power on, 90 degree port flows into the filter. There is no flow between the ports.
2) EGR is new. If a vacuum is pulled from a source connected to the EGR you can stall the car. This is a dynamic working test.
3) Modulator is new. Throttle the engine up and it pulls vacuum.
4) PCV valve is new and replaced.
5) Tubing is new. There are no suspect existing tubes that seem compromised.
6) Today I took the EGR off again and inserted a coat hanger into the tube, it was clear of occlusion.
7) Last attempt is to order a Vapor Pressure Sensor. It can be installed easily and returned if it is not a fix.
Q1_ Are there inherent underlying codes that need to be reset over and above a disconnect from the battery terminals to do a hard reset? I would like to know if there can be more codes attached to the basic P0401 that must be reset by a device.
Thank you for the detailed link. The problem is that everything on that list is covered, I have replaced all of the parts, Tested them, and the code still exists when reset by disconnect of the battery terminal. There is something else that has not been exposed.
