6G Celicas Forums

Today is my last day of legal driving. We found the new vsv I bought was faulty, so I bought another one, we tested it, it works. Check engine light came back on last night, still egr. Replaced all the necessary parts, egr, modulator and vsv, new vacuum lines, everything is clean. We are truly at a loss. Maybe 02 sensor? I read about it. P0401. Never ending. This sucks.

Did you replace it with an OEM one? There is a known issue with aftermarket EGR VSV's on 5SFE, and many folks have had issue with aftermarket valves.
Also make sure you re-connect the vacuum lines correctly after the installation of the new valves. It's easy to switch them around. I learned that the hard way

This post has been edited by slavie: Mar 2, 2018 - 12:44 PM

I have been fighting this same code for almost a year.

What have you replaced? I'm trying 02 sensor next. Then evap canister. Do you have any information? Maybe we can help each other.

have you checked the wiring from the ECU to the VSV? maybe its not being triggered

I know know how to get to the ecu, but which wires, I was just thinking about checking that yesterday

That P0401 code is a bitch. I've had to deal with it for almost 4 years. I replaced almost everything besides the Evap canister, I need a new EGR VSV because the aftermarket EGR VSV is bought was faulty too, I will replace with OEM soon. I'm convinced its the charcoal canister that is the main culprit. On another thread a user fixed his P0401 by replacing the canister with a used one from a salvage yard.

How would a component from the evap system affect the egr system? That would be like a stuck seat slider causing an engine misfire.

My friend and I got a canister from a yard, but we haven't put it on yet cause it looks different, there's more vacuum lines. The hood was missing from the car so I don't know if it was federal emissions, but the canister was in the same spot, so I'm not sure if it would work. Probably have to buy a new one, and that's almost 400. Oops, this reply was for micronian.

This post has been edited by ST204GT83: Mar 11, 2018 - 9:46 AM

Bitter, are there supposed to be holes for vacuum from the egr, to the throttle body, through the throttle body and gasket into the intake manifold?

the charcoal canister has NOTHING to do with the EGR.

what year is the car, i might have the wiring diagram

Have you actually tested the EGR system? The factory service manual provides very, very detailed steps on how to test every component of the system. Throwing parts at the problem, while easy, is not the best solution, as new parts can be defective as well, especially if you're getting aftermarket stuff.

To set the P0401 or 0402 codes, the computer actually goes by the MAP sensor data. Basically, when EGR is opened or closed, the computer is programmed to look for a specific change in the engine vacuum, all else being equal. If there is no change in the vaccum reading, you'll get P0401 (malfunctioning EGR VSV, modulator, or valve); alternatively, if the change in vacuum is too great, you get P0402. There is literally no other way for the computer to determine whether the EGR system is working (I'm not sure if the ECU measures the draw on the VSV pin, so that could be another code setting criteria).

If you actually hook up a vacuum gauge to the system and follow the diagnostic steps, you should be able to see exactly the condition that set the code. Also, look at the freeze frame data.

I too fail to see how EVAP system component - the canister - will solve your EGR system code. Theoretically if there was a break in the EVAP system that was leaking too much vacuum you might see an impact on the EGR system, but then you would be seeing EVAP system codes as that has the vapor pressure sensor and is a much easier system for the ECU to monitor and throw codes for.

1999 GT federal emissions

Possible causes for P0401:
EGR passage clogged (had this before, pull egr valve and clean built-up carbon from valve, tubing and passages in intake.)
Faulty EGR Vacuum Modulator Valve
Faulty EGR Valve
Faulty EGR solenoid valve
EGR solenoid valve harness is open or shorted
EGR solenoid valve circuit poor electrical connection
Dead (Weak) battery
Faulty EGR temperature sensor and circuit
Exhaust gas leaks

Read more: https://www.engine-codes.com/p0401_toyota.html

This post has been edited by 97GTinKC: Mar 20, 2018 - 1:53 PM

Had that issue on a '99 camry we owned. I put on a cold air intake on it and it tossed up an EGR code after that. Fixed just about everything EGR related on that car and the light never went away. My brother eventually totaled out the car and that was the solution to our EGR problem.

That's what I keep hearing, the light doesn't go away lol. I need to get another 94 ST.

I'm gonna repeat my own question one more time. Again, the EGR vacuum switching valve, as is the case with other VSV's, draws a metered amount of vacuum, and this vacuum draw is what ECU detects through MAP sensor to throw codes (as I explained in my 2nd post here, which was also ignored). Which one did you put in? OEM, or aftermarket garbage?

First one was aftermarket, second one I got at autozone for $70, the guys at the shop also put on another one on with no result. Three have been used.

MAKE SURE the vacuum lines are connected correctly to the EGR VSV. They are VERY easy to switch, and you will 100% guaranteed get a CEL if you do.

Here's the OEM VSV - $77:
https://parts.toyotaofcoolsprings.com/oem-p...alve-2586074050
The $70 from AZ is same crap as any other aftermarket ones, and likely what the shop tried.

Here is a fantastic video of Toyota ERG system diagnosis (from a Corolla, same operation and diagnosis):
https://www.youtube.com/watch?v=WOSFmKY15SU
It also answers your question about why the 2 vac ports on the throttle body are blocked by the gasket - they only open when throttle is open, not all the time.

For ECU wiring, it's pin #23 on the 26-pin (largest) connector. Here's a wiring FSM from a Camry, look at page 90 (same pinout, though wire color I think is different):
http://www.josvandijken.nl/downloads/pdf/b...oyota_camry.pdf

If you do all of the above and everything checks out (with OEM vsv), then replace ECU (with identical P/N). Electronic components within the ECU "dry up" and can start acting up. There have been cases where ECU replacement solved the P0401 code, here:
http://www.toyotanation.com/forum/103-camr...ml#post12813250

Thank you for all your information sir, I really appreciate it!