Toyota Nation Forum banner

1 - 20 of 40 Posts

·
Registered
Joined
·
21 Posts
Discussion Starter #1 (Edited)
Hello. I own a 96 Paseo (manual 5eFe) which has had a P0401 code for quite some time now. I have no drivability issues. I've tried multiple things to try to clear it, including cleaning the ports, checking for vacuum leaks, tested the components with a hand pump. Reset the code after I change something only to have it come back on after the second full "key cycle". Engine dies when I apply enough vacuum to egr valve. Map sensor is receiving 5 volt reference and 3.5 volts on signal wire with no vacuum applied (goes down with vacuum applied). VSV functions when manually energized (tested disconnected from the ECU of coarse). And although I wouldn't normally do this, I bought a new Egr valve, vacuum modulator, and VSV out of a sort of desperation to make sure I didn't miss anything. I even used Sea Foam Spray through the engine to make sure I didn't miss any carbon buildup as well as buying a new PCV valve (as I've heard those may sometimes trigger a P0401 in rare cases, plus it was cheap). Since I'm not ready to say it's a faulty ECU quite yet, I've begun looking into the wiring (should've done earlier). Now my current theory is that I think it may be possible that when the comp goes through the self testing it is unable to energize the VSV (vacuum switching valve). And if this is correct I would assume since the VSV is routed to the MAP sensor the sensor cannot sense the expected change in vacuum nor does the EGR valve get additional vacuum applied. It is to my understanding that the EGR under normal operation the EGR valve gets it's vacuum from the vacuum modulator which goes directly to the throttle. I'm confused as to why the system would even use the VSV other than for testing, so please correct me if I'm wrong here on my theory.

I recently got this wiring diagram (page 3 is what I'm working from)
http://socaltercel.com/manuals/paseoewd.pdf

Is this the correct diagram for my car? It seems pretty similar. I noticed some of the wiring colors are different. Also what is "L" on this diagram if it IS colors lol? I doubt it's lavender.

I have tested each VSV wire. I have confirmed continuity from one VSV solenoid wire to the #3 peg of the EFI main relay. But for some reason the other wire has continuity going to 1B and 14B of the ECU wire harness, while it should be on 15B only according to this diagram. What puzzles me tho and makes me think otherwise is that I DO NOT see the same wire colors going to this harness as I see on the VSV.

If need be I have kept a log of the last couple Freeze Frames, and notes of small modifications I have done to try to get different results. Also, I have been unable to find the vacuum hose routing diagram online. There is one under my hood so if you find it necessary I can take a pic and upload it.

I apologize for such a long post. I just really wanted whoever reading to have a thorough background of what I'm struggling with here. Am I even on the right track here? Is it possible to SAFELY run a wire straight to 15B and to see if that works without frying my ECU? Any and all help will be greatly appreciated!
 
9

·
Guest
Joined
·
0 Posts
The VSV is there to control operation of the EGR. I managed to get this code after putting in a brand new egr valve, thinking the valve itself was sticking once the motor got hot. Prior to that I had been getting a P0139 "O2 sensor circuit slow response (Bank 1 Sensor 2)" The vsv ended up being the faulty part as I had replaced the modulator as well. The frustrating part was that the vsv would pass the bench test for resistance but not work under operating conditions. A new one from rockauto is about $70.
 

·
Registered
Joined
·
21 Posts
Discussion Starter #3
Ya, I replaced mine too just in case mine was doing the same thing. However, now I have two VSV's that bench test just fine. I'm assuming you also have a 96 paseo, given your SN :D. I'm curious if you happen to have the same wiring diagram. Because if that IS the case then my wiring is wrong, which would mean a fairly easy fix.
 
9

·
Guest
Joined
·
0 Posts
I took a look at that wiring diagram you got and its not the right one. The first page shows wiring for a distributor so thats for the OBD1 gen1 5EFE. 96 and up is distributorless. The only VSV on the gen2 5E is on the right side(driver's side) of the cylinder head next to the cam position sensor. I'll see what I can dig up for you schematic wise. I'll post up later tonight.
 

·
Registered
Joined
·
21 Posts
Discussion Starter #5
Hey good eye P96! I zeroed in on the 3rd one because it said Manual Trans and had the same wire harness and completely brushed off the fishy part that it had a distributor listed. Oops. Good job.
 
9

·
Guest
Joined
·
0 Posts
Ok. Looks like I found what you need. The wire colors for the VSV are black/white and black/red. The black/red wire is tied into B+ (12 volts) along with the oxygen sensors and the under hood DLC box. With the key turned to "ON", you should be able to read 12V with the positive probe on the black/red wire and the negative probe on chassis ground. I usually run an alligator clip from the meter probe to the negative battery terminal when testing like this. The black/white wire goes back to E5/15 of the ECU. You'll have to probe from the harness connector to the ECU connector to ring out that wire for continuity. Good luck and post back what you find.
 

·
Registered
Joined
·
21 Posts
Discussion Starter #7
Confirmed 12v at B+ and black/red wire. Did you mean harness E6/15 (the smaller harness of the two)? I got continuity from Black/white to E6/15. And the color to the harness is also black/white... so I guess it's back to the drawing board for me. Idk what I could've overlooked.
 
9

·
Guest
Joined
·
0 Posts
Confirmed 12v at B+ and black/red wire. Did you mean harness E6/15 (the smaller harness of the two)? I got continuity from Black/white to E6/15. And the color to the harness is also black/white... so I guess it's back to the drawing board for me. Idk what I could've overlooked.
The wiring diagram I'm reading says E5/15, strange but ok. The neighboring wires are white and yellow, respectively. And yes, its the same black/white wire from the VSV connector all the way back to the ECU. I hate to bring up the obvious but did you check for blockages at the intake manifold port, EGR tube and cylinder head port? Also check the larger vacuum hose that plugs into the EGR and bottom of the modulator. I found a chunk of carbon lodged in that hose once. I'll look at my engine in the morning, see if I can brainstorm anything else for you. It could be a bad ECU but thats a rare thing to happen and I don't think we've ruled out everything yet.
 

·
Registered
Joined
·
21 Posts
Discussion Starter #9
Ok, so I found time to put in on the paseo this weekend. Cleaned the intake manifold out just to make sure. I've taken quite a bit of pictures of what I did so please bare with me. I did the cleaning and cleared the code but as of right now the code is on.

This is what I'm looking at as far as the electrical. From what you're describing the wiring is very different. Granted I was calling the 16 pin harness "E6" and the 26 pin "E5" as per the diagram I provided earlier (which we acknowledged was wrong anyway).

16 Pin harness with black/white VSV wire. No neighboring yellow.



and then what I was calling E5. pin 15 is blue/black



As for the blockages in the intake manifold, the previous owner had cleaned it, although it's hard to tell...













You had mentioned the cylinder head port and I was wondering what would be a safe way to clean this without flooding my engine with cleaner and carbon? It doesn't look like it would really be necessary tho.



I also checked the lower, large egr hose today and it was clear. Anyhow, thank you for all of your help so far.
 
9

·
Guest
Joined
·
0 Posts
Thanks for the pics. :D Looks like you did a great job cleaning up in there. So which wire did you confirm continuity to the VSV connector with? "Black with white stripe" in your first picture is the wire that goes to the VSV. E4 is the 26 pin connector(your 2nd pic). E5 is the 16 pin connector(your 1st pic). I'm also curoius about how the ECU is setting the code. Does it set the code immediately upon start up or does it take some driving for the CEL to come on?
 

·
Registered
Joined
·
21 Posts
Discussion Starter #11
Yes, I confirmed the black and white wire (on pin 15 of E5) goes to the VSV. The CEL only comes on after the second complete "key cycles". And what I mean by that is I have to drive it from cold to hot twice. It always comes on right as it meets that normal operating temp the second time.
 
9

·
Guest
Joined
·
0 Posts
Yes, I confirmed the black and white wire (on pin 15 of E5) goes to the VSV. The CEL only comes on after the second complete "key cycles". And what I mean by that is I have to drive it from cold to hot twice. It always comes on right as it meets that normal operating temp the second time.
Crap, that means the ECU is behaving normally. Lets try the stall test. With the car running, push up on the EGR diaphragm to actuate the valve. If the engine starts to sputter and almost stall, that will confirm everything mechanical is is working and no blockages anywhere in the EGR circuit. I would also say try re-installing your old vacuum modulator in case the new one has a problem. It may sound silly at this point but confirm that your vacuum lines are hooked up correctly, specifically the 3 lines going to the throttle body. Make sure they're in the correct order. I saw in your pic that all 3 were removed.;)
 

·
Registered
Joined
·
21 Posts
Discussion Starter #13 (Edited)
Yup... that's why I suspected wiring to ECU rather than ECU itself. Car hesitates and eventually dies depending on how much I press on the diaphragm. I have a mightyvac so I've been using that too in order to see the amount of vacuum in different parts of the system and when. I will need to check the routing off of P, E, and R of the throttle as well as replacing the old modulator when I get the chance and report back.

I'm curious, what does the P.E.R. stand for? And what should I expect from each and when (ex. more/less vacuum at WOT for... port)? From memory I think it's P. mod to E. throttle, R. mod to R. throttle, Q. mod to EGR, and P. throttle to TVV. But regardless I'll check asap :D
 
9

·
Guest
Joined
·
0 Posts
Yup... that's why I suspected wiring to ECU rather than ECU itself. Car hesitates and eventually dies depending on how much I press on the diaphragm. I have a mightyvac so I've been using that too in order to see the amount of vacuum in different parts of the system and when. I will need to check the routing off of P, E, and R of the throttle as well as replacing the old modulator when I get the chance and report back.

I'm curious, what does the P.E.R. stand for? And what should I expect from each and when (ex. more/less vacuum at WOT for... port)? From memory I think it's P. mod to E. throttle, R. mod to R. throttle, Q. mod to EGR, and P. throttle to TVV. But regardless I'll check asap :D
Ok so the EGR is working when manually actuated, good. The vacuum lines are numbered #0 #1 and #2. #0 goes on the "P" and passes the charcoal canister vapors to the TB via the TVV. #1 goes to "E" and #2 goes to "R", both of which apply vacuum to the modulator. For the P, E and R ports, make sure they're clean by spraying some throttle body cleaner into them, then blow through with compressed air. Wedge the throttle open so you can see the flow. If the TB is dirty, clean it up and make sure those tiny little ports flow well.
 

·
Registered
Joined
·
21 Posts
Discussion Starter #15
Ok, so the ports were pretty clean already but I blasted it like you said. Little carbon came out but not really enough to make a significant change in vacuum. But we shall see.

-Hose routing confirmed with what you had said and matches underhood emissions diagram.

-Reinstalled old Modulator.

-Ran engine to clear out any remaining TB cleaner.

-ECU cleared and awaiting engine to cool down in order to begin cycle tests.

As always, will report back with results.
 

·
Registered
Joined
·
21 Posts
Discussion Starter #16 (Edited)
...And it's back on. One thing I find strange is that since I cleaned out the intake manifold the CEL doesn't come on until the third drive cycle. Which isn't a huge deal but I checked the monitors' status when the light came on and it said that the EGR monitor was "ok", o2 sensor was "incomplete", and cat. was "incomplete". It used to pass the o2 sensor on the first or second cycle. Then second cycle throw the P0401 religiously and list EGR monitor as "inc." Several cycles later it would list the EGR as "ok" but keep the light on. I have NEVER seen the cat. pass its monitor test. Idk what you can make out of this information, if anything. But, I figured, any info on this phenomenon is noteworthy.

I wish this was as simple as a vacuum leak.
 
9

·
Guest
Joined
·
0 Posts
Wow. This is surely a tough one. I'm beginning to think that the ECU is being tricked into triggering the EGR code by the one of the oxygen sensors not working right. What does your scan tool say about the O2 sensor voltages? I'm more interested in the downstream sensor reading, what range are they operating in? Do you get voltage fluctuation when you rev the engine? The cat and sensors should be able to pass their I/M monitor tests, its certainly strange that the cat won't pass at all. I probably should have asked this 10 posts ago lol but how many miles on it?
 

·
Registered
Joined
·
21 Posts
Discussion Starter #18
Ya I just recently changed the o2 sensors bc I've read that certain vehicle systems (I'm not sure if paseo is one of them) will reference the o2 sensors for the testing. I've also read that in rare cases they can become slow in flipping back and forth between the voltages. Since I don't have an oscilloscope, I just replaced em anyway (not so cheap of a fix). The car is a couple hundred miles short of 195,000. It was possible that it needed new sensors anyway.

Is it possible that the cat. is bad but the computer somehow thinks it's the EGR?

The code reader I'm using is a pretty cheap and simple device. The last freeze frame I have written down is something like this:

Fuelsys1: CL
Load_PCT%: 59.6
ETC (F°): 163
Short FT1%: -2.3
Long FT1%: -2.3
MAP (inHg): 17.4
RPM: 2,615
VSS (MPH): 44
IAT (F°): 70
 
9

·
Guest
Joined
·
0 Posts
Is that freeze frame with the engine at normal operating temp? Your coolant temp reading was below normal, should be around 190-200. A bad thermostat would be a good reason why the cat soesn't pass its I/M monitor test.
 

·
Registered
Joined
·
21 Posts
Discussion Starter #20
It's the snap shot the computer took the moment it decided to trigger the CEL. So I would assume so, but I thought the computer would only self test when IT determined the engine has reached normal op temp. I'll look into that one and test the thermostat.
 
1 - 20 of 40 Posts
Top