Electrical question

This is part of the FSM's general guide to testing for short or open circuits. What is B referring to? I have a sensor & the ECU. That's it. B?

 

The diagram is not a specific circuit/harness.
"B" represents a potential connector between two harnesses, or more accurately two harness "halves".

 

voltage check output at the ECU connector, voltage check before the harness split to see if the wire between the ECU and that connector is good and voltage check at the input to the sensor. If there is any other voltage other than +5 volts that indicates an issue. If there is less than +5 volts at the sensor the sensor readings will not be accurate.

 

There are no instructions on how one is supposed to connect two harness halves. It started with testing each harness & then went into testing both & all of a sudden B shows up.

 

The biggest reason they are testing the connector and wiring as a whole (connected) is,

When you back prob the connectors, you know there is voltage to the connector and out of the connector.

If you disconnect the connectors and test at the pins, you may show voltage. But this doesn’t mean that the connection in the connector is good. As in “it’s a bad connector”.

 

By “before the harness split" you mean disconnecting it so as to isolate.

Takes me forever to do this.... Getting access at the ECU is frustrating.... The voltage from the ECU to the sensor is supposed to be 3-3.6. Then when I apply vacuum to the sensor the voltage is supposed to drop to 1.5-2? can't quite recall, but no lower than 1.5. The initial check actually started at 2.97. I applied vacuum & got .04. Then when I released the vacuum it read 3.6.
I just checked the sensor again. I was pretty sure it came in at 5, however had not tested it both before & after the connection. Both are good. Ground is .03. The middle one, VAC? changes with & without harness. Is this significant?

 

It is much easier if you have help and jumper leads made for your Meter

Do it enough you learn the short cuts It is really nice to have a variable voltage DC power supply when you do vehicle electrical work enough makes the testing of things much easier at times.

Look around they make a nice assortment of ends and leads for your meter to help in trouble shooting these things .

Really thin leads for when back probing to not damage things.

Just what are you working on makes it much easier to have a clue what your talking about .

Please label your numbers if all numbers are Voltage Direct Current make a note .

When testing things rather then poke holes in the insulation every half inch disconnect things at the harness Connectors.

A short is current going to ground results open circuit protection or burnt wires or a visit from the fire department .

A open circuit is just that a break in the circuit from most anything corroded connections evil rodents rubbed wires or just forgetting to plug something in

 

Woke up & thought, “aha....” So this test only applies if there is an additional connection (B) in between A & C....
Thank you.... love it when something clicks.... well, hopefully I got it....

 

I'll get back to this later. I want to "get it". I started to respond, trying to be more thorough, pics, etc., however these things take longer than I think they will & I have to head out for a bit....

 

I am troubleshoting the vapor pressure sensor -

These are the instructions - below pic are my results.



Sensor unplugged - 5.2 v
Ground - .03 v
VAC? - 3.43 v (correct abreviation?)

Sensor plugged in - 5.2 v
Ground - .03 v
VAC? - 4.34 v

ECM - E1 - VC - 5.2 v

ECM - E1 - PTNK - 2.97 v
ECM - E1 - PTNK - .04 v vacuum applied to the sensor
ECM - E1 - PTNK - 3.06 v vacuum released

Sensor continuity passed - I did that last week

 

You are sure the correct amount of vacuum is being applied to much vacuum will give you incorrect results in fact lower the voltage to far. Which seems to be what your seeing.

What leads you to think the vapor pressure sensor is not working correct ??This is trouble shooting a EVAP code??

When doing electrical tests it always helps to have the battery on the charger .

 

On page # 478 or DI-218 of the manual you are using.
You’ll probably find best way to check the VPS.
Try this test, then report back.

Because it calls for different readings.
Make sure to look at the connector diagram to be sure you are checking the correct wires.

 

It was a bit frustrating trying to allow only that much vacuum, however I managed. Thing was that it did not seem to matter haow much I applied, it stayed at .04. I mean I didn't go overboard, but the voltage didn't change.

Nope no code. As I have stated, I seem to not get them when I would think I should & then when I do, it's O2 sensor.... So yeah. I just burned through me 3rd vsv for evap sensor. No code for it now. No code for it ever. So I figured I'd test the sensor since it was the last part of the canister I had not thoroughly checked. & now it seems as though there's something up after all with that low reading.... No code....

 

Ok. Took me a minute. This not having a solid grip on this stuff is not being helped by also needing to decipher which wiring I have.
This is me - (1st three pics)

Also, I see there are two tests? One with E1 (my previous post) & one with E2? The one @TnShooter was referring to (last pic in this post). Doesn't really make sense to me, However, I will attempt this with E2 tomorrow. Doesn't really change the results I got with E1 though, does it? Interesting on that last pic how the ECM has all 5 slots filled or is that typical when the diagram is from the back?

Oh, & this post feels like a mess. I don't know how else to post my wiring though.








This is not me



Different test @TnShooter was referring to

 

I will say right now I am absolutely confused. Why there are two tests in the same manual. One using E1 & the other using E2. & I am confused because I am trying to figure out my wiring & how to's from the '01 wiring manual & the '03 FSM masquerading as an'01. & that not all '01 3.4,'s have the same EVAP system. Plus I have very little idea what I am doing. I am trying like heck though....

 

Fact of life Old Toyota`s get parts that might come from anything that will work.I have worked on vehicles that needed three different EWD`s from 3 different vehicles to all be correct .

Can you see the part # of Your ECM and post that .The part #`s of your EVAP parts if possible .

That is the simple way to get an idea just what your dealing with at least to me.

Example not to be confused with your case.Interesting How a 2001 Tacoma has an engine from a 98 4Runner with the Newer Style Maf Sensor about 2 owners back it was swapped if anything was documented it was lost and not passed along. Talk about nothing making sense .

Trying to use a FSM from the wrong year can drive you nuts in the diagnostics of things.

Never causing a Evap Code to trip is interesting.

 

My vin number comes up as nonexistent at some Toyota part sites, camelback is one. Just sayin’. Another frustration....

Codes - Well it’s not that I have never had the light come on & stay on for a while & learned to ignore it. It’s just that it fixes itself so to speak. When I have had it checked, o2 sensor came up. Once, way back, I had a misfire on 3. That was an obvious issue cuz the coil was shot.
It has been on recently while I have been messing around with the EVAP stuff, but just because I have the truck running with the hoses undone. Then the light goes off after a few minutes with the hoses back on.
The vsv for EVAP will click away, loudly. Test it & it’s faulty. Air goes both ways. It’s stuck open, I guess they call it. I mean it clicks which to me just sounds like it’s opening & closing rapidly. I am a word person, so opening & closing rapidly to me does not mean stuck open.

Anyway, the last time I had the light on for any significant amount of time (it was on for a couple of months) was 5 mos ago. I know this because it went off after I changed the ps pump out & I bought it in October. Anyway, Yup. The ps pump fixed my cel.

One other thing. I have scanned the cel list & see one for the vsv being stuck closed, but not open. I could be wrong though. Like I stated, scanned. I do know something is confused somewhere along the line. I mean I just put in a new one & it’s already clicking away & tests as faulty. Air going both ways.

 

Just where are you buying valves if you had so many fail in such a short time??

Sounds like someplace got a bunch of bad valves .

I wonder do you know who had your Truck before ?

Who can say just what you have .

I can just say somethings just need to be figured out up close and in person

 

If I were doing the test.
I’d use these diagrams to test it.

I’m in the the middle of helping my brother move this weekend.
If I get a chance, I’ll try to see if I can find a way to test the VSV.
If they are burning up, they are either bad, running too long, or there is a wiring issue.

 

They are Toyota OEM. I'm just wondering if something else is causing them to fail, hence the routing around.

It was a toyota dealer truck.

I did some studying til I couldn't anymore. I have not crawled around under the dash ;ooking for ECM part number, however after looking through the manuals & more deciphering, it seems this (pic below) is me.

I did the test that @TnShooter pointed me to. -

Measure the voltage between terminals PTNK and E2 of the ECM connector.
(1) Disconnect the vacuum hose from the vapor pressure sensor.
(2) Using the MITYVAC (Hand-Held Vacuum Pump), apply a vacuum of 4.0 kPa (30 mmHg, 1.18 in.Hg) to the vapor pressure sensor.
NOTICE: The vacuum applied to the vapor pressure sensor must be less than 66.7 kPa (500 mmHg, 19.7 in.Hg).
OK: (1) Voltage: 3.0 - 3.6 V (2) Voltage: 0.5 V or less

I must apologize as I did not pay attention to the sensor harness wire colors & it is E2, not E1, that goes to it. I am still baffled as to the differing tests within the same manual though.

Measure the voltage between terminals PTNK & E1
IG switch ON 3.0 - 3.6 V
Apply vacuum 2.0 kPa (15 mmHg, 0.6 in.Hg) 1.3 - 2.1 V

Anyway, I got the same results as I did with E1 as I did with E2

Started off at 3.0 V
Applied very little vacuum - .04 V
Applied a little more vacuum - .04 V
Released vacuum - 3.36 V