4wd electrical issue

[ScubaS]

I know there are tons of "4wd not working" threads but I'm pretty sure my issue is unique. I bought my 2000 4runner limited last week with the 4wd lights flashing and it will not electronically shift into 4wd. I've run through the recommended checks and confirmed that switching vsv vacuum lines will engage 4wd so I've ruled out TC issues. The problem is that my test light shows no power to the vsv blue and brown electric plugs and the vacuum isn't being electronically switched. I also have never heard the relay click when I attempt to put it in 4wd (by button press or shifting).

Here's the unique part: The previous owner botched the install of an aftermarket alarm system. The alarm system's electrical connections were downright ugly and probably a fire hazard. I think there's a good chance that the ADD relay was destroyed due to the sketchy electrical situation but I still haven't been able to find the damn thing (I know it's somewhere on the passenger side of the steering column but haven't found it yet).

Getting to the point, other than the 4wd fuse and ADD relay are there any electrical connections that I should check that would cause a complete loss of power to the VSV connections? Also, if anyone who has actually seen the ADD relay on a 2000 limited could tell me exactly where they found it or how to positively identify it, it would be greatly appreciated.

Thanks in advance.

 

[Doc2012]

DRIVER SIDE.

Body ECU. There's a 4WD fuse in there. Check that.

Then, take the body ECU out and check the relays on the back side of that.

If that doesn't work, check the 4WD ECU on the DRIVER SIDE kick panel.

If that doesn't work, report back.

 

[TheDurk]

Pretty sure your rig should be the same as what is shown as 4wd w/2-4 selector switch in my '99 paper EWD. Like the man said, 4wd ECU is in the driver's side kick panel. It will have a black connector with 26 pins--this is no stinkin' relay--it's a computer module with relays on board.

Now please explain one thing to me. If you have no power to the VSV's on either plug, then you should have no vacuum to EITHER hose. So switching them should have ZERO effect. I really can't help you until we wrestle this one out. If you pull BOTH ADD hoses--label them first!!!--(engine running in 2wd), do you have vacuum on one, both or no hoses? How about when you pull both plugs? Now same thing in 4wd. With those answers, I can have a better idea what the issue is. To have vacuum to a hose, there has to be power to the plug, or you have a bad VSV. One or the other. Not an ECU power issue.

As far as main power to the 4wd ECU, it is a straight shot via a Black wire with white stripe from the 4wd fuse in the Body ECU, leaving at pin 1 of Plug 1J (from Cowl wire, black ten-pin plug right in center of Body ECU) passing through Junction connector J3 behind the dash and onto the 4wd ECU at pin 12 of that 26-pin connector. For fun, unplug and replug that connector. I don't know exactly why (I can guess), but this has a curative effect on many problems.

I just don't think 4wd ECU power is your problem because I don't see how the 4wd light can flash unless the 4wd ECU is functioning. That's what tells it to flash. I'd answer my questions above first, before I went chasing this power issue.

 

[ScubaS]

Thanks for the responses. I've seen the 4wd ecu but I'm not sure how to test it. The 20amp 4wd fuse in the cabin tested fine. The brown side of the vsv has vacuum and I can manually engage the tc by switching the vacuum lines (confirmed that the front drive shaft locks). Vacuum never switches from brown to blue, presumably because the signal is never sent. I don't believe the vsv unit is the issue because I've tested the plugs on the harness side and there is no response from the test light (tested blue and brown with the truck running in 2wd and 4wd).

 

[TheDurk]

Thanks for the responses. I've seen the 4wd ecu but I'm not sure how to test it. The 20amp 4wd fuse in the cabin tested fine. The brown side of the vsv has vacuum and I can manually engage the tc by switching the vacuum lines (confirmed that the front drive shaft locks). Vacuum never switches from brown to blue, presumably because the signal is never sent. I don't believe the vsv unit is the issue because I've tested the plugs on the harness side and there is no response from the test light (tested blue and brown with the truck running in 2wd and 4wd).

Sorry, but if the brown one has no power but it is passing vacuum it is bad. End of story--unless your test procedure is bad. So please, tell me if you still have vacuum on the brown side when you unplug the electrical connector on that side. Then we KNOW there is no power to the brown VSV. Sorry--it's not a lack of trust--but the data just does not compute.

 

[ScubaS]

I'll try checking it with the plug pulled tomorrow. It's possible that the vsv is bad too but I think the electrical issue remains.

Feel free to question everything I post, it makes for good problem solving. Thanks again. I'll report back on a few things tomorrow.

 

[ScubaS]

Sorry, but if the brown one has no power but it is passing vacuum it is bad. End of story--unless your test procedure is bad. So please, tell me if you still have vacuum on the brown side when you unplug the electrical connector on that side. Then we KNOW there is no power to the brown VSV. Sorry--it's not a lack of trust--but the data just does not compute.

I pulled the brown plug off and checked the vacuum over lunch today. I continue to have vacuum on the brown side when the brown electrical plug is disconnected.

So both sides of the VSV are supposed to be closed when they're not electrified? That seems a bit odd.

 

[TheDurk]

I pulled the brown plug off and checked the vacuum over lunch today. I continue to have vacuum on the brown side when the brown electrical plug is disconnected.

So both sides of the VSV are supposed to be closed when they're not electrified? That seems a bit odd.

They are completely separate components on the same bracket. Each one is a simple solenoid-actuated air valve. Power on=open. No power=closed. No cross talk between them. The 4wd ECU is supposed to do that.

So brown VSV is bad.

Now lets chase that power issue. Assuming you have confirmed power at both ends of 4wd fuse, I'd check that Black-White wire at Pin 12 of the 4wd ECU. Should have 12V+ with key on.

Pin-out of that connector is shown at F7 on page 239 here:

 

[ScubaS]

Power at both ends of the fuse has been confirmed. The black/white wire going to pin 12 of the 4wd ecu has no power with the key on.

Also, I tested the brown vsv by hooking it directly to the battery and it is functioning now. It opens with power and closes without. Maybe it was simply stuck open?

 

[TheDurk]

Power at both ends of the fuse has been confirmed. The black/white wire going to pin 12 of the 4wd ecu has no power with the key on.

Also, I tested the brown vsv by hooking it directly to the battery and it is functioning now. It opens with power and closes without. Maybe it was simply stuck open?

That would be my guess as well. Let's go with it.

So the only things in between the fuse and Pin 12 of the ECU are Plug 1J on the back of the Driver Side Fuse Panel (Pin-out on p.24 of attachment below) and the J3 Junction connector. This last looks like a beyotch to get to so lets check Plug 1J first, and thus the circuit inside the Driver Side J/B. There should be power at Pin 1 with key on. As I said, pulling and replugging the plug can sometimes fix an issue like this, as unsatisfactory as that sounds. To get to it, pull the lower finish panel by drivers knee and unbolt the fuse panel. Plug 1J is on back per diagram on p.24.

If there is power there, you have to go digging for J3, which is a blue junction connector (looks like a connector that's not connected) in the dash behind the gauges, high up and far left. Should be a few black/white wires that come together in the terminals marked "C" on p. 240 of the connector diagrams I posted above. You may have to pull the gauge panel to find it--it looks pretty buried. All that connector does is short wires together. All the black/white ones should have power with key on. Probably only two if you do NOT have Rear Diff Lock.

Good luck.

 

[ScubaS]

Sorry but I made a stupid mistake in my last post. I checked the white wire with a black stripe when I should have checked the black wire with a white stripe. The good news is that the black wire with a white stripe has power at the back of the fuse panel and at the 4wd ecu connector just as you said it should. Sorry for leading you down the wrong path on that one.

 

[TheDurk]

Sorry but I made a stupid mistake in my last post. I checked the white wire with a black stripe when I should have checked the black wire with a white stripe. The good news is that the black wire with a white stripe has power at the back of the fuse panel and at the 4wd ecu connector just as you said it should. Sorry for leading you down the wrong path on that one.

heh, I'm actually relieved. You owe me for the Excedrin headache of trying to figure out how the 4wd light could blink with no power to the 4wd ECU. I knew that was impossible.

This could now get complicated. It will require some patience. First, let's confirm that the 4wd ECU is not sending power to either VSV. The 2wd side (I forget which color VSV is which) gets power from Pin 23 of the 4wd ECU on the green/red wire. (Pin-out F7 on 239 again). The 4wd side gets power from Pin 10 on the solid light green wire. So check them both with key on in 2wd and 4wd. We need the answer to this before we can decide what to do next.

I'll scan the EWD for you when I get the chance. I have the J-shift done, but not the push button one.

 

[ScubaS]

OK, I confirmed that Pin 23 and Pin 10 are getting no power with ignition on. I tried both of them with the 4wd button depressed and released. I was very careful to test the correct connections this time.

At this point I owe you for more than excederin!

 

[TheDurk]

OK, I confirmed that Pin 23 and Pin 10 are getting no power with ignition on. I tried both of them with the 4wd button depressed and released. I was very careful to test the correct connections this time.

At this point I owe you for more than excederin!

Ok, this is a little bamboozling. You're right; this is a new issue. I would like to invite my favorite consulting forensic electron wrangler [MENTION=102597]IBallEngineer[/MENTION] to join us, as this presents a unique challenge.

Am I correct in assuming the 4wd light keeps blinking throughout all of this, or does it only blink when trying to engage 4wd? Also, what happens when you try to engage 4L? Also, please confirm my assumption that you do NOT have the rear locker?

First, lets verify we have good ground at Terminal 25 of the 4wd ECU. When something weird is happening, ALWAYS check your grounds. Also verify that one of the two pins in each VSV plug is a good ground.

Assuming those check out, lets try and confirm good conditions for 2wd. So engine running, button in 2wd position. Confirm 12V+ at Terminal 26 (yellow-black wire, H2 signal to actuator) and 13 (solid green, confirm H2 signal from actuator) of 4wd ECU.Also confirm open (no ground, no voltage) at Terminal 4 (pink wire, from 2-4 button).

If those all check out, then confirm ground at T18 (brown-yellow), open on T6 (red-blue), and check state of t19 (black-blue). These are, in order, H2 detection, L4 detection, and the ADD engage detection.

That should give us an idea. My working theory is either:

a) the inputs are so confusing the ECU doesn't know what to do, or
b) inputs are correct, so we need a new ECU.

I'll try and scan the thing tonight--couldn't do it last night.

 

[ScubaS]

The 4wd light blinks non-stop from the time the key is on from the time it is removed and everything in between. No amount of shifting changes or stops the blinking. The truck shifts into 4L but it doesn't do anything to the light. I don't think it actually goes into 4wd in 4L but I'll have to confirm that.

My truck actually has the e-locker but I've yet to even consider pushing that button so I can't report on its functionality.

For the pin results:

The VSVs both have one good ground.

4WD ECU (2wd, engine running):
T25 = good ground
T26 = nothing (checked for 12+)
T13 = nothing (checked for 12+)
T4 = nothing (checked for ground and 12+)
T6 = nothing (checked for ground and 12+)

I'll have to confirm T18 and T19 (due to my faulty memory) but I believe that I got no response when checking the ground at T18 and nothing (12+ or ground) at T19. This was also with the 2wd and engine running.

It really wouldn't surprise me if the 4wd ECU got fried when the previous owner botched the alarm system install. He stripped multiple wires and wrapped the alarm system's wires around them then simply put electrical tape over the connection. I fully removed the alarm system and taped up the exposed sections of wire but I suspect the damage was done. There was only 1 cut wire that I had to reconnect, I believe it was green with a black stripe. This was all done in the area around the body ECU and 4wd ECU.

 

[IBallEngineer]

Ok, this is a little bamboozling. You're right; this is a new issue. I would like to invite my favorite consulting forensic electron wrangler [MENTION=102597]IBallEngineer[/MENTION] to join us, as this presents a unique challenge.


That should give us an idea. My working theory is either:

a) the inputs are so confusing the ECU doesn't know what to do, or
b) inputs are correct, so we need a new ECU.

I'll try and scan the thing tonight--couldn't do it last night.

Hey thanks for the invite, I'm not up on this particular system, but you know that never stopped me from solving anything. I'm not sure I have the correct EWD either, mine is 2002.

Also, PM me to explain the ADD actuator and the Select motor, if they are applicable here.

:director:

 

[TheDurk]

Hey thanks for the invite, I'm not up on this particular system, but you know that never stopped me from solving anything. I'm not sure I have the correct EWD either, mine is 2002.

Also, PM me to explain the ADD actuator and the Select motor, if they are applicable here.

:director:

No, 2002 doesn't work because those had electric ADD actuators, and the '00 and prior used a vacuum actuator in the front diff for ADD. I'll post my '99 which is identical, as soon as I scan it.

Select motor drives the electric actuator for the 4wd in the T-case. As a 5-speed J-shift guy, I'm not real familiar with it either, but, like you, I can read an EWD. Take a look at the service notes when I post it, that pretty much explains what it does. Weird thing is the 4wd ECU should send power to either of two Vacuum Switching Valves (4wd or 2wd), and it is sending to neither.

 

[TheDurk]

The 4wd light blinks non-stop from the time the key is on from the time it is removed and everything in between. No amount of shifting changes or stops the blinking. The truck shifts into 4L but it doesn't do anything to the light. I don't think it actually goes into 4wd in 4L but I'll have to confirm that.

My truck actually has the e-locker but I've yet to even consider pushing that button so I can't report on its functionality.

For the pin results:

The VSVs both have one good ground.

4WD ECU (2wd, engine running):
T25 = good ground
T26 = nothing (checked for 12+)
T13 = nothing (checked for 12+)
T4 = nothing (checked for ground and 12+)
T6 = nothing (checked for ground and 12+)

I'll have to confirm T18 and T19 (due to my faulty memory) but I believe that I got no response when checking the ground at T18 and nothing (12+ or ground) at T19. This was also with the 2wd and engine running.

It really wouldn't surprise me if the 4wd ECU got fried when the previous owner botched the alarm system install. He stripped multiple wires and wrapped the alarm system's wires around them then simply put electrical tape over the connection. I fully removed the alarm system and taped up the exposed sections of wire but I suspect the damage was done. There was only 1 cut wire that I had to reconnect, I believe it was green with a black stripe. This was all done in the area around the body ECU and 4wd ECU.

Crap. Sorry, I missed this post. I thought [MENTION=102597]IBallEngineer[/MENTION] 's was the only new post as his started a new page and I didn't think to look back. Attached is the EWD I promised--sorry for the delay but I had some things going on.

Let me think on your results now that I've seen them.

 

[TheDurk]

OK.

I'm afraid I made a booboo. You really need to check T26 and T13 as you cycle the button from 2wd to 4wd and back. t26 should give you 3 seconds or so of 12V+ when you push the button to go into 2wd and T13 the same as you try to go into 4wd. Checking them only with the steady state flashing light they should be off so that told us nothing. My bad. I'm not familiar with this ECU as I have a nice simple 5-speed. The VSV/ADD part is the same but the T/C and the control circuitry is different.

It really would be wonderful if we had a loaner 4wd ECU to try. I'd love to rule that out. As you can see from Item 4 on p. 198, it should send 12V+ to one or the other VSV. I would think it would do this even while stuck in flashing light mode.

Can you turn the front prop shaft by hand when you push the 4wd button and leave both VSV's unplugged?

The lack of ground at T18 in 2wd suggests either a bum t/c actuator or a bad detection switch. So answer above question and that will determine which we attack first.

 

[ScubaS]

Thanks for posting the EWD. It helps me understanding what I'm actually doing.

I did a couple more quick checks over lunch. With the truck running I cycled the 4wd button and checked T26 and T13 at various intervals (checked each while engaging 2wd and 4wd). Neither terminal gave me any response.

With both VSVs unplugged (electric) and the 4wd button depressed the front prop turns freely. This doesn't surprise me because the VSVs don't have any power anyway and now that the brown VSV isn't stuck open no vacuum passes through either VSV.

Tonight I'm going to check the connections to the 4wd button just to be sure that it's actually functioning. When I bought the truck the driver's side power seat didn't work because the power wire had been severed, maybe they disconnected the 4wd selector as well.

I'm very close to just buying another 4wd ecu to try but I can't even find one for sale at the moment.