Tundra Conundra(um) - Limp Mode ECM Replacement? - SOLVED DTC P1126

I'll try to be brief with the backstory here as it's only slightly relevant. If you want to (potentially?) save yourself some time I'm basically in the same situation as this video (which i'll mention again later).

I bought my first truck ever a couple years ago, knowing it had a whole range of issues, from a private seller who said he had, in turn, bought it from someone else. The PO I purchased from said he didn't want to keep putting money and time into it. This is all to say two (three) things:

1. I'm an idiot who asked for this (but loves this kind of stuff)
2. I have no idea to what extent this truck has been f'd with
3. There are many issues here that may be confounding

I purchased the truck knowing all this because it is still drivable in limp mode, and all I truly need it for is getting around in around a 30 mile radius moving/hauling crap around.

That being said, as both a matter of personal pride and because it would be sweet to get to use it as a more reliable ride, I am now taking another crack at this limp mode problem.

Alright getting right into it.
2002 Tundra, Access Cab, 2UZ-FE, 4WD, Automatic Transmission (am i missing anything? 200k+ miles)

The car throws DTC P1126 "Magnetic Clutch Circuit Malfunction."
There are a few threads that mention something like it already:

• https://www.tundras.com/threads/code-p1126.34286/
• https://www.tundras.com/threads/4-7l-stuck-in-limp-mode-p1126.96465/#post-2450666
• https://www.tundras.com/threads/correct-harness-part-number-for-ecm-replacement.146791/#post-3684372

Here's a list of what I have already done:

• Purchased the 2002 FSM (idk if it's already uploaded somewhere but if people need docs lmk.)
• Cleaned the MAF
• Cleaned the Throttle Body
• Checked for corroded wires, blown fuses, etc.
• Checked the resistance of TPS, APPS (both are normal)
• Checked the operating voltages of the APPS (both myself and via techstream, all the way from released to depressed. seemingly normal voltages)
• TPS gets correct reads if i open the throttle/butterfly using that last ~1/3 of pedal from limp mode
• Checked the wire harness connectivity
• Bench tested the Magnetic Clutch and Throttle Motor (applying 5v successfully operates both functions individually, and together can open and close the butterfly).
• Replaced the throttle body anyways (also used, but specs all seem fine and bench tested fine) just in case I missed something

I would think at this point the only thing that could possibly be wrong is the ECM.

• It's the only thing I really don't think I can test.
• Looking at techstream the amperage to the magnetic clutch and throttle never move from 0A.

But I have now purchased not ONE, but TWO ECMs off eBay. I've poured over the pinouts and given that I verified the connectivity for the Throttle Control Motor/Magnetic Clutch (and the readings are showing via diagnostic, so I know the computer is reading the values correctly) I'm fairly confident that the model I'm buying (89661-0C361) is correct.

So I found this video (same as above) which basically shows the same behavior. APPS and TPS seem good, magnetic clutch and throttle operate as expected, and (spoiler) he gets the computer repaired which was a "shorted throttle body component."

My conundrum really boils down to me not having any idea what I'm doing. I've followed the manual, done all my forum searching, etc..., but at the end of the day really just know that I'm doing ALL of this for the first time. Advice desperately needed. Even if someone wants me to repeat or elaborate on certain things in this post maybe walking through it again might illuminate something, I don't know.

To conclude, my options (short of giving up, or someone catching something obvious) seem to be:

1. Pay up the money for a more reliable ECM than eBay (and just pray the almighty dollar will relinquish me)
2. Open up the ECM and stare at it with a thermal camera to see if I can find a potentially shorted component.
3. Send one of the computers to be repaired (no idea how to do that)

Thanks for any and all help! If pictures are needed of anything I'll try to find the time to get those posted.

 

Two things:

Have you tried replacing the throttle body yet? Any time I’ve seen that code here it was after an engine swap where they installed a different year engine and the pin out was wrong to the throttle body, and in other cases it was a faulty throttle body because some dumbass didn’t know you aren’t supposed to spray cleaner directly into the throttle body.

I admire the work you’ve done. Lemme see if I can find the last thread on throttle body pin out issues, since it’s relevant and we pasted a shitload of mixed year pinouts. You’re also aware of the sticky thread “so you just bought a 1st gen?”, right? It has links to download the FSM and wiring diagrams.

 

Here you go: https://www.tundras.com/threads/correct-harness-part-number-for-ecm-replacement

read that and see if it helps you - I highly, highly doubt the ECM is the problem. If you’re in question, next time, never buy your ECU off fleaBay. Buy from FS1 / Flagship One. But I *highly* doubt that’s your issue here, my friend. It’s more likely wiring, else the throttle body assembly and/or its electronics.

 

I appreciate your resolution that it isn't the ECM because I was one more bad day of troubleshooting from sinking 250 into my FOURTH ECM (from FS1 this time).

I'd read that thread and THOUGHT i checked my harness thoroughly enough, but in fact, it is EXACTLY the same CL- pin in the wrong position.

So if anyone finds this thread bashing their head against the wall because they have a semi-functional truck in limp mode:

1. Check the EWDs for ALL the pins involved in your system (in my case, it seems like I may have a 2000 Tundra wiring harness somehow).
2. After re-pinning E7(24) to E7(19) (the Lilac/Blue-White Wire) the P1126 code automatically resolved (and check engine/MIL bulb went away)

If you have no f*king idea how to re-pin like me, on that same EWD link there's a "1991 - 2005 Wire Harness Repair Manual - RM1022E." Page number 48 (50 of the PDF) gives you an idea of what you're looking at. I watched this video on youtube which shows you how to do it with a few jeweler's screwdrivers.

Now to see if other random pins are responsible for all my other electrical woes.

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EDIT: I seem to have an almost identical wiring harness. I swapped the pin mentioned above, but I am also MISSING 4 pins i'm supposed to have. I'm missing the pins for heated oxygen sensors "bank 1 sensor 2" and "bank 2 sensor 2" (which weirdly didn't throw a code until driving post limp mode fix). Those are pins E6(15), E6(16), E6(23), E6(24). I'll probably end up making a second post since this is unrelated to the limp mode fix.

 

My 2000 periodically throws a 1126 code. Several here have same and throwing parts at it doesn’t fix. What I do is clean the MAF and throttle body and also clean the electrical plugs and put a little bulb grease on them. I previously did the cowl fastener fixes when I replaced my wiper transmission. Frankly, the P1126 is unpredictable and comes and goes every couple years or so.

 

Glad you got it resolved, brother. Clearly someone swapped the engine and/or the harness at some point and/or the ECU! For what or why, the world may never know. But it’s apparently semi-common, because this is twice within a year someone has run into it and we’ve managed to solve it on this forum. If only you’d have come here sooner!

Curious to hear about any other oddities you have pop up, and work through them. I’m not great with electrical diagnostics because I suck at reading Toyota’s EWDs. It takes me 4x as long to figure this out as someone that’s competent. There are others on here way better.