A doozy: 2UZ transmission going haywire... Until scan tool plugged in.

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eicca

Member
Messages
85
Location
Utah
This is on my parents' 1999 Land Cruiser, 4.7L 2UZ, A340F 4-speed auto box. When starting out, it shifts roughly into drive, and feels jerky and sluggish getting up to speed. It won't upshift past second, and won't engine brake when the gas is released. Then, when coming to a stop, it'll stall the motor unless it's put into neutral. I can feel the whole drivetrain bind, just like a manual if you don't open the clutch.

A video of the problems:

This started about two weeks ago, and I drove into town to look at it yesterday. Having only heard about it over the phone, I hooked up my scan tool and went for a drive. I romped it around town for thirty minutes and felt absolutely nothing wrong. So we decided to drive it this morning to the family barbecue. My dad drove, and it stalled in the first intersection and was behaving 100% messed up. I limped it back home, and noticed that the coolant gauge was spiking erratically into the red zone. So at a stop sign I hooked up my scan tool, verified that coolant temperature was actually fine, and the problems went away. When it DOES act up, the coolant gauge will jump straight to the top when turning the ignition OFF. Then it'll settle to zero. This is what pointed me in the direction of electrical issues.

I didn't correlate the scan gauge thing until this evening. I was driving it again with Techstream running, watching the transmission live data. Again, not a single issue. So at a stop sign I unplugged the OBD cable. Immediately the problems returned. No upshift past second, no engine braking, horrible lurching, and stalling out when coming to a stop. Plugged the cable back in, and it went back to normal, hitting all gears, etc. I can replicate this consistently.

Now, some important history. Our usually-trustworthy local shop botched an oil change last fall and blew up the original motor when the filter spewed. They ate it and put in a low-mileage unit for us. Today, while poking around looking for loose grounds (all of them are tight), I discovered that the ECU is not original, but "remanufactured for Toyota," PCB stamped 2004. Last time I saw the ECU was many many years ago, but I'm fairly certain it was an OEM unit with the 2UZ-FE label. Can't say for sure if the shop swapped the ECU when they did the motor, but it sure smells like it.

Does the fact that it runs totally normal ONLY with OBD scanners plugged in indicate an ECU issue? Or a short in a wire somewhere? Nothing even remotely like this happened before that motor swap, and I've never heard of anything like this from any other mechanical sources.

Odds of getting the original ECU back from the shop, if they even have it or swapped it, are not good.

Photos of the ECU:
View attachment IMG_9548.JPG
View attachment IMG_9549.JPG
 

361UZ

Member
Messages
167
Location
Canberra ACT
When you plg the scan tool in, does that put the ECU into some king of test mode, or diagnostic mode?
Or, is the scan tool grounding something that isn't when the tool is disconnected?
 

eicca

Member
Messages
85
Location
Utah
Or, is the scan tool grounding something that isn't when the tool is disconnected?

Nailed it!

I found an EWD and it revealed ground point “EC,” hidden on the back of the block, right side. The ECU grounds directly to this point. Hadn’t checked it before because I couldn’t see it. Bolt was finger loose and missing a lock washer. Replaced and tightened and we’re back to running perfect.

Connecting the scan tool seems to have redirected the ECU current to the OBD grounds.
 
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