5-speed A750 trans won't shift in to 5th gear. (3 Viewers)

[LJE]

Teaching old dogs new tricks!
#1: make sure you have a battery charger on your battery while you wait the 30 minutes (saw this in a video)
#2: you'll get quite the Christmas tree when you out the key in and and turn to 'on' after jumping pins 4 and 13 on the OBD connector.

You also get a diagnostic menu for the screen/audio system. Swanky!

Now to wait 30 minutes and see if I have a 4 speed truck...

 

[Dirt J]

 

[Dirt J]

You got a 10-speed Allison now??

 

[LJE]

Well, @MongooseGA has a pretty special ECM.

It turns your 5 speed into a 4 speed, and has this cool 'catapult mode' permamently enabled. Any time the truck shifts into 1st gear (but especially when it down shifts from 2nd to 1st) it does its best to put you through the windshield - sheesh!

Made two runs with the truck with the suspect ECM - cleared codes & disconnected battery between runs. P0771 (Shift Solenoid E) fault returns.

The truck definitely tries to shift to 5th - RPMs drop momentarily, and a small lurch, but nothing actually happens. So it's not another sensor that's affecting the shift logic somewhere - the ECM is commanding 5th, but it's not happening.

I'll admit - I was highly skeptical that it was an ECM problem, but whatever output line controls Shift Solenoid E must be toast somewhere inside of it.
My guess is wherever it got sent for repair swapped out some leaky capacitors, but this fault may be internal to a microcontroller or such. Might be worth talking to the shop that did the ECM work? I can't imagine how'd you test something like this on a bench though - seems like you'd need a very specific test setup.


Other notes: truck is inexplicably drawn towards overly deep water crossings, giant boulders, and peaches. Can confirm that ECM came from Georgia.

 

[MongooseGA]

Well, @MongooseGA has a pretty special ECM.

It turns your 5 speed into a 4 speed, and has this cool 'catapult mode' permamently enabled. Any time the truck shifts into 1st gear (but especially when it down shifts from 2nd to 1st) it does its best to put you through the windshield - sheesh!

Made two runs with the truck with the suspect ECM - cleared codes & disconnected battery between runs. P0771 (Shift Solenoid E) fault returns.

The truck definitely tries to shift to 5th - RPMs drop momentarily, and a small lurch, but nothing actually happens. So it's not another sensor that's affecting the shift logic somewhere - the ECM is commanding 5th, but it's not happening.

I'll admit - I was highly skeptical that it was an ECM problem, but whatever output line controls Shift Solenoid E must be toast somewhere inside of it.
My guess is wherever it got sent for repair swapped out some leaky capacitors, but this fault may be internal to a microcontroller or such. Might be worth talking to the shop that did the ECM work? I can't imagine how'd you test something like this on a bench though - seems like you'd need a very specific test setup.


Other notes: truck is inexplicably drawn towards overly deep water crossings, giant boulders, and peaches. Can confirm that ECM came from Georgia.

Dude, this is fantastic! But what I have to know is, please tell me your truck went back to normal after testing!

Thank you thank you again!

 

[LJE]

Dude, this is fantastic! But what I have to know is, please tell me your truck went back to normal after testing!

Thank you thank you again!

I actually ran out of time (and energy - started this day halfway across the country at 0400. Flew home, ran some meetings, made dinner, then worked on the truck before putting the one year old to bed!) to throw my ECM back in there.

I wouldn't see any reason for it not to go back to normal though - I'll do that tomorrow & report back for certain.

 

[Malleus]

righteous

 

[LJE]

Confirming that everything works as expected once I dropped my ECM back in. Shifting to first is smooth, and I have 5th gear. I *did* have to repeat the pairing process with my ECM - otherwise it would crank, but not start.

One other minutia - I unplugged my throttle body during the pairing processes - it was buzzing, and I didn't want to overheat it in some way. Unnecessary? Probably, but wanted to be safe.

@MongooseGA - let me know if you want me to send it on its way back to you with the label you provided at this point, or kick it out to one of the other repair shops. I feel like I've read here on MUD that at least one shop offers some sort of 'if we can't find anything wrong with it we won't charge you' guarantee.

 

[Malleus]

teamwork

 

[emorth]

I haven't read the whole thread, so I don't know if this this will help.
I had a 1st gen 4R that would shift in and out of 5th gear at highway speed. Scary!

The engine control module will not let the transmission control module shift into 5th gear until the engine is up to normal operating temperature.

My problem was a loose connection to the temp sensor (on/off sensor not the one for the dashboard gauge) on the engine. Bad connection (disconnect) would make the engine controller think the engine was cold and it would tell the trans controller to shift out of 5th gear - at 60MPH. Hit another bump in the road, the connection would reconnect and the engine controller would think the engine was at operating temp and would tell the trans controller it was ok to shift into 5th gear. It took a while and lots of electronic test equipment (including an oscilloscope) to discover what was going on.

Fixed the bad connection to the temperature sensor, never had a problem after that.

I feel sorry for the previous owner, he told me before I bought the 4R that he spent $$$$$$ at a transmission shop and they could never fix it. So sad. All I had to do was crush the connector a little bit to make a tighter fit to the temp sensor. Done!

Hope this helps.

 

[MongooseGA]

Confirming that everything works as expected once I dropped my ECM back in. Shifting to first is smooth, and I have 5th gear. I *did* have to repeat the pairing process with my ECM - otherwise it would crank, but not start.

One other minutia - I unplugged my throttle body during the pairing processes - it was buzzing, and I didn't want to overheat it in some way. Unnecessary? Probably, but wanted to be safe.

@MongooseGA - let me know if you want me to send it on its way back to you with the label you provided at this point, or kick it out to one of the other repair shops. I feel like I've read here on MUD that at least one shop offers some sort of 'if we can't find anything wrong with it we won't charge you' guarantee.

Great news that yours went back to normal.

Yeah if we can figure out who that guy is that rebuild, I'm totally up for that. I'll provide a shipping label if that's the strategy. Worst case, I know what good used ones run.

 

[LJE]

Based on this thread (2007 LC - Replace ECM - https://forum.ih8mud.com/threads/2007-lc-replace-ecm.1123347/), these are the folks that do it: Lexus - https://www.g7computers.com/collections/vehicle-computer-repair-service/products/lexus-computer-repair

But, at $425, that's not cheap. There's a used ECM for $250 with the same part number on the 'bay right now...

Another option (that you've previously identified) is these folks for ~$180 - although, they don't have the LX470 explicitly listed: Lexus ECM / ECU Repair & Return Archives - SIA Electronics - https://siaelec.com/product-category/ecm-ecu-repair-return/lexus-ecm-ecu-repair-return/

Or, as mentioned before, might be worth giving the shop that 'fixed' it the first time for you another shout and ask what they did. At the very least, that would let you talk to SIA or G7 to give them a better idea of if they can fix it or not.

 

[jpneely]

Thanks guys for following this one though. I’ve really enjoyed these few days of thoughtful reading. I hope resolution is found and it’s not too painful!

 

[2001LC]

No 5th gear. P0771 keeps retuning!

Confirmed ECT reading correct, through to OBDII port. Engine runs with acceptable ECT ranger ~197F, for year.
Confirmed ECM working by swapping into @LJE 100 series. WRONG CONFIRMED BAD ECU
Confirm AT, valves, speed sensor all good. By testing and swapping in replacement AT.
Confirmed AT fluid to proper level and AT running in normal operating temps.
Confirmed all wire housing blocks connected.

Crank position sensor wire condition, NOT confirmed, no DTC indication Crank position sensor has any issue.

NOTES:
WIRE HOUSING BLOCK UNDER HEATER TEES, CRUD!
TC replace, long before issue of 5th.

 

[LJE]

No 5th gear. P0771 keeps retuning!

Confirmed ECT reading correct, through to OBDII port. Engine runs with acceptable ECT ranger ~197F, for year.
Confirmed ECM working by swapping into @LJE 100 series.
Confirm AT, valves, speed sensor all good. By testing and swapping in replacement AT.
Confirmed AT fluid to proper level and AT running in normal operating temps.
Confirmed all wire housing blocks connected.

Crank position sensor wire condition, NOT confirmed, no DTC indication Crank position sensor has any issue.

NOTES:
WIRE HOUSING BLOCK UNDER HEATER TEES, CRUD!
TC replace, long before issue of 5th.

That's incorrect - we confirmed that Mongoose's ECM is nonfunctional by swapping it into my LX470. If I install his ECM in my truck, I get his exact symptoms.

 

[GTV]

I'm stoked the mud community came together to figure this out! I wish I could have contributed but this topic is way above my pay grade.

 

[MongooseGA]

I'm stoked the mud community came together to figure this out! I wish I could have contributed but this topic is way above my pay grade.

Yo tambien.

I'd be lying if I said I hadn't shopped replacements for Gerry during this time. Big leader in my search has been a Powerstroke Excursion. But you know what? I'd lose this community and a ton of my friends today are Cruiser- derived. The helpfulness of this forum, and guys like all who have been posting continuously in this thread, are seriously reason enough not to want to be out of a Cruiser.

Not to mention, they're the best trucks, even with bad sensors and ECMs

I've got 2 more days in Costa Rica and when we get home, Gerry gets a new brain, and my life will feel complete again.

 

[MongooseGA]

I did a deep dive shop yesterday, looking for ECMs online. At this time, a used one was in the cards for me, and I'm considerate that it's possible used items are bad. Unfortunately, all recyclers sell electronics 'as-is', meaning if the unit is bad, I'm just out that purchase. I found one on eBay listed at $250 shipped, messaged the seller to confirm his 'no return' policy. As luck would have it, this particular seller pulled this particular ECM out of his own personal vehicle which one of his sons recently wrecked. Known good unit, and if for some reason it doesn't work, he'll take it back in return. Score! I'd also seen that he had it on promo for $225 while I was abroad, so I asked him about it, and he made the reduction as well. Double score!

Unit should be here soon and hopefully we can put this issue to bed. Good timing, as I need to do truck stuff.

 

[2001LC]

One thing I do and Toyota Tech training teaches. Is look for why a failure occurred. It's rare to have a defect in a 100 series part, but does happens. But when they happen, usually in first few year/50K miles. For you to have a ECM failure, is unusual.

Can you think of anything, that may have shorted the ECM?

One thing I try not to forget to do, is disconnect battery negative post. When servicing any electrical/electronic. This includes unplugging/plugging in a wire housing blocks. Keep in mind it's a highly integrated system and even lights are live, key off.

 

[J1000]

Awesome work, guys! The ECM was also one of the last things on my list but glad you were able to reproduce the issue and figure it out!