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How do I fix transmission control module communication problems.


Topic starter

Hello Scotty,

I'm from the Philippines, and I've been watching your videos and I think you have the best car related content for DIY fix in cars.

I recently bought a Chevrolet Aveo 2011 LT 1.4 A/T 150,000 km from online and I'm having some trouble with transmission. I got a check engine light and had it scanned. 
I got p0700 Transmission Control issue and a U0100

So far what I've already tried is clean the ground connector to the body so that any corrosion and dirt will be eliminated that might be doing some trouble with electricity and fortunately it eliminated  the U0100 code. But the p0700 keeps coming back.

The behavior is... the CEL will be illuminated for sometime (maybe a few days) and all of a sudden it's gone (without erasing codes)!. It will be gone also for a few day or sometimes within a day and it will come back again.

My transmission though when I have the Engine light on, is that it will sometimes jerk or clunk when I put the engine to drive or when it shift from 1st gear to 2nd gear, but this happens very rare, most of my drives are good shifting with some shifting delays (maybe about 300 - 500 (1000rpm worst) rpm late) depends on how fast from stop I'm accelerating.

I'm thinking of putting Lucas Transmission Fix first before I do anything outrageously expensive.

If you have any thoughts, I would really Appreciate it!

This is my first car, it's very hard to have a decent car here in my country especially if a newbie.

By the way all the things I know of my car came from your content! MORE POWER SCOTTY!


9 Answers

Like @itwt said, this points to an issue with the TCM. Especially because you also had that U0100 communication code in combination with that P0700 code.

As @doc said, you need to get your hands on a scanner that can read the codes in the TCM because that P0700 code says that you have at least 1. That code(s) should nail down the issue


Unfortunately, that’s the mileage when the Aveo typically starts to have transmission problems. 

Honestly, I think you bought the wrong first car. If you can sell it as-is ASAP at/near your purchase price, and buy something like the Honda Jazz or Toyota Yaris, then that would be the ideal solution.

You could try having it diagnosed by a transmission expert in your city, but I’m afraid a transmission repair might be more than what the vehicle is worth. 

The code itself points to the TCM -

All the best.


You need to get a deep scan to see what codes are in the TCM.

Doc, U0100 means a scan tool likely will not be able to talk to the TCM


Posted by: @krovax12

I got a erratic electrical problems with power windows, clocks, and radio that sometimes works and sometimes won't

This sounds like you’ve got issues in the BCM too. 

Anyway, if the U0100 comes back, check out this video -

Also, I doubt Lucas slip fix will help if the issue is with a bad solenoid or physical damage within the transmission -

Scan the TCM first to find out what the actual problem is, before your next course of action and BEFORE you start throwing parts at it.

Hello sir! Thank you so much!

I have already done this before I found this forum, turns out this one eliminated my U0100 but not the P0700.

What happened was the ground cable connectors are all dirty and the steel from the body might not be really connected with ground cables. Also I found out that there is a wandering single copper wire that was stuck on the Fan Resistor screw where all the connection is attached and was touching the body (it was about 2inch long). This fortunately eliminated U0100 code.

Also I will update from another answer in this thread what I've done so far from the last time I posted in this thread. I have also some theories.

And also sir! I found out about my Power window and Clock. It was a bad Relay when the engine is hot it fails, it seems the relay coil is getting bad.

Did replacing the relay fix the power window issue?

Posted by: @krovax12

First, this is my second account, my Krovax account has been banned for some reason I don't know.

Can you please let us know the error you face at the time of login?


Yes. Please take a screenshot and post it here.

I can't seem to upload pictures here,

But it says on every page

"You have been banned. Please contact the forum administrators for more information"

and that's all I've got.

Posted by: @krovax12

I insisted on putting Lucas Transmission Fix Last night.

additives won't do anything. There is an electronic failure, and if you don't address it, the transmission will fail completely within months. Possibly weeks.

Yeah I got that...
But if you read my explanation about it you'll understand my point...

So far, the additives did a positive job on my transmission, it won't clunk and it won't slip (maybe some minor delays on upshift and downshifts). I'm still waiting for the CEL again to light up since I added the fluid in, but so far it wasn't lighting anymore. (it's been 2days since driving from home to office and vice versa also with some minor errands)

I'm still under the impression that you are right sir. But I'll give it time before I conclude that my theory is wrong.

Thank you by the way for the advice! ^_^


Hello, Thank you for the replies! 
First, this is my second account, my Krovax account has been banned for some reason I don't know. If I could get back the account I would reply in that account for this question. (I had to make another account so that I can reply to you guys.)

First, my problem is that I can't anymore sell the car. You guys are right that I might have bought the wrong first car, but I'm still thankful that I've been learning a lot about DIY fixing and  maybe my second car I will be able to make better decisions.

About the problem:

It's bad news that it might be the mileage that the transmission is worn out already or starting to become one.
I got a in-depth scan before about this code (Think Car), and it says lost comm TCM, I'm thinking it might be electrical problem, because aside from this  I got a erratic electrical problems with power windows, clocks, and radio that sometimes works and sometimes won't (especially the power window).

I'll just have to maybe have my harness checked out first then see what happens, I'll also be trying the Lucas Transmission Fix.

If all else fails, I might be replacing the TCM (I'm going to get it first from parts out from a same year model of this car.)

Parts Out is a thing here in PH, most of us can't afford to buy GM brand new parts.

I pray that I don't have to replace my TCM because if that fails, I'll be very very sad and perhaps give this car to my brother and buy new one.

Thank you guys! 

Note: Please don't ban my account, I'm not a bot nor a spammer

This post was modified 2 weeks ago by Krovax12


Hello Guys! I insisted on putting Lucas Transmission Fix Last night.

Before I did it, I scanned for codes and I got a P0700 still and a new one U0101 (which is somewhat similar with my previous code U0100 but this time the code is pointing to the Transmission Control Module Lost Communication)

I have a theory, It seems that my TCM and ECU are fine and the CAN Bus is fine as well, it's just that what occurs to me is that when the Transmission is not engaging gears in the right time when the ECU is waiting for a response from the sensors from the transmission (controlled by the TCM) it is timing out and it will throw a error code.

To explain further, Let's say my ECU throws a request and is expecting a response for a period of time and the Transmission is late to engage gears mechanically and the sensor are delayed delivering the response then the ECU will time out and throw an error! My thinking is if I could make the transmission engage gears more accurately it might be fast enough to tell the sensors that communicates with the TCM going to ECU and the ECU will not time out.

Another thing that I think this is the case is that, I only get the CEL when I get a delay or a slip or when the TCM wants to downshift and the mechanical aspect of the transmission didn't do it on time.

Because from what I know, U0100 and U0101 will always be illuminated when the CAN BUS is really busted regardless of what is happening. My case is it will only do that if I have a slip, delay, clunk, and jerk which rare even happens.

So.... I bought the Lucas TF and add it to my ATF, Test drive it last night for 30mins without CEL and it seems the Slips and the clunking are not happening (not still 100% sure). I drove from my house to my office today about 10km this morning and no signs of anything yet and still no CEL. 

My transmission so far is running fine, though I have some delays but way lower excess RPM's (50 - 150 RPM) compared to what I had before (300-500 to 1000 rpm delay). I'm really hopeful this will last to the point I'm buying a new one.

But if this fails, God Help me.... 

NOTE: Thank you so much guys for all the help! This forum really is good community for First timers like me ^_^


Posted by: @krovax12

I can't seem to upload pictures here,

It's explained in the "READ THIS FIRST" topic.