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U0101 - Lost Communication With TCM

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U0101 - Lost Communication With TCM

Old 02-22-2016, 05:24 PM
07ChargerDude is offline
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Join Date: Feb 2016
Posts: 21
Default U0101 - Lost Communication With TCM

Only happens when cold outside.

2007, 3.5 V6 w/NAG1

I get the ESP/BAS and the CEL for U0101. DTCs must be cleared after
the engine MIL comes on, even if the problem was corrected as it warms up.
I use the tuner once it's warmed up, clear the codes, and all is normal.
The temp must be 50+ inside the car.

I can put it into gear 2-3 times, smoothly, before the ESP/BAS lights come
on for the error.

Then, when the ESP/BAS lights come on, the trans bangs into gear, and
I have no throttle in gear. It does not go into a limp mode where I can
only go 40MPH in second gear. No, I have nothing, the car will only
idle. If I step on the gas, to the floor, it will surge +200 rpm every 2 seconds,
so it just goes RRrrrrrrrrrRRrrrrrrrrRRrrrrrrrr, and so on. If I am on a
flat surface, it moves SLOW, at idle. If I start down a hill, I can speed
up and will hold that speed till it hits 40, or I stop and I got nothing again.

Basically, if this happens at a stop sign, or stop light, I ain't going anywhere.
I have to go to neutral, and go back into gear, and I have some throttle
for about 2 seconds, then it won't go past idle again. This is what leads
me to believe it is a fault in the TCM, thus losing communication with the PCM,
and not the ABS module. I read other U0101 faults, but they could at least
go about 40 in 2nd gear, not me, I have nothing when this fault shows up.

IF it is above 50 degrees outside, I don't get any problems. This happened
after letting the car sit last winter, I did not use it. It got so cold that
my AGM battery froze. Lost my TomTom GPS at the same time, the cold
must have damaged the electronics in both units? I resoldered all the
pins where the plugs go into, at the mainboard, and verified solder flow
through to the other side of the PCBoard. I do not have a small enough
iron and tip to start on the surface mounted components.

VOLTAGES at the harnesses are all normal.

Power at the C1 harness is battery voltage.
Ground at C1 is good, 0.5 ohms.
CAN C (H1/L2) at the C2 harness is 2.5 Volts, both wires.

H1/L2 on the TCM pins were also 2.5 volts, but the thing was working
at the time.

Has to be the TCM, right?
Old 03-09-2016, 05:11 AM
07ChargerDude is offline
Thread Starter
Join Date: Feb 2016
Posts: 21

Turns out, it was the TCM. IT has been warm here, so I have been starting it
up a few times a day. Well, yesterday, I thought, "cold... okay." so, I took the
TCM out and put it in the freezer for 1.5 hours, and voila, it failed... So, I need a
Old 03-18-2016, 05:27 AM
07ChargerDude is offline
Thread Starter
Join Date: Feb 2016
Posts: 21

Found one on eBay for 48.00 + shipping, so I offered $40, accepted, so I got
one for $48.50
Old 03-21-2016, 06:37 PM
07ChargerDude is offline
Thread Starter
Join Date: Feb 2016
Posts: 21

I got the TCM today, it worked after programming it with the tuner,
which was the gear ratio. It had 3.07 in it, I had to put 3.64 back.

When they sell the TCM, and tell you it may need programmed, that is
true, only if your diff gear ratio is not the same as the car the TCM
came out of. Other than that, they are plug-n-play. You do not have
to match the part numbers. The part# matches the car & carrier gear-set.
The one I bought, had a 3.07 gear ratio in it. I put it to 3.64 with the tuner,
it's fine.

It was in limp mode when I first installed it, but as able to drive in 2nd
gear, the DTC for U0101 was still stored, and the SEL was on. Cleared
that, and it ran till the engine overspeed DTC set, back to limp mode.

Plugged the tuner in, and saw the 3.07 gear ratio stored, changed it back to
3.64 for my swapped diff, and it ran fine. Also reset the adaptives as so I
am not driving with someone eles's V8 driving habits.

Also be sure, with 2007 and up you get an EGS53 TCM. 2006 only,
EGS52. The PCM and TCM communicate at different speeds between
2006 and 2007 and up, the '07 and up are faster CAN bus models,
EGS53 on the TCM label.

Additional notes (EDIT): An EGS53 will work in place of an EGS52

CAN-C bus is 500 Kbps, so there is something else different between
2006 communications, and then 2007 and up, but allows the newer
TCMs to be used.

Last edited by 07ChargerDude; 03-23-2016 at 04:36 PM.
Old 03-24-2016, 04:48 PM
07ChargerDude is offline
Thread Starter
Join Date: Feb 2016
Posts: 21

More information:

My car is a 3.5 V6, and came with 2.87 gears. I put in a 3.64 differential, for which
I needed the tuner, which also allowed me to change from 3.07 to 3.64 gears in this
TCM I bought.

I found out, with the TCM I got from an '09 R/T that, it doesn't list a 2.87 gear
ratio, the lowest it goes is 3.07. Therefore, I cannot go back to the stock carrier
if I wanted to.

So, that is another difference between models, not only years. Since the R/T
can't be ordered with anything lower than 3.07 gears, that's where the TCM
stops on the low end, and goes up to 4.10 gearing.

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