The Impala is acting up again.

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Some of you may recall my thread about the Impala giving us some trouble with the transmission.

'11 Impala - 3.5/4T65-E - Trans issue

We took the car to a dealership where they actually could not find anything wrong. They ended up updating the transmission computer and checked all of the motor mounts. They didn't charge us but said they were going to put it through on the powertrain warranty. I'm not sure if they did or were just being nice and ate the cost.

We initially were very happy thinking the car was fixed. But... a couple of weeks later, the car did the same "bang into gear" that it originally did. A friend of ours has an Impala that does this maybe once or twice a year, we decided to see if it happens again to see if we would take it back. Fast forward to this Monday, the car is now back to it's same old ways, banging into gear very frequently.

Today my GF calls me to tell me that she is on her way home from work. This morning, her stability control light came on, traction control light came on, and the DIC said "Engine Power Reduced". The car would not go above 20-30 MPH. She works next door to a mechanic and they took a quick look at the car, and said she should be OK to drive it home. They reset a code and the car was OK for the ride home.

So... I called another dealership today they immediately said to not drive it but have the GM Roadside Assistance tow it to them and they will diagnose the vehicle. Flat bed picked up the car a little bit ago and I guess we'll find out what's going on with it tomorrow. Guy at this dealership was nice and he understood where I was coming from. I blatantly said "I don't want this thing puking a tranny at 105k and winding up putting us on the side of the road somewhere, I've had many GM's and they've all been pretty decent." I wasn't rude to the guy and told him repeatedly how if I was expressing any aggression or anger at him that I apologize and do not mean to direct it to him. He said I wasn't so hopefully I am a calm yet stern individual. Hoping to finally get this trans. fixed and whatever this issue is (maybe related, not sure) resolved. We are going to the NHRA races in Norwalk come July and she wants to drive and take the Impala. She will be so disappointed if she can't.

Getting sick of this thing... Not trying to start any American/Import wars, believe me, but times like this make me happy that I got rid of my 2007 Impala for the 5-speed Accord.
 
You may have seen my posts about my 2005 Buick and it's transmission woes. I have saved up enough to have the transmission rebuilt. The thing that amazes me is the people who rebuild these know the problem areas. There are kits and upgraded parts made to correct the problems. Why did GM not do this??
 
Originally Posted By: 01_celica_gt
Originally Posted By: NHGUY
Chrysler A413 3spd for life....


3 speed? must be amazing gas mileage.


My 4T65e on a 3.1 Only averages 16 mpg.
 
Originally Posted By: 901Memphis
Originally Posted By: 01_celica_gt
Originally Posted By: NHGUY
Chrysler A413 3spd for life....


3 speed? must be amazing gas mileage.


My 4T65e on a 3.1 Only averages 16 mpg.

I was joking
 
Originally Posted By: 901Memphis
Originally Posted By: 01_celica_gt
Originally Posted By: NHGUY
Chrysler A413 3spd for life....


3 speed? must be amazing gas mileage.


My 4T65e on a 3.1 Only averages 16 mpg.



Huh
My hemi charger gets significantly better than that when averaging city and highway consumption.
 
I would think if it was reset at the dealer and it drove home OK, maybe there is a faulty computer that controls the shifting? Concerning my '00 Impala LS 4T65e, I had a recent diagnostic done by a dealership and they told me the trans. is worn and I would have to have a new one put in after 228,000 miles. Turns out it was a non CEL MAF sensor reading incorrectly. I didn't have all the lights you had on, but the computers do everything on cars today, so that would be my guess. I wish you luck.
 
Sounds like the pressure control module. They did an update for that part in 03 because of the constant problems with them doing that. The pressure control module doesn't work as well as it should when the trans heats up and causes some slip when shifting. The trans detects the slipping and goes into some mode for firm shifting to prevent slipping. I had an 02 Intrigue that was doing this a lot. I bought a Trans Go shift kit and installed the firmer springs for the 1-2 and 2-3 shift. $65 bucks. I installed it myself and drove it for several years without it ever doing it again. I sold the car back in March. You can replace the pressure control module, but it is mounted on the side of the trans. Huge PITA to do. I'd try the shift kit first.

EDIT: I thought your car was an 01 Impala, not an 11. I have read that even with the updated part in 03, there still are problems with the pressure control module failing. Just something to think about. Now I'm not so sure if that could be the problem or not.
frown.gif
 
Last edited:
The reduced power code is typically throttle body/TPS related and could very well give you some transmission grief. The TCM/PCM relies heavily on the engine's sensors to know what it needs to make the transmission do.
 
Originally Posted By: The_Eric
The reduced power code is typically throttle body/TPS related and could very well give you some transmission grief. The TCM/PCM relies heavily on the engine's sensors to know what it needs to make the transmission do.


Interesting, perhaps this is related to the transmission slamming into gear.

Everyone: As always I appreciate the input and comments.
 
Originally Posted By: dishdude
I suspect a bum speed sensor, not the transmission.



Me too. The trans only runs as good as the rest of the components including eng and sensors.

The "good news" is that the car finally went into a hard failure and can be diagnoses easier. The BAD news is that the mechanic he went to cleared the codes so she could drive home thus taking all the valuable evidence with it.
 
Originally Posted By: redhat
Originally Posted By: The_Eric
The reduced power code is typically throttle body/TPS related and could very well give you some transmission grief. The TCM/PCM relies heavily on the engine's sensors to know what it needs to make the transmission do.


Interesting, perhaps this is related to the transmission slamming into gear.

Everyone: As always I appreciate the input and comments.


This probably helps very little, but I had limp mode which led to hard shifting after some further driving to get home, which cleared up right after the code was cleared on our Cobalt (2006). The code I had was related to the Accelerator Pedal Position Sensor with a couple of TSBs for other stuff as well (possible leaks and bad PCM in a certain date range). Throttle body, and TCM were also among the suggestions for issues when I was poking around online.
 
Originally Posted By: GMBoy
dishdude said:
The BAD news is that the mechanic he went to cleared the codes so she could drive home thus taking all the valuable evidence with it.


The codes did not have to be cleared to make the car safe to drive home, it was already in limp mode so there was no need to clear any diagnostic codes. Another clueless tech. The dealer MAY be able to retrieve those past codes if the car holds onto them in a separate hard memory in the ECU that can be read with a GM specific scan tool. What I am saying is that the general scan tool that the mechanic used may only erase codes in soft storage.
 
Originally Posted By: Clevy
Originally Posted By: 901Memphis
Originally Posted By: 01_celica_gt
Originally Posted By: NHGUY
Chrysler A413 3spd for life....


3 speed? must be amazing gas mileage.


My 4T65e on a 3.1 Only averages 16 mpg.



Huh
My hemi charger gets significantly better than that when averaging city and highway consumption.


Must be the P0420 code plus my lead foot. Runs great except for the code and the occasional hard shifts. Plenty of power. I get 25 mpg on straight 65-70 cruising but city it abysmal. My last tank was 17 mpg but I average as low as 13-14 mpg if I idle too much. 15-16 mpg is the average with low idle time.

I don't think I'll ever have enough money to get to the bottom of the P0420 code.
 
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