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#3346772 - 04/18/14 05:54 PM '00 Impala LS transmission P1811
Tzu Offline


Registered: 10/12/12
Posts: 254
Loc: near Buffalo, NY
This site is very good, as I seem to be having more car issues pop up over the past month than have in the past several years. My '00 Impala 3800, 228,000 miles, literally just started having a shuddering feeling starting off from a stop and also intermittent stumble on the highway like someone turned the key off for a split second and then turned back on. I had the dealer plug into their computer to actually see what is wrong since Autozone had no check engine light as guidance. $107 later for a diagnostic fee revealed P1811 and quoted over $3,000 for a new tranny. A very good local mechanic suggested dropping pan, replacing filter and adding 24oz. of Lucas trans. additive and run it. The car is in otherwise very good condition and runs very well. I've replaced the trans. filter every 50,000 miles like clockwork as PM. Any guys out there know of ANYTHING I can do at home short of having it rebuilt? I replaced the TPS as a Buick 3800 forum pointed out as a typical cause of my symptoms, since the 3800 is a Buick design. The TCC was not the problem they said, but the TPS was. That did nothing but cost me $44, but it sounded logical. Thank you for any advice you can offer.
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#3346786 - 04/18/14 06:06 PM Re: '00 Impala LS transmission P1811 [Re: Tzu]
Brybo86 Offline


Registered: 10/08/11
Posts: 689
Loc: Chicago, IL
are you using cruise or just the pedal on the highway? about how long has the car been running when this happens?

checked the spark plug wires?

bitog link


Edited by Brybo86 (04/18/14 06:09 PM)
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#3346797 - 04/18/14 06:19 PM Re: '00 Impala LS transmission P1811 [Re: Tzu]
fdcg27 Offline


Registered: 09/25/09
Posts: 9276
Loc: OH
Wouldn't hurt to do a cooler line full flush along with a pan drop and filter replacement and nix on the Lucas.
If a cooler line full flush doesn't improve matters, then you might try some snake oil like Lucas.
As the poster above notes, this could be an ignition problem, but the shuddering you report makes me think that it probably is the tranny.
228K from a FWD automatic is a pretty good lifespan, incidentally.
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#3346804 - 04/18/14 06:28 PM Re: '00 Impala LS transmission P1811 [Re: fdcg27]
cknight49090 Offline


Registered: 01/25/14
Posts: 235
Loc: south haven mi
A shift kit may help with some of the issues check out ZZP or wbody store or 3800 performance.You can buy the shims from McMaster carr.You have to drop the pan and remove the acummulator to place the shims inside.Does it hard shift when warm?

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#3346828 - 04/18/14 06:58 PM Re: '00 Impala LS transmission P1811 [Re: Tzu]
MaxZX Offline


Registered: 04/07/10
Posts: 56
Loc: VA
Just for kicks and giggles, try unplugging the EGR sensor. Ues, it will throw a code, but see if that does anything about the shudder at speed. When I had my old Bonneville, that stopped the shudder (noticed it same as you, usually at highway speeds, especially going up a hill). I cleaned that dang EGR valve 3 times after discovering the unhook trick, but it never made a difference, so I left it disconnected and ignored the CEL.

As for the tranny, based on what I went through, I doubt that's the problem. I had the hard shift due to a bad solenoid(?) or sensor, but to replace that little part meant droppingthe tranny IIRC, so I put in a homemade shift kit (bought some nylon spacers) and didn't care about the shift anymore because it was about 90% less violent. Before that I must have drained the tranny 6 times, used the Lucas stuff and a few others, nothing made a difference.

Plenty of forums to look at, too, for more info, this is fairly common issue with that era GM car. Ponticaforum.com comes to mind, I think that's where I read a lot about this years ago.

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#3346855 - 04/18/14 07:30 PM Re: '00 Impala LS transmission P1811 [Re: Tzu]
ls1mike Offline


Registered: 06/14/08
Posts: 3057
Loc: Bremerton Wa
Shift kit install. I did this just recently. It will get you by for years.
Let me know if you have any questions.

Shift kit install
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#3346960 - 04/18/14 09:11 PM Re: '00 Impala LS transmission P1811 [Re: ls1mike]
Tzu Offline


Registered: 10/12/12
Posts: 254
Loc: near Buffalo, NY
THANKYOU for the clear and precise write up. I try to do as much as I can at home, but I'm happy there are forums with guys like you to help. Since the weather is turning warmer, I really would like to try this. If I drop the pan and there isn't a lot of material on the magnet (Oil on dipstick looks red), would the pressure control solenoid be okay? The dealer said it had long shift times which set the P1811 code. So basically this increases pressure so the pump works less hard? I am trying to fully get this before attempting to get dirty. Videos replacing the pressure solenoid looks to be so involved and one I probally would not tackle at home.Thanks again....
Originally Posted By: ls1mike
Shift kit install. I did this just recently. It will get you by for years.
Let me know if you have any questions.

Shift kit install
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#3346964 - 04/18/14 09:16 PM Re: '00 Impala LS transmission P1811 [Re: Brybo86]
Tzu Offline


Registered: 10/12/12
Posts: 254
Loc: near Buffalo, NY
I'm just driving with my foot on the gas like normal and no cruise control. Sometimes it stumbles about 5-10 minutes into the drive or after 20 miles or so. Usually the warmer the engine, the worse it bucks. I have not checked the plug wires but never thought of that. It has been running great up until recently.
Originally Posted By: Brybo86
are you using cruise or just the pedal on the highway? about how long has the car been running when this happens?

checked the spark plug wires?

bitog link
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#3346992 - 04/18/14 09:57 PM Re: '00 Impala LS transmission P1811 [Re: Tzu]
artificialist Offline


Registered: 09/23/07
Posts: 6798
Loc: Florida
If you keep the MAF sensor unplugged, the engine will run entirely off the MAP sensor, and if that eliminates problems, you know you need to replace the MAF sensor.

This works in many GM V6 engines.

TPS sensor errors will do the same thing. One good thing about having an older car is that usually you can just buy a TPS sensor. Some cars with DBW throttle bodies often require much more work, and sometimes replacement of the unit. When installing your new sensor, you may find an adjustment on it. If you do, adjust it according to the service manual, otherwise the sensor will not work correctly.

You don't need a 100% new transmission. If you get the right rebuilder, the rebuilt unit will work as well as a 100% new transmission, or even better.
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#3347308 - 04/19/14 10:08 AM Re: '00 Impala LS transmission P1811 [Re: ls1mike]
Trav Offline


Registered: 11/20/06
Posts: 9755
Loc: MA, Mittelfranken.de
Originally Posted By: ls1mike
Shift kit install. I did this just recently. It will get you by for years.
Let me know if you have any questions.

Shift kit install


+1 Thats the first thing i would try for the dreaded P1811 long shift code. Its really the only thing you can do on the transmission without getting into the weeds.
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