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Old 11-08-2017, 08:33 PM   #1
dwtutts
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Default Getting code u2105

Hey guys. My wifeís Saturn is throwing a code u2105. Itís shifting hard and starting a little hard. However. I donít know if thatís is something wrong with the car or itís cold. Either way, I have done some research into it, Iíve tried doing a reset with pulling the battery out and such, but it still is shifting hard. Any ideas?

Itís a Saturn l300. 2004. 135k. V6. Thanks.

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Old 11-08-2017, 09:13 PM   #2
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Default Re: Getting code u2105

Quote:
Originally Posted by dwtutts View Post
Hey guys. My wifeís Saturn is throwing a code u2105. Itís shifting hard and starting a little hard. However. I donít know if thatís is something wrong with the car or itís cold. Either way, I have done some research into it, Iíve tried doing a reset with pulling the battery out and such, but it still is shifting hard. Any ideas?

Itís a Saturn l300. 2004. 135k. V6. Thanks.
1. Check Tranx fluid levels that could also affect hard shifts with a reliable tranx shop.
2. What proceeded this problem if any?
3. Maintenance history and repairs?
4. What did you use to read the codes if I recall they are P0 codes.

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Old 11-08-2017, 10:20 PM   #3
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Default Re: Getting code u2105

Quote:
Originally Posted by Russet View Post
1. Check Tranx fluid levels that could also affect hard shifts with a reliable tranx shop.
2. What proceeded this problem if any?
3. Maintenance history and repairs?
4. What did you use to read the codes if I recall they are P0 codes.

Seem so fine to me.

I just checked the codes after it started doing it. It was driving fine for us beforehand hand.

I change oil religiously and do all the other maintenance that I know of. Last major repair was a oil pan replacement done maybe 3 months ago.

I used an ancel ad310 classic. It did not have Saturn in it. I used the gm setting.

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Old 11-08-2017, 10:31 PM   #4
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Default Re: Getting code u2105

Quote:
Originally Posted by Russet View Post
1. Check Tranx fluid levels that could also affect hard shifts with a reliable tranx shop.
2. What proceeded this problem if any?
3. Maintenance history and repairs?
4. What did you use to read the codes if I recall they are P0 codes.
Also, I just remembered the car seemed to loose power while going through snow drifts or if it spun out on the ice. I was never driving it hard, but if you tried to push it the car would loose some power. The heater would blow much lighter, the dash lights got dim. It never stalled, just loss of power.

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Old 11-08-2017, 11:50 PM   #5
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Default Re: Getting code u2105

Anytime you drive with a car that has abs and traction control, lose traction on slippery surfaces, traction control automatically takes over for one reason. You no longer have your car under control as different wheel speeds are detected by the abs with traction control the opposite of abs, to deliberately reduce wheel spin and regain traction to all four wheels. Any one wheel not having traction means that wheel is either spinning faster or slower than the other three with abs/tc reacting. In your case the abs starts a procedure with reducing spark timing, reducing throttle (literally taking away engine power from your right foot) and in extreme cases, applies braking to remove as much wheel spinning as possible until all four wheels return to the same wheel speeds - the electronics knows the car is back to having traction at lower speed and returns throttle back to your control until you drive faster than the conditions allows normal driving. Yes, electronics are everywhere to remove power when necessary. From any abs, traction control, limp home mode from errors in drive by wire systems, and airbags. Stabilitrak removes engine power when someone makes incorrect high speed car changes in direction. The last step to removing the irresponsible driver are driverless cars being tested everywhere to see if these autonomous vehicles can handle everyday driving situations most of us take granted from years of 'practice' computers need sensors and highly developed programs. Guess how I know this? Practicing in a large parking lot with snow or ice and deliberately accelerating as fast as my car can when abs and traction control take over. I never assume a computer is smarter than me until I test it. This ads first hand experience to anyone interested while most remain clueless until experiencing it the wrong way, while driving in conditions not conducive to having complete control of a vehicle.

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Old 11-09-2017, 08:50 AM   #6
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Default Re: Getting code u2105

Before you can propose a solution, you have to know what the problem is. Your car is telling you code U2105. You need to find out what this code means. Once you know the fault, then you can determine a solution. Meanwhile you are grasping at straws.

You need to either call in one of the autostores and see if their CEL readers will diagnose a U Code OR you need to find someone with a Tech11 scanner which will certainly be able to detail the 2105 code.

Don't know if this will help

https://www.justanswer.com/saturn/2x...start-ran.html

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Old 11-09-2017, 10:02 AM   #7
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Default Re: Getting code u2105

Quote:
Originally Posted by fdryer View Post
Anytime you drive with a car that has abs and traction control, lose traction on slippery surfaces, traction control automatically takes over for one reason. You no longer have your car under control as different wheel speeds are detected by the abs with traction control the opposite of abs, to deliberately reduce wheel spin and regain traction to all four wheels. Any one wheel not having traction means that wheel is either spinning faster or slower than the other three with abs/tc reacting. In your case the abs starts a procedure with reducing spark timing, reducing throttle (literally taking away engine power from your right foot) and in extreme cases, applies braking to remove as much wheel spinning as possible until all four wheels return to the same wheel speeds - the electronics knows the car is back to having traction at lower speed and returns throttle back to your control until you drive faster than the conditions allows normal driving. Yes, electronics are everywhere to remove power when necessary. From any abs, traction control, limp home mode from errors in drive by wire systems, and airbags. Stabilitrak removes engine power when someone makes incorrect high speed car changes in direction. The last step to removing the irresponsible driver are driverless cars being tested everywhere to see if these autonomous vehicles can handle everyday driving situations most of us take granted from years of 'practice' computers need sensors and highly developed programs. Guess how I know this? Practicing in a large parking lot with snow or ice and deliberately accelerating as fast as my car can when abs and traction control take over. I never assume a computer is smarter than me until I test it. This ads first hand experience to anyone interested while most remain clueless until experiencing it the wrong way, while driving in conditions not conducive to having complete control of a vehicle.
Right and it was doing that as well which I knew was traction control, however, why would traction control dim my lights, make the fans blowing hot air half speed?

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Old 11-09-2017, 04:43 PM   #8
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Default Re: Getting code u2105

Your descriptions suggests a power issue; battery, battery cables, their connections, drive belt and tension, and alternator. All are considered parts of main power issues.

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Old 11-22-2017, 01:31 PM   #9
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Default Re: Getting code u2105

According to my 2000 L-Series FSM, Body/Electrical, vol. II, DTC U2105 is defined as "LOST COMMUNICATIONS WITH ECM." One possible repair is to replace the ECM, but that is only stated after certain tests are performed. Other than that, terminal connections at various locations are recommened to check tighteness. This relates to things fdryer has pointed out. I also agree with floridasl22002 regarding the understanding of what this DTC actually relates to so as to make an accurate diagnosis. He correctly points out that use of the GM Tech II Scan Tool, or its equivalent, is required in this instance.

I hope that the OP will keep this thread updated.

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Old 07-10-2018, 09:20 PM   #10
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Default Re: Getting code u2105

I know this thread is a few months old, but was wondering if you ever figured out this problem. I'm getting the same code and it's shifting hard as well, but starting fine. When it does shifts hard, the check engine light flashes but doesn't always leave a code. If I am in park and rev it up to around 3k the same sort of thing happens, but since I'm not in gear it seems like a misfire (the MIL light will flash on but not stay on). It only happened once on a 90 minute drive on Friday, but by the time I drove home on Saturday night, it was happening all the time, and now when I drive it, it happens all the time. I think the fluid level is fine, but I'll double check that in the morning.

I've got a 2003 LW300 automatic with 240k. Thanks in advance, you guys on this site are geniuses!

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Old 07-10-2018, 10:19 PM   #11
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Default Re: Getting code u2105

crabby, as you can see, many members neglect to reply whether or not they found a solution and share their results, even if no solution was found. This leaves many threads open.

What's important for you to know is any time you see a flashing check engine light, catalytic converter damage is imminent - a flashing engine light means excessive unburned fuel (misfiring) is entering the exhaust system and burns in the catcons. Catcons are not designed to burn fuel. They're designed to react to already burned fuel/air mixtures at high temperatures and convert exhaust byproducts into harmless CO, H2O and NOx. Burning fuel simply allows already hot catcons to ignite fuel and burn at higher temperatures, melting catcons permanently. An expensive repair to replace damaged catcons. Allowed to continue this way with a flashing check engine light and catcons can be destroyed in 50 miles.

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Old 07-11-2018, 09:05 AM   #12
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Default Re: Getting code u2105

Thanks for the reply Fdryer! After looking around on here, a clogged cat seems to describe what I've got going on. I read on here (on one of your posts actually) that you could do an 'open hole test' to confirm if it's the cats... would I do that by disconnecting the first cat from the exhaust manifold and seeing if it drives normally?

This car is my spare car I drive while I'm working on my main DD (an old 525i wagon) so I'm most likely not going to do any expensive repairs to her, but I'll definitely figure out the cheapest way to keep it going. I live in Florida so I don't have any emissions requirements to meet, and I really don't drive this car much anyway.

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Old 07-11-2018, 10:46 AM   #13
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Default Re: Getting code u2105

crabby, if clogged catcons are suspect, one way to find out is to remove the exhaust manifold O2 sensor for two open exhaust paths before the catcons. V6 engines have three catcons, one on each exhaust manifold and a third one downstream of the two. Each cylinder bank has a precat. If you can remove the exhaust manifold O2 sensor on each side of the engine, this allows two exhaust paths. You may have to use soup can diverters to direct hot exhaust gases away from nearby plastic.

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Old 07-11-2018, 11:32 AM   #14
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Default Re: Getting code u2105

Thanks for getting back- this morning after I posted that last question I actually removed the cats and drove around, but the misfire/hard shifting is still happening (just much louder!!) Thinking about it, with the exhaust off, it really felt more like misfires/engine stumbling than transmission hard shifting. Many years ago, I changed the solenoids on the transmission after getting the hard shift issue between 1/2, so I'm somewhat familiar with that problem, and additionally the wrench light hasn't come on with this problem. It still seems strange to me that the misfires or whatever is happening aren't throwing any codes.
Anyway, Fdryer thanks for the help on this and from the countless posts of yours I've used keeping this car going for so long. If you have any other ideas on what might be going on, I'll gladly take them- until then, I'll just keep troubleshooting!

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Old 07-11-2018, 04:25 PM   #15
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Default Re: Getting code u2105

With more frequent misfiring and 240k miles, old age is catching up. A fuel pressure check should be performed. Fuel filter replaced every 100k miles? Spark plugs every 100k miles? I may be wrong but I think if the engine can't run right then the xmission can't follow it so getting the engine to run right is the way to go. Once the engine runs smoothly, either the xmission shifts without harshness or continues and more troubleshooting follows to determine xmission issues.

You are correct - pressure control solenoids govern xmission shift smoothness. This presumes the electrical system is fine, the xmission control module is fine along and all the sensors on the xmission are in working order.

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Old 07-11-2018, 10:59 PM   #16
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Default Re: Getting code u2105

Got it! I remembered while I was putting everything back together this evening I read somewhere on this site (turns out it was from a conversation you were having with another user on here) where he was having the same problems and he realized that the ECU wasn't bolted on tightly. I double checked mine and sure enough, 3 of the bolts were loose, probably from the last time I did work on it (I think I did the starter and maybe the valve cover gaskets or something). They must have been working themselves loose, and the lack of ground was causing the miscommunication between the car and transmission.
I love when a problem has a simple solution (especially since my BMW is in pieces while I rebuild the rear suspension!)
Thanks for the help!

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