Issues following 3.42 install
Thread Starter
Heel & Toe
Joined: Dec 2023
Posts: 23
Likes: 0
From: Atlanta, GA
Issues following 3.42 install
I have a 2003 A4 that came with the 2.73 gears. I wanted to up the performance so I purchased a low-mileage 3.42 diff from a salvaged C5 and had a reputable performance shop handle the install. I confirmed with the shop that the PCM had been recalibrated to reflect the new rear gearing. I drove the car home from the shop (20 miles) without any issues.
Two days later, I took the car on a weekend trip. The trip started normal with no issues, but after driving 100 miles I exited the highway and began experiencing very hard 1-2 shifts and somewhat hard 2-3 shifts. I switched the DIC over to the transmission temperature and noted 212* F, a little high but still within normal operating temperature (I didn’t install an external cooler when I did the 3.42 swap). I took the car out a few hours later, noted that the trans temp started in the 120s, and didn’t have the issue.
Drove home the next day. Had the cruise control set at 75 and everything seemed to be working fine until I came to some rolling hills. While on an incline the car would buck slightly, followed by a 300-500 jump in RPMs, and then the RPMs would come back down. This happened a couple times before the check engine light came on. After the check engine light came on I didn’t notice that particular issue again even when going up hills. Finished driving home and had the same hard 1-2 shift happen after exiting the highway (trans temp was 207* F). Parked the car in the garage and checked codes. P1870 was the only current code.
Just took the Vette out one more time on a short trip and didn't have any shifting issues, but it did shake a little while idling at a stoplight.
I did contact the shop to ask them and their suggestion was a full transmission rebuild by RPM. Before I go and drop that kind on money, any thoughts as to what could be causing these issues? Is the final drive ratio the only thing that needs updating in the PCM or are there other parameters that need adjusting? Are these signs of a failing torque converter or transmission? Any/all help is appreciated.
Two days later, I took the car on a weekend trip. The trip started normal with no issues, but after driving 100 miles I exited the highway and began experiencing very hard 1-2 shifts and somewhat hard 2-3 shifts. I switched the DIC over to the transmission temperature and noted 212* F, a little high but still within normal operating temperature (I didn’t install an external cooler when I did the 3.42 swap). I took the car out a few hours later, noted that the trans temp started in the 120s, and didn’t have the issue.
Drove home the next day. Had the cruise control set at 75 and everything seemed to be working fine until I came to some rolling hills. While on an incline the car would buck slightly, followed by a 300-500 jump in RPMs, and then the RPMs would come back down. This happened a couple times before the check engine light came on. After the check engine light came on I didn’t notice that particular issue again even when going up hills. Finished driving home and had the same hard 1-2 shift happen after exiting the highway (trans temp was 207* F). Parked the car in the garage and checked codes. P1870 was the only current code.
Just took the Vette out one more time on a short trip and didn't have any shifting issues, but it did shake a little while idling at a stoplight.
I did contact the shop to ask them and their suggestion was a full transmission rebuild by RPM. Before I go and drop that kind on money, any thoughts as to what could be causing these issues? Is the final drive ratio the only thing that needs updating in the PCM or are there other parameters that need adjusting? Are these signs of a failing torque converter or transmission? Any/all help is appreciated.
Drifting
Joined: Sep 2009
Posts: 1,862
Likes: 594
From: Prescott, Arizona
DTC P1870 Transmission Component Slipping
212 F and not on track suggests something slipping in the transmission generating heat.
My 2001 A4 after 120,000 miles, 10,000 wide open throttle upshifts on track would not be at that temperature on the highway.
Have a transmission shop evaluate it.
212 F and not on track suggests something slipping in the transmission generating heat.
My 2001 A4 after 120,000 miles, 10,000 wide open throttle upshifts on track would not be at that temperature on the highway.
Have a transmission shop evaluate it.
Drifting
Joined: Sep 2022
Posts: 1,373
Likes: 1,059
There are a number of parameters within the PCM that need to be changed with gearing changes.
Sounds like all they did was change the base ratio in the tune.
Definitely need to get it to a good tuning shop for a full tune.
Sounds like all they did was change the base ratio in the tune.
Definitely need to get it to a good tuning shop for a full tune.
Thread Starter
Heel & Toe
Joined: Dec 2023
Posts: 23
Likes: 0
From: Atlanta, GA
Thank you all for the help! I took it to a local transmission shop and they confirmed that the only field that was changed was the ratio change. The torque converter is not completely locking up which is causing friction and leading to the higher temps. That's throwing the code which is putting the transmission in high-pressure mode causing the hard low-speed shifts. Time to go back to the first shop!
Drifting
Joined: Sep 2022
Posts: 1,373
Likes: 1,059
Thank you all for the help! I took it to a local transmission shop and they confirmed that the only field that was changed was the ratio change. The torque converter is not completely locking up which is causing friction and leading to the higher temps. That's throwing the code which is putting the transmission in high-pressure mode causing the hard low-speed shifts. Time to go back to the first shop!
You need a tuning shop, and just go ahead and get a full tune, not just the trans tuning.
Race Director
Joined: Oct 2004
Posts: 12,860
Likes: 4,661
I wouldn't take it back to the first shop if THEY were paying ME to fix it!! They obviously don't know what the Hell they're doing. Shops get 1 chance with me. If they screw up, I don't go back for seconds.....
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Melting Slicks
Joined: Feb 2025
Posts: 2,004
Likes: 1,964
From: THE BEACH..
If you take it to that first shop I would talk to someone who can gage the competency of the person who did that tune adjustment. If they were just being lazy and just did the ratio change because the other stuff takes some time then make them do it right. You paid for it so they can do the job correctly.
Now if they completely don't know what to do, then you tell them that since they couldn't do the job completely they can give you money back or pay for it to be completed right.
Just my thoughts. That's the main reason I do my own work and tuning, I want it right.
Now if they completely don't know what to do, then you tell them that since they couldn't do the job completely they can give you money back or pay for it to be completed right.
Just my thoughts. That's the main reason I do my own work and tuning, I want it right.
Le Mans Master
Joined: Jul 2010
Posts: 6,001
Likes: 722
If you take it to that first shop I would talk to someone who can gage the competency of the person who did that tune adjustment. If they were just being lazy and just did the ratio change because the other stuff takes some time then make them do it right. You paid for it so they can do the job correctly.
Now if they completely don't know what to do, then you tell them that since they couldn't do the job completely they can give you money back or pay for it to be completed right.
Just my thoughts. That's the main reason I do my own work and tuning, I want it right.
Now if they completely don't know what to do, then you tell them that since they couldn't do the job completely they can give you money back or pay for it to be completed right.
Just my thoughts. That's the main reason I do my own work and tuning, I want it right.
Melting Slicks
Joined: Feb 2025
Posts: 2,004
Likes: 1,964
From: THE BEACH..
That's why you have someone in their management ask them what they did, if they admit to doing just the Gear Ratio change and that's it, there's how you put them on the spot. I get what you're saying but there's a way to get people to admit their wrongs.
Don't go in telling them what's wrong with the car, go in making them tell you what they did. Have them give an itemized list, then go from there. Use their own word against them.
I've done this before. Just don't do it with women.
Don't go in telling them what's wrong with the car, go in making them tell you what they did. Have them give an itemized list, then go from there. Use their own word against them.
I've done this before. Just don't do it with women.
Race Director
Joined: Oct 2004
Posts: 12,860
Likes: 4,661
Women....LMAO!! Seriously though, my main concern here would be that some damage may have occurred already. May not show up for a few thousand miles. But what they did, or actually didn't do, isn't kosher at all. Hopefully the OP didn't drive it far. Even with my 3,200 Yank converter, my trans temp rarely goes over 195°.
Burning Brakes
Joined: Jun 2022
Posts: 758
Likes: 366
I had this happen to me from a tuner that didn’t know what he was doing. The end result was a brand new vigilante converter needed rebuilt along with the transmission refreshed due to all the trash. It doesn’t take long for everything to get wrecked.
Thread Starter
Heel & Toe
Joined: Dec 2023
Posts: 23
Likes: 0
From: Atlanta, GA
I took it back to the original shop and they admitted they found some fields that needed adjusting (essentially what is found in this link). They thought that would fix the problem for good.
Got the car back and am still getting the P1870 code. I’ve driven the car more and found that the issue only happens at highway speeds when holding the throttle steady (with or without cruise control engaged) and at various temps (had it happen as low as 127*).
Does anyone have a shop they recommend in Atlanta to look into this further? Or is there anyone out there with HP Tuners willing to help me out? I’m at a loss on whether I need to go to a performance shop to fix computer programming/get a tune, or a transmission shop because I have an actual issue.
Got the car back and am still getting the P1870 code. I’ve driven the car more and found that the issue only happens at highway speeds when holding the throttle steady (with or without cruise control engaged) and at various temps (had it happen as low as 127*).
Does anyone have a shop they recommend in Atlanta to look into this further? Or is there anyone out there with HP Tuners willing to help me out? I’m at a loss on whether I need to go to a performance shop to fix computer programming/get a tune, or a transmission shop because I have an actual issue.
Thread Starter
Heel & Toe
Joined: Dec 2023
Posts: 23
Likes: 0
From: Atlanta, GA
https://www.corvetteforum.com/forums...post1608709062