[walidbatakji]

Hey guys,

I had a problem with my car a couple of days ago while driving on the highway, I felt a knock, the check engine light turned on, and I wasn't able to use the paddles, I parked aside and restarted the car, the paddles went working.
The check engine took a day later to turn off.
I put the car yesterday on the OBDII and for P0700 and P2715.
The mechanic told me that he has to change the transmission fluid.
Any suggestions? Has anyone faced this before?

[TP2SS]

There is a known issue with the 8L45/8L90 8-speed automatics with a "shuddering" feel. TSB 18-NA-355 outlines the problem, and the solution is to change the trans fluid. This issue is well documented on this forum if you search "shudder" or "18-NA-355".

Your issue doesn't sound like the shudder problem, but the mechanic is likely thinking that it is since it's the most widely known problem. I've never heard of the shudder problem throwing a code, but anything is possible I guess. If your car is still under the powertrain warranty (may be coming up on expiration soon since it's a 2017), the TSB to change the fluid should be covered. If you have to pay for it at a dealer, it should cost around $450. If it's never been done, I highly suggest you have it done whether or not it's the shudder issue you actually have. Once the shudder starts, if you don't have the fluid changed right away, you will end up with more problems later on. It's one of those things NOT to ignore for long.

[GXP08jrf]

Search this TSB as well. Sounds more like your issue than the Shudder.

#16-NA-404 - Harsh Shift, Delayed Shift, unwanted Downshift, Transmission Stuck in One Gear, Erratic Shifting, Hesitation or Have a Malfunction Indicator Lamp (MIL) Illuminated - DTC P0747, P0777, P0797, P2715 or P2724 May Be Set Current or History in Transmission Control Module - (Apr 7, 2017).

The cause is a software anomaly, the solution is to reprogram the transmission control module. Should be cheaper than getting the fluid changed if you're not experiencing the shudder.

I'd consider having the dealer do the work for both TSBs.

[walidbatakji]

Do you think it is safe to change the transmission fluid? What the mechanic exactly told me is to just drop off some of the current fluid and and on top of it new fluid (to avoid draining out the old one completely as it might cause some problems and viscosity issues)

[walidbatakji]

Will check both TSBs probably but i'm worried a little about changing the fluid.

[TP2SS]

Originally Posted by walidbatakji

Do you think it is safe to change the transmission fluid? What the mechanic exactly told me is to just drop off some of the current fluid and and on top of it new fluid (to avoid draining out the old one completely as it might cause some problems and viscosity issues)

The TSB for the shudder needs to followed exactly as described in the TSB. The full TSB even tells the dealer how to accomplish the service. This is not something you can do by yourself, or probably most mom & pop shops can do. It requires a specific procedure be followed with special fittings to flush the trans completely. It sounds like the mechanic is onboard with the flush already, so if it's a GM dealer saying this, let them do the TSB and go from there. Sounds like it may be the trans module reprogram TSB that someone noted above, but get the flush TSB done if can, regardless. It will pre-emptively fix any future shudder issue. I can't stress this enough, get the flush done per TSB 18-NA-355 and save yourself a future headache/cost.

[arpad_m]

You didn't specify mileage, but in addition to the trans flush, a diff fluid change probably wouldn't hurt either, given the age of the car.