Buick Lucerne's Rough Transmission Shifts Need Repair

Had similar symptoms on a 2005 Buick LaCrosse last year. The harsh shifting and delayed engagement turned out to be more complex than initially thought. The diagnostic trouble codes revealed the transmission control module was misreading signals from multiple sensors, primarily due to a failing ABS module. The root cause in my case was not the transfer case, but rather a chain reaction that started with the ABS system sending incorrect wheel speed data to the transmission control module. This caused the torque converter to engage improperly, leading to the harsh shifts. The repair required: Full system diagnostic scan, Replacement of the ABS module, Reprogramming of the transmission control module, Clearing all adaptive learning data The issue was serious because continued operation could have damaged the transmission internally. The symptoms started similarly, rough shifts, especially between 2nd and 3rd gear, with no check engine light. Would strongly recommend getting a complete diagnostic scan from a transmission specialist, as these symptoms often indicate control system issues rather than mechanical transmission problems.

Thanks for sharing that detailed experience. I had nearly identical problems on my Buick Lucerne with harsh shifting last summer. The transmission control module diagnosis caught my attention since that ended up being my culprit too, along with a faulty torque converter. I am curious what the total repair cost was in your case? Mine took a significant hit to the wallet but has been shifting smoothly ever since. Have you noticed any other transmission issues pop up since getting it fixed?

Thanks for asking about the repair costs. After seeing the mechanic, they confirmed the issue stemmed from the ABS module sending incorrect signals, which triggered the transfer case limp mode. The good news is the repair was fully covered under an extended powertrain warranty, so my total cost was zero. The mechanic found the root cause quickly because they had seen this exact issue before. Once they reprogrammed the transmission control module and cleared the fault codes, all the harsh shifting problems disappeared completely. The torque converter is now engaging properly and the transmission has been shifting like new. No transmission issues have occurred in the past year since the fix. The key was catching it early before any mechanical damage could develop. If your repair included a new torque converter, you likely wont see any more problems since that addressed the mechanical side too. Just make sure to keep up with regular transmission fluid services to protect your investment. These control module issues are fairly common but catching them early helps avoid the more expensive mechanical repairs.

After your helpful info, I finally took my Buick to a transmission specialist last week. The diagnostic scan showed problems with both the transmission control module and traction control system. The mechanic found the torque converter was starting to fail, causing the harsh shifting. The total repair came to €2800: New torque converter, Control module reprogramming, Full transmission fluid flush Been driving it for the past few days and the transmission now shifts perfectly smooth again. No more delays or rough engagement between gears. The mechanic said catching it before more internal damage occurred likely saved me from a much bigger repair bill down the road. Worth every penny to have it fixed right and avoid additional transmission problems. Really glad I got a second opinion instead of going with that first transfer case diagnosis.