2014-2017 Buick Regal 2.4L 6T40 Transmission: Problems, Identification, and Used Replacement
Identify the MH8 6-speed automatic, understand common TEHCM and torque converter failures, and learn when to install a used OEM replacement.
- A used transmission's internal control module (TEHCM) MUST be reprogrammed to your vehicle's VIN using a dealer-level tool before driving to prevent immediate damage.
- Only a transmission from a 2014–2017 Buick Regal with a 2.4L engine and FWD (RPO code MH8) is a direct fit; units from other GM models are not interchangeable.
- When installing a used unit, it is critical to flush the transmission cooler lines, replace all external seals, and consider replacing the failure-prone torque converter as preventative maintenance.
- Verify the fluid level correctly using the side check plug with the engine running and at operating temperature (185°F–203°F), as there is no dipstick and incorrect levels cause damage.
Part Identification & Verification
The transmission used in the 2014–2017 Buick Regal with the 2.4L non-turbo engine is the GM Hydra-Matic 6T40 or 6T45, a 6-speed automatic transaxle designed for front-wheel drive (FWD) vehicles. This specific unit is identified within the industry by the Regular Production Option (RPO) code MH8, though codes MH7 and MHC are also part of this family.
How to Confirm Fitment on Your Vehicle
Before purchasing a used transmission, you must verify it is the correct unit for your car. Mismatched parts will not work. Follow these steps to confirm fitment:
- Check the VIN: Confirm the 8th digit of your Vehicle Identification Number (VIN) is typically 'K' or 'R', which denotes the 2.4L non-hybrid engine.
- Check the RPO Label: Look for the Service Parts Identification label, which is a sticker usually found inside the glove box or in the trunk. Find the code MH8 on this label.
- Verify the Broadcast Code: A barcode sticker on top of the transmission case near the manual shift lever should have a four-letter code. For this specific unit, look for 4ARW or 5ARW.
- Confirm Drivetrain: Ensure your vehicle is Front-Wheel Drive (FWD). This transmission is not compatible with All-Wheel Drive (AWD) models.
- Match Part Numbers: If possible, match the original transmission's part number to known compatible numbers like 24269882 or 24269883.
What Does NOT Interchange
While other General Motors vehicles like the LaCrosse, Verano, Malibu, Equinox, and Terrain use transmissions from the same 6T40 family, they are not interchangeable with the unit from the 2.4L Regal. Differences in bellhousing bolt patterns, gear ratios, final drive codes, drivetrain configuration (AWD vs FWD), and internal computer calibrations prevent them from working correctly.
Warning: Only a transmission from a 2014–2017 Buick Regal with a 2.4L engine and FWD will fit and function correctly. Using a unit from another model will lead to installation failure or immediate performance issues.
What is Included and Excluded
When buying a used OEM transmission, industry standards (ARA URG) dictate what parts come with the assembly and what parts you must transfer from your old unit.
| Typically Included | Typically Excluded |
|---|---|
|
|
Note: The Transmission Control Module (TCM/TEHCM) is integrated into the solenoid body inside the transmission. While it is included, it is locked to the donor vehicle's VIN and must be reprogrammed before driving. 🎬 Watch: How to program a GM TCM
Common Failure Symptoms
A failing 6T40/6T45 transmission will typically show several warning signs. If you experience these issues, it may be time for a replacement.
- Shuddering or Vibration: A feeling like driving over rumble strips, especially during light acceleration or when the transmission shifts into higher gears. This is often a sign of a failing Torque Converter Clutch (TCC). 🎬 Watch: How to diagnose a transmission shudder
- Harsh or Delayed Shifts: The transmission may slam into gear, hesitate, or flare (engine RPMs rise between shifts).
- Slipping: The engine may rev higher than usual without a corresponding increase in speed, as if the transmission is struggling to stay in gear.
- Limp Mode: The vehicle may lose power and get stuck in one or two gears (often 2nd and Reverse) to prevent further damage.
- No Forward or Reverse Engagement: A complete failure to move when shifted into Drive or Reverse can indicate a severe internal problem.
Diagnostic Flowchart
Known Problems, Recalls, and Service Bulletins
Several known issues affect this transmission. Referencing the official document numbers can help a technician diagnose the problem accurately.
| Issue / TSB | Description |
|---|---|
| Shift Cable Disengagement (Recall 14048 / NHTSA 14V152000) |
On 2014 models, the shift cable adjuster can detach, causing the gear selector to show the wrong gear or fail to hold in "Park," creating a rollaway risk. The fix is to inspect and repair the adjuster. |
| Valve Body Shudder & Harsh Shifts (TSB 18-NA-358) |
Affects 2014–2017 models. A severe launch shudder or harsh 2-3 upshifts caused by debris or scoring in the valve bodies. The bulletin advises cleaning or replacing the valve bodies. |
| Snap Ring Failure (TSB 13282 / NHTSA ID 10053843) |
On 2013–2014 models, an improperly made internal snap ring can pop out, causing the transmission to enter "limp mode" with only 2nd gear and Reverse available. The solution is to replace the snap ring. |
| Driver's Side Axle Seal Leak (TSB 08-07-30-035) |
A worn case bushing allows the CV axle to wobble, tearing the seal and causing fluid leaks. The fix requires replacing the seal and installing an upgraded Teflon-coated bushing (e.g., Superior K099 kit). |
| Harsh 5-4 Downshift (Service Update 14751) |
For 2014 models (2.4L/MH8), a harsh downshift from 5th to 4th gear is resolved by reprogramming the TCM with a revised calibration. |
| Low-Mileage Harsh Shifts (TSB 14-07-30-001D) |
New or low-mileage units may exhibit harsh shifts, slips, or flares because the computer's adaptive learning is incomplete. A technician must perform a "fast learn" procedure. |
| Torque Converter Clutch (TCC) Failure | A widespread issue causing shuddering, slipping, and overheating. The failing TCC sheds metal debris, requiring replacement of the converter and a thorough system flush. |
| Internal TCM/Solenoid Failure (TEHCM) | The internal control module fails from heat and vibration, causing trouble codes (P2714, P0741, P2723), harsh shifting, or loss of gear engagement. The TEHCM must be replaced and programmed. |
What Fails at Every Mileage Band
Pro Tip: The mileage bands below describe what typically fails on used replacement units at that mileage. The checklists provided are critical steps you must take WHILE INSTALLING the purchased transmission, not general maintenance advice for your current vehicle.
Under 60,000 Miles
Transmissions in this range are generally healthy, but early failures can occur due to manufacturing defects or software issues. Shift cable disengagement (Recall 14048), snap ring failures (TSB 13282), and harsh shifts from valve body debris (TSB 18-NA-358) or incomplete adaptive learning (TSB 14-07-30-001D) are the most common complaints.
- ✓Do during install (required): Replace both CV axle seals and the front pump/torque converter seal.
- ✓Do during install (required): Ensure the shift cable recall (14048) has been performed on any 2014 model.
- ✓Do during install (recommended): Inspect the driver's side axle case bushing for any play and replace it with an upgraded Teflon-coated bushing to prevent future leaks.
60,000 - 100,000 Miles
This is where major components begin to show their age. Torque Converter Clutch (TCC) shudder often progresses to complete failure in this range. The internal TEHCM (TCM) and solenoid body frequently fail due to heat cycles, setting codes like P0741 or P2723. Catastrophic internal failures, such as a broken 3-5-Reverse wave plate, also become more common.
- ✓Do during install (required): Replace both CV axle seals and the torque converter seal.
- ✓Cheap insurance while the engine is out: Replace the torque converter itself when installing a used transmission in this mileage band. The original is a known failure point, and replacing it while the transmission is out prevents a costly repeat of the same labor.
- ✓Do during install (recommended): If the budget allows, installing a remanufactured valve body/TEHCM assembly can prevent future electronic issues.
100,000 - 150,000+ Miles
If fluid services have been neglected, this is the most common mileage range for total failure. Wear on clutch packs, shrinking bonded rubber pistons, and accumulated wear in the aluminum valve body bores lead to pressure leaks, slipping, and complete loss of gears.
- ✓Do during install (required): Replace the torque converter. It is not worth risking the original high-mileage converter.
- ✓Do during install (required): Replace all external seals (axle seals, torque converter seal).
- ✓Do during install (required): Perform a comprehensive cooler and line flush to remove all debris from the previous unit's failure.
- ✓Do during install (recommended): A used transmission in this mileage range carries high risk. Consider a professionally remanufactured unit with a warranty instead.
Real Owner Experiences
| Source | Mileage | What Happened | Cost |
|---|---|---|---|
| GM TSB 18-NA-358 | Not specified | Customer may comment on a severe launch shudder in 1st gear from a stop, or harsh shifting. The cause is debris in the valve bodies. | Covered under warranty if applicable. The repair involves replacing the upper and lower valve bodies. |
| CorvetteForum | Low mileage | A user with a new GM vehicle experienced a very rough 1-2 shift. The dealer cleared the adaptive learning values and reprogrammed the transmission according to a TSB, which resolved the issue. | Dealer programming fee, or potentially covered under warranty. |
| YouTube | 83,000 | The vehicle had no reverse gear. Teardown revealed a broken 3-5-reverse clutch wave plate, a very common problem for this transmission family. | Requires a complete transmission removal and rebuild, typically costing thousands. |
| 94,000 | Owner experienced shuddering at 2000 RPM, especially uphill. A transmission shop diagnosed a failing torque converter and preferred to replace the whole transmission. | Quoted $4,800 for a replacement transmission. | |
| BobIsTheOilGuy Forums | 100,000+ | After 100k miles of no maintenance, an owner experienced harsh downshifts and gear hunting. A professional technician noted the likely culprits are worn fluid needing a calibration reset, or an internal TEHCM issue. | Varies from a fluid/filter service and reprogram (~$200-500) to a TEHCM replacement or rebuild. |
| 130,000 | After months of intermittent shuddering that became constant, a transmission shop determined an internal failure required a full rebuild. The owner admitted fluid service had not been done. | Quoted $3,000 - $3,500 for a rebuild. | |
| Reddit Commenter | 117,000 | Commenter noted that failure around this mileage is expected if the fluid was never changed. | Implied cost of a full rebuild or replacement. |
Repair or Replace?
Deciding whether to repair your current transmission or replace it entirely depends on the specific failure and the overall condition of the unit.
When Repair Makes Sense
- Internal TEHCM/TCM Failure (Typical Cost: $600 - $900): If the vehicle has specific diagnostic trouble codes for solenoids or the control module (e.g., P2714) but otherwise shifts well mechanically, replacing just the TEHCM makes sense. A pre-programmed, refurbished TEHCM can often be accessed by removing the transmission side cover, avoiding the 8-11 hours of labor required to remove the entire transmission.
- Torque Converter Clutch Failure (Typical Cost: $800 - $1,500): If TCC shudder is caught very early and is the only symptom, replacing only the torque converter might be an option. However, this requires full transmission removal. It is only advisable if the failing converter has not circulated metal debris through the transmission.
- Valve Body Shudder (Typical Cost: $800 - $1,200): For harsh shifts directly linked to the valve body (per TSB 18-NA-358), replacing the valve body assembly is a viable repair, provided there is no evidence of clutch damage.
When Replacement is Smarter
Replacement is the smarter choice when there is evidence of internal mechanical failure (like slipping gears or metal debris in the pan), when multiple issues are present, or when the cost of a comprehensive rebuild ($3,000 - $3,500) is close to the price of a high-quality remanufactured unit. Given the high labor cost to remove and reinstall the transmission, it is often more economical to install a fully warrantied remanufactured unit (typically $2,400 - $3,200) than to risk a partial repair that may fail again.
Questions to Ask Your Installer
- Will you be performing the required VIN-specific programming (SPS2 flashing) on the TEHCM before the vehicle is driven?
- Will you also perform the "Transmission Service Fast Learn" or adaptive relearn procedure after programming?
- How do you plan to flush the transmission cooler and lines to ensure all debris from the old unit is completely removed?
- Can you confirm you are using only DEXRON-VI specification fluid?
- What is your procedure for verifying the torque converter is fully seated before mating the transmission to the engine to prevent pump damage?
- Will you inspect the driver's side axle case bushing for wear and recommend replacement if it's loose?
- How will you verify the final fluid level using the side check plug with the engine running and the fluid at the correct operating temperature (185°F–203°F)?
Replacement Cost Comparison
The cost of replacing a transmission varies based on the type of part used. Labor costs are a significant additional expense.
| Part Type | Estimated Cost (Part Only) | Notes |
|---|---|---|
| New OEM | $3,500+ | Brand new from the dealer. Often the most expensive option. |
| Remanufactured | $2,400 - $3,200 | Rebuilt in a factory with updated parts to address known flaws. Often comes with a multi-year warranty. |
| Used OEM | $475 - $1,200 | A salvaged unit from a donor vehicle. Price varies with mileage and condition. Carries more risk but is the most affordable. |
Labor Costs
Replacing this transmission is a labor-intensive job. Shops typically quote between 6.5 and 11 hours for the work. With labor rates ranging from $100 to $200 per hour, expect to pay between $975 and $2,200 for installation. Total replacement costs with a remanufactured unit can range from $3,800 to $8,000.
Installation & Programming: Critical Steps
Proper installation and programming are essential for a used transmission to work. Skipping these steps will lead to immediate failure. This job is rated as "Expert" difficulty and requires special tools, including an engine support bar, a transmission jack, a GM-compatible scan tool (GDS2 / MDI) with J2534 pass-thru, a torque wrench, an axle seal installer (J-46629-A), and a cooler line flush tool (DT-45096).
Required Consumables
- DEXRON-VI synthetic automatic transmission fluid (approx. 4.2 to 6.3 quarts for a service fill; 7.4 to 9.5 quarts for a dry fill)
- Side cover gasket (control valve body cover gasket) if opened
- Front pump / torque converter seal
- Both CV axle shaft seals
- Transmission cooler line flush (aerosol kit or dedicated flushing machine)
Required Programming (TEHCM)
Warning: A used transmission will not work until it is electronically paired to your vehicle. The internal Transmission Control Module (TEHCM) is locked to the donor vehicle's VIN. It must be programmed using a GM dealer-level scan tool (GDS2/MDI) or J2534 pass-thru tool, followed by a "Transmission Service Fast Learn" adaptive calibration. The vehicle will not start or will remain in limp mode if this is not completed. Driving without programming can burn up the clutches instantly.
Installation Gotchas
- Torque Converter Seating: The torque converter must make two distinct drops and sit about 1 inch back from the bellhousing face. Forcing the bellhousing bolts with an unseated converter will instantly crack the front pump gear.
- Dowel Pin Alignment: Ensure alignment dowel pins on the engine block are present and undamaged to prevent misalignment and rapid wear of the pump bushing or seals.
- Flush the Cooler Lines: Mandatory back-flush and forward-flush to clear metal debris from the previous failure, which will otherwise destroy the new TEHCM.
- Check Fluid Level Correctly: This transmission has no dipstick. The fluid level must be checked via the check plug on the side of the case with the vehicle level, engine running, and fluid warmed to 85°C–95°C (185°F–203°F). Checking with the engine off causes a massive underfill of 2-3 quarts.
- Use Correct Fluid: Only use DEXRON-VI synthetic automatic transmission fluid. Using universal or incorrect fluid will cause damage.
Pro Tip: Before installing the driver's side CV axle, inspect the case bushing for wear. A worn bushing will cause the new axle seal to leak almost immediately. If there is any play, replace the bushing with an upgraded Teflon-coated version.
Freight & Delivery Reality
A used 6T40 transmission is a heavy, bulky item. It weighs approximately 199 lbs and measures roughly 36" x 23" x 11" before crating. Because of its size and weight, it ships as LTL (Less Than Truckload) freight on a wooden pallet—it will NOT arrive via standard parcel services like UPS Ground or FedEx Home Delivery.
When ordering, you will likely need to request a liftgate service if delivering to a residential address without a loading dock or forklift. Always inspect the transmission thoroughly while it is still on the pallet and before signing the delivery receipt. Look for any damage to the bellhousing, electrical connectors, or pan that may have occurred during transit.
Arrival Inspection: What to Check Before Installation
- Check the Magnetic Drain Plug: The 6T40 transmission does not have a removable bottom pan. The fluid filter is hidden deep inside the case. To check for metal debris, remove the drain plug on the bottom of the transmission. This plug has a built-in magnet. A small amount of fine, dark fuzz is normal. If you see large metal shavings or chunky metal pieces, the internal gears are destroyed.
- Inspect Fluid Color and Smell: Let a few drops of fluid drip from the drain hole onto a white paper towel. Used fluid is normally dark red or light brown. If the fluid is pitch black, the internal clutches are burnt. Smell the fluid. If it smells like burnt toast, the transmission has severe heat damage.
- Examine the Torque Converter Hub: The torque converter is the large, heavy metal bowl attached to the front of the transmission. Look at the hub, which is the smooth metal tube sticking out of the back of the converter. Feel the outside of the hub with your fingernail. It must be perfectly smooth. If you feel deep scratches or grooves, the front pump seal will leak fluid.
- Check the Input Shaft Splines: Look inside the center of the torque converter to see the input shaft. The shaft has splines, which are straight metal teeth that lock into the engine. Check these teeth carefully. They must be straight and sharp. If the teeth look twisted or flattened, the transmission will slip or fail to move the car.
Frequently Asked Questions (FAQ)
Can I use a transmission from a Chevy Malibu or Equinox in my Regal?
No. While those vehicles use a similar 6T40-family transmission, they are not interchangeable due to critical differences in bellhousing bolt patterns, gear ratios, final drive codes, and electronic controls. You must use a unit from an identical 2014-2017 Buick Regal 2.4L FWD.
Do I really have to program a used transmission?
Yes, absolutely. The internal control module (TEHCM) is VIN-locked to the original car. Without reprogramming, your vehicle will either not start or will operate in a limp mode that can quickly cause permanent damage to the replacement transmission.
What kind of transmission fluid does the 2014-2017 Regal 2.4L take?
It requires DEXRON-VI synthetic automatic transmission fluid. Do not use any other type of fluid, as it can lead to poor performance and severe internal damage.
How do I check the fluid level?
There is no dipstick. The vehicle must be on a level surface with the engine running and the transmission fluid warmed to between 185°F and 203°F. A check plug on the side of the transmission case is removed, and fluid should be level with the bottom of the hole. This procedure should be performed by a qualified technician.
Why is my new transmission shifting harshly after installation?
If the transmission is mechanically sound, harsh shifts immediately after installation usually mean the "Transmission Service Fast Learn" procedure was skipped. The computer needs to be calibrated to learn the clutch adaptives of the replacement unit.
Helpful Videos
Technical Specifications
OEM Part Numbers: 24269882 24269883
Name: GM Hydra-Matic 6T40 / 6T45; Type: 6-speed automatic transaxle; Drivetrain: Front-Wheel Drive (FWD); Engine Compatibility: 2.4L non-turbo; RPO Codes: MH8 (primary), MH7, MHC; Broadcast Codes: 4ARW, 5ARW; Fluid Type: DEXRON-VI; Fluid Capacity (Dry): 7.4 to 9.5 quarts; Fluid Capacity (Service): 4.2 to 6.3 quarts; Weight: Approx. 199 lbs; Dimensions: Approx. 36" x 23" x 11"
We Have This Part in Stock
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Buick Regal:
- 🎬 Helpful Videos
- 🛍️ Shop This Part
- Part Identification & Verification
- How to Confirm Fitment on Your Vehicle
- What Does NOT Interchange
- What is Included and Excluded
- Common Failure Symptoms
- Diagnostic Flowchart
- Known Problems, Recalls, and Service Bulletins
- What Fails at Every Mileage Band
- Under 60,000 Miles
- 60,000 - 100,000 Miles
- 100,000 - 150,000+ Miles
- Real Owner Experiences
- Repair or Replace?
- When Repair Makes Sense
- When Replacement is Smarter
- Questions to Ask Your Installer
- Replacement Cost Comparison
- Labor Costs
- Installation & Programming: Critical Steps
- Required Consumables
- Required Programming (TEHCM)
- Installation Gotchas
- Freight & Delivery Reality
- Arrival Inspection: What to Check Before Installation
- Frequently Asked Questions (FAQ)
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