2016-2017 Buick Verano 6T40 / 6T45 Transmission: Problems, Identification, and Used Replacement

Part Identification: Is This Your Transmission?

The 2016-2017 Buick Verano with the 2.4L 4-cylinder engine uses a 6-speed automatic front-wheel-drive transmission from the GM Hydra-Matic 6T40 / 6T45 family. This unit is a transaxle, which means it combines the transmission and differential into a single assembly for a front-wheel-drive vehicle.

This specific transmission is identified by the Regular Production Option (RPO) codes MH8 or MH7. These codes designate the specific version of the 6T40 family calibrated for the Verano.

Common Failure Symptoms

A failing transmission will often show clear warning signs. If you experience any of the following, it may be time to have the transmission inspected by a professional:

• Harsh, banging, or delayed shifts between gears.
• Slipping, where the engine RPMs flare up without an increase in speed (especially between 2nd and 3rd gear).
• A noticeable shudder or vibration during acceleration or at highway speeds (55-70 mph).
• Grinding or whining noises from the front of the vehicle.
• The Check Engine Light is on, especially with codes like P0700 (TCM Malfunction), P0752 (Shift Solenoid 'A' Stuck On), or P0776 (Pressure Control Solenoid Performance).

Diagnostic Flowchart

Known Issues, Recalls, and Technical Service Bulletins (TSBs)

This transmission generation has several well-documented issues, ranging from safety recalls to common mechanical wear points.

NHTSA Recall 16V-502 / 16V502000: Electronic Park Lock Lever

A severe safety recall (also tracked as GM Recall 50490 and 50491) was issued for 2016-2017 Buick Verano models because a defect could allow the ignition key to be removed when the transmission is not in the "Park" position. This creates a rollaway risk if the parking brake is not applied. The remedy involves dealers inspecting and replacing the key cylinder lock housing free of charge.

Common Mechanical & Electronic Failures

• Pressure Regulator & Pump Wear: The Generation 3 6T40 features an off-axis, chain-driven oil pump. Premature wear in the pump's pressure regulator valve bore causes internal pressure leaks, leading to slipping, burnt clutch packs, and eventually a loss of forward and reverse gears.
• TEHCM Solenoid Debris Clogging: The Transmission Electro-Hydraulic Control Module (TEHCM) is the transmission's computer, and it contains several electronic solenoids to direct fluid flow for shifting. These solenoids have fine mesh screens that are highly sensitive to microscopic metal debris. Debris causes solenoids to stick, triggering harsh shifting, gear slipping, or diagnostic trouble codes (P0700, P0752).
• Torque Converter Problems: The torque converter connects the engine to the transmission. A common failure in 6T45 units is shuddering or vibration during acceleration due to a failing torque converter lock-up clutch, leading to grinding noises.
• 6th Gear Surge/Shudder (TSB PIP6046A): Some vehicles may experience a noticeable engine surge or transmission shudder specifically in 6th gear while driving between 55 and 70 mph.
• Hard Part Failures: While more common in Generation 1 units, the 3-5-R wave plate can break, causing severe damage to the internal drum.

What Fails at Every Mileage Band

Under 60,000 Miles

Units in this range are generally in good condition but can still suffer from early electronic or torque converter issues. Known failures include torque converter shudder at light throttle (TSB PIP6046A), harsh or delayed shifts due to TEHCM software calibration issues, and transmission fluid degrading prematurely.

• ✓Do during install (required): Verify the NHTSA Recall 16V-502 for the key lock cylinder has been performed on the vehicle.
• ✓Do during install (required): Perform a full flush of the transmission cooler and lines to remove any potential factory debris.
• ✓Do during install (recommended): Ensure the latest GM software calibration is flashed to the TEHCM to address potential shift quality issues.
• ✓Do during install (recommended): Replace external seals (left and right axle shaft seals, torque converter pump seal) as a preventative measure.

60,000 to 100,000 Miles

This is where many common failures begin to surface. Torque converter failure (shuddering/grinding) and TEHCM/solenoid failures (erratic shifting, stuck gears, DTC P0776) are frequent. Shift flares and slipping between 2nd and 3rd gears due to valve body wear also appear.

• ✓Do during install (recommended): Strongly consider replacing the torque converter with an updated or remanufactured unit, especially if the original failure was shudder-related.
• ✓Do during install (recommended): If swapping a used transmission, consider swapping your original TEHCM (if functional) or purchasing a pre-programmed TEHCM to avoid programming issues.
• ✓Do during install (required): Replace all external seals and the internal filter if the pan is removed.
• ✓Do during install (required): Perform a complete DEXRON-VI fluid exchange and a TCM adaptive relearn procedure post-installation.

100,000 to 150,000 Miles

At this stage, there is an increased likelihood of complete transmission failure. Significant wear in the pressure regulator valve bore of the pump leads to pressure loss and burnt clutches. Worn transmission bands and gear wear cause slipping that fluid changes cannot fix.

• ✓Do during install (recommended): At this mileage, installing a high-quality remanufactured transmission is recommended over a used one to address known wear items.
• ✓Do during install (recommended): If using a used unit, it is critical to replace the torque converter, all seals, and the TEHCM/solenoid body.
• ✓Cheap insurance while the engine is out: Replace the engine's rear main seal while the transmission is out, as it is inexpensive and easily accessible.
• ✓Do during install (required): Mandatory comprehensive flush of the transmission cooler and lines to remove metal debris from the previous failure.

Over 150,000 Miles

Failure is highly probable if the unit is original and has not been rebuilt. Expect general wear and tear on all internal components, including clutch packs, seals, bearings, the valve body, and a high potential for broken transmission bands.

• ✓Do during install (recommended): Installation of a used transmission with over 150k miles is not recommended. A remanufactured unit with warranty is the most viable option.
• ✓Do during install (recommended): Along with the transmission, inspect and consider replacing related wear items like engine/transmission mounts and driveshaft components.
• ✓Do during install (required): Complete replacement of the transmission fluid cooler is advised over flushing if the previous failure was catastrophic, to prevent contamination.

Real Owner Experiences

Repair or Replace?

Deciding whether to repair your current transmission or replace the entire assembly depends on the specific failure and the overall condition of the unit.

When Repair Makes Sense

• TEHCM/Solenoid Malfunction (Codes P0700, P0752): This makes sense when the transmission's mechanical parts (clutches, gears) are in good condition and the issue is isolated to the valve body or its integrated computer (TEHCM). A diagnostic scan can confirm if the issue is electronic. Replacing a faulty TEHCM typically costs between $500 and $1,500. Some companies offer pre-programmed TEHCMs for $200 to $450 (part only), which can save on programming fees.
• Torque Converter Shudder/Failure: If the shudder or grinding noise is confirmed to be from the torque converter and there is no widespread debris contamination, repair is viable. A replacement remanufactured torque converter part costs between $268 and $380. The total repair cost, including labor, is usually $800 to $1,500, which is significantly less than a full replacement.
• Low or Dirty Transmission Fluid: This is a basic maintenance item and should always be the first step if shifting issues arise. A fluid and filter change costs roughly $116 to $300 and can sometimes resolve minor shifting problems or solenoid-related codes.

When Replacement is Smarter

Replacement is the smarter option when there is evidence of major internal mechanical failure, such as burnt clutches, metal debris in the pan, or multiple gear ratio errors. In these cases, the cost to disassemble and rebuild the unit with new hard parts often exceeds the price of a quality used or remanufactured transmission. A full rebuild or replacement can range from $2,000 to over $6,000.

Replacement Cost Estimates

Installation & Programming: What to Know

Professional Installation is Recommended

Replacing this transmission is an advanced to expert-level job that requires specialized tools and knowledge. It is not recommended for a DIY mechanic. Special tools required include an engine support bar or fixture to hold the engine while the subframe is lowered, a transmission jack, a torque converter holding strap/tool, and a GM-compatible scan tool (like the GM MDI with GDS2 software or a Tech 2).

Mandatory Programming

After a replacement transmission is installed, it must be programmed to work with your vehicle. You have two options:

1. Reprogram the Replacement TEHCM: A repair shop with access to GM's online programming service (SPS/TIS2WEB) must reprogram the TEHCM from the used transmission with your vehicle's VIN and software calibration.
2. Swap Your Original TEHCM: If your original TEHCM is still functional, it can be carefully removed and installed into the replacement transmission. This avoids programming fees but adds labor and risk if the original part is damaged. To do this, verify the TEHCM generation by checking the 8th digit of the barcode number on the original transmission's front cover.

After either procedure, a TCM Adaptive Relearn (also called a "Fast Learn") must be performed with a scan tool to teach the computer the specific clutch engagement points for smooth shifting.

Questions to Ask Your Installer

• Have you worked on GM 6T40/6T45 transmissions before?
• Do you have the GM MDI/MDI2 or an equivalent J2534 pass-thru tool to perform the VIN programming and TCM Adaptive Relearn?
• What is your process for flushing the transmission cooler and lines to prevent contamination?
• How do you verify the torque converter is fully seated before installation?
• Does your quote include the cost of DEXRON-VI fluid, new axle seals, and VIN programming?
• What warranty do you offer on your labor?

Freight & Delivery Reality

If you are purchasing a used 6T40/6T45 transmission online, understand that it will not arrive in a standard cardboard box via regular mail. This assembly weighs approximately 190 lbs and measures roughly 34" x 28" x 27" before crating. It ships as Less-Than-Truckload (LTL) freight strapped to a wooden pallet.

Because of its size and weight, the delivery truck will require a liftgate to lower the pallet to the ground if you are having it delivered to a residential address or a shop without a loading dock. Always perform a pre-purchase verification interview with the seller to confirm the RPO codes (MH8/MH7) and exact donor vehicle details. When the freight carrier arrives, you must inspect the transmission for physical damage (such as cracked bellhousings or broken sensors) before signing the delivery receipt. Signing without inspecting waives your right to claim shipping damage later.

Arrival Inspection for Your Used Transmission

When your used 6T40 or 6T45 transmission arrives, you must inspect it before installation. This saves time and prevents installing a broken unit.

Fluid Color and Smell

Drain a small amount of fluid from the unit. The Buick Verano uses Dexron VI transmission fluid. Healthy fluid is bright red or light brown. If the fluid is thick, black, or dark brown, the internal clutches are likely burnt. Smell the fluid. A strong, burnt toast smell confirms severe clutch damage.

Pan and Magnet Inspection

Remove the bottom transmission pan. Look at the small magnet sitting inside the pan. This magnet catches metal debris from the gears. A light coating of fine, gray paste is normal wear. If you see large metal shavings, sharp chunks, or shiny brass flakes, the transmission has internal gear or bearing damage.

Converter Hub and Input-Spline Condition

Look at the torque converter. This is the large, heavy metal bowl attached to the front of the transmission. Check the converter hub, which is the smooth metal snout that slides into the transmission pump. It must be perfectly smooth. If you feel deep scratches or grooves with your fingernail, the front seal will leak fluid.

Next, check the input shaft splines. These are the grooved teeth that connect the transmission to the engine. The teeth must be straight and evenly spaced. If the teeth are twisted, flattened, or missing, the transmission will slip or fail to move the car.

Frequently Asked Questions