How do I know if I have 6L80 or 6L90?
In most cases, you can confirm by checking the transmission model stamp or your vehicle’s official build data: the 6L90 is the heavier-duty variant used in trucks and some SUVs, while the 6L80 is the more common standard-duty version found in many GM cars and light trucks.
Where to look on the transmission
Visually identifying the model involves inspecting the transmission itself for direct markings and physical cues. The following methods are practical but not universally reliable across all model years or aftermarket work.
- Model code stamped on the case: Look along the side of the transmission housing (often near the bellhousing or main case) for a stamped or cast code that reads 6L80 or 6L90. Clean and illuminate the area to read any markings clearly.
- Transmission pan label or stamping: Some units carry a small label or engraving on the pan that indicates the transmission family or model (6L80 or 6L90). Note that not all pans will have this information.
- Dipstick tube tag or nearby serial tag: In some installations, a metal tag or stencil on the dipstick tube may display the model number. If present, this provides a quick confirmation without removing components.
- Pan design and bellhousing area: The 6L90 is the heavier-duty variant and may show a larger/deeper pan and a more robust bellhousing region. External differences are subtle and not definitive on all builds, so treat these as clues rather than proof.
These visual cues can guide you, but markings can wear off, be replaced, or be obscured in some vehicles. If markings aren’t visible or readable, move to documentation-based methods for a definitive answer.
Using the VIN, build sheet, or dealer resources
Documentation-based identification is the most reliable route. Start with the vehicle’s VIN and access to factory data, build sheets, or window stickers. The steps below outline a practical approach to obtain the exact transmission model.
VIN-based confirmation steps
- Find the VIN, typically located on the driver’s side dashboard or door jamb, and record the full 17-character code.
- Use GM’s official VIN decoding tools or request the vehicle’s build sheet/RPO data from a GM dealer. The build sheet lists the transmission specification tied to your VIN (including 6L80 or 6L90).
- Check the window sticker (Monroney label) or the owner’s manual for a transmission description. Some documents will explicitly state “Transmission: 6L80” or “Transmission: 6L90.”
- If online decoders are inconclusive, contact a GM service advisor with your VIN. They can pull factory data or RPOs from internal systems to confirm the exact model.
- Review service records or invoices for any past transmission work. If a transmission was replaced, the installed unit should be noted (6L80 vs 6L90) on the parts list or receipt.
Relying on official data from GM or a dealership minimizes confusion caused by aftermarket work, replacements, or ambiguous markings. When in doubt, verify with a trusted source.
What to ask the dealer or service advisor
When you contact a dealer or shop, provide your VIN and request the precise factory transmission specification or the corresponding RPO data. If the technician cannot access it immediately, ask them to pull a build sheet or order a copy of the customer-facing window sticker for your vehicle.
Common contextual notes
Understanding general usage can help contextualize your findings. The 6L90 is designed for higher torque and heavier-duty applications, so it appears more often in full-size trucks and some premium SUVs. The 6L80 is widely deployed across GM cars and light trucks. However, there is overlap by model year and market, so always rely on official documentation when possible.
Summary
To determine whether your GM vehicle uses a 6L80 or 6L90 transmission, start with a careful visual check of markings on the case and pan, then verify via VIN-based documentation or a build sheet from the dealer. If markings are unclear or missing, the dealer or GM service portal can confirm the exact model. Accurate identification ensures correct maintenance, parts compatibility, and service procedures.
What trucks have the 6L90 transmission?
The weight capacity and superb torque handling of the 6L90E transmission make it perform exceptionally well in construction, commercial, and industrial settings. The Chevrolet Express/GMC Savana, Chevrolet Silverado HD, and GMC Sierra HD pickups started using this model in 2007 and keep doing so even today.
What is the difference between 6L80 and 6L90?
The main difference is that the 6L90 is a heavy-duty version of the 6L80, with a longer case, stronger internal components, and a higher output torque rating. While the 6L80 is designed for applications like performance cars and light trucks, the 6L90 is built for heavier-duty use, such as in large trucks and SUVs.
You can watch this video to see the size difference between the 6L80 and 8L90 transmissions: 42sSwap TimeYouTube · Feb 19, 2020
| Feature | 6L80 | 6L90 |
|---|---|---|
| Application | Performance cars and light trucks | Heavy-duty trucks and SUVs |
| Length | Standard case | 1-3/8 inches longer than the 6L80 |
| Torque Capacity | Lower | Higher, with an output torque rating of 885 ft-lbs |
| Internal Strength | Standard | Strengthened internal components |
| Output Shaft | Typically 32-spline | Typically 29-spline, though some versions have 36-spline |
| GVW | 8,600 lbs | 15,000 lbs |
| GCVW | 14,000 lbs | 21,000 lbs |
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This video explains how to identify a 6-speed transmission: 44sCodemans autoYouTube · Nov 2, 2023
What vehicles have a 6L80E transmission?
The 6L80E transmission is found in many General Motors (GM) vehicles, including the Chevrolet Camaro SS, Corvette, Silverado 1500, Tahoe, and Suburban; GMC Sierra 1500, Yukon, and Savana vans; and Cadillac models like the Escalade, XLR, and STS. It was also used in the Hummer H2 and the Pontiac G8.
Chevrolet
- Camaro (including SS)
- Corvette
- Silverado 1500
- Tahoe
- Suburban
- Avalanche
- Express 2500/3500 Vans
- Pontiac G8
- Chevrolet SS
GMC
Sierra 1500, Yukon, Savana Vans, and Denali.
Cadillac
Escalade, STS (including STS-V), XLR (including XLR-V), and CTS-V.
Hummer
Hummer H2.
How do I tell what GM transmission I have?
You can tell what GM transmission you have by checking the ID plate on the transmission case, which provides model, part, and serial numbers, or by inspecting the shape of the transmission pan, which is often unique to the model (e.g., a TH350 pan is square with one corner missing). Another method is to look for stamped numbers on the case itself, which may include the last few digits of the VIN or other GM codes.
This video explains how to identify a GM transmission: 57sCodemans autoYouTube · Nov 2, 2023
Method 1: Check the ID plate
- Locate the small metal ID plate on the side of the transmission case, typically near the oil pan.
- The plate will have a model number, part number, and serial number printed on it. For example, "03-71" on an AW71 indicates the car has that transmission.
You can watch this video to see what a transmission tag looks like: 57sPowertrain Products IncYouTube · Dec 4, 2020
Method 2: Inspect the transmission pan
- Examine the shape of the transmission pan. Different models have distinct shapes.
- TH350: Typically has a square pan with one corner missing.
- TH400: Has a distinctive shape that resembles the state of Texas.
- Other models: Pan shape is a key identifier for many GM automatic transmissions. Counting the number of bolts can help confirm the model.
This video demonstrates the difference in pan shapes between TH350 and TH400 transmissions: 1mSpeedway MotorsYouTube · Apr 14, 2025
Method 3: Find stamped numbers on the case
- Look for a VIN (Vehicle Identification Number) or other GM codes stamped directly into the transmission case.
- This may be located on the bellhousing or near the shifter shaft.
- For example, a "1" followed by the last eight digits of the VIN can be stamped on the case.
Method 4: Use other visual cues
- For a 4L60E, look for a large electrical connector plug on the driver's side. A 700R4 has a TV cable instead and no electronic plug in the same location.
- A 6L80 transmission often has a sticker-like date tag in front of its connector, which is on the rear of the passenger's side.
