8L45 Valve Body 2015

2015 was the first model year GM built the 8L45 and the related 8L90, so a valve body for a 2015 Colorado, Canyon, ATS, CTS or similar is the earliest production casting in this 8-speed family, before any of the running changes made in later years. This listing is a TransGo-brand replacement built for that launch-year unit, aimed at trucks and cars showing harsh or flared shifts, slipping under load, converter shudder, or a stored pressure or solenoid code.

What the valve body does in the launch-year 8L45

The 8L45 is GM's lighter-duty 8-speed, running under RPO codes M5N and M5T behind four- and six-cylinder vehicles, while the related 8L90 (RPO M5U/M5X) carries the same hydraulic architecture behind V8 trucks and the Corvette. The valve body routes line pressure through precision bores and spool valves to each clutch pack and band, and carries the pressure-control and shift solenoids the TCM uses to time every shift. Because 2015 is the launch year, this casting is also the baseline every later production change on this family was measured against, so a bore wearing out of spec here shows up as an immediate shift complaint rather than a gradual fade.

Symptoms on this year and application

• Harsh, late or flared shifts, often worse cold
• Slipping between gears or a missing upshift
• Torque converter clutch shudder or slip at light throttle
• Limp mode with a stored pressure-control or shift-solenoid circuit code

How to confirm it before you order

Sonnax's troubleshooting notes on this family describe a no-move or no-pressure condition traced to the chain-driven pump failing to prime off-axis, which looks like a dead valve body but is a separate priming fault with its own bench-prime procedure - worth ruling out before you buy a replacement valve body for a no-move complaint. For a shift-shudder complaint specifically, GM's Service Bulletin 18-NA-355 calls for a fluid change to Mobil 1 Synthetic LV ATF HP across this 8-speed family before any parts are replaced. Scan for codes and review our 8L90/8L45 valve body symptoms and testing guide alongside the 8L90 common problems and fixes guide to narrow down which of these is actually happening on your vehicle.

Fitment

This listing is built specifically for the 2015 launch-year casting. GM made running changes to this valve body in subsequent years, so match the connector count and casting marks on your original unit against the listing photos before ordering, or send your year, make, model and VIN so we can confirm fitment. If your vehicle is a 2017 model year instead, our 8L45 valve body 2017 listing is built for that later casting, and the full 8L90/8L45 parts collection covers every other part sold for this transmission family.

Install notes

Change the fluid and filter at the same time as the valve body so debris already circulating in the pan does not contaminate the new unit, and torque the valve body bolts in the correct sequence rather than corner to corner, since uneven clamping can bind a bore that measured fine on the bench. Refill to the 8L45's roughly 7.0 liter / 7.4 quart capacity with Mobil 1 Synthetic LV ATF HP, and run the TCM's adaptive relearn drive cycle after the swap rather than driving normally, since the computer needs to relearn clutch apply timing against the new unit. If the vehicle also shows a worn clutch pack or drum from the same mileage, pair this with an 8L45 overhaul kit rather than installing a new valve body on top of worn hard parts.

Why does 2015 matter for this valve body?

2015 was the first model year GM built the 8L45 and 8L90, so this listing is for the launch-year casting - the baseline revision before any running changes made in later years.

What vehicles used the 8L45 in 2015?

GM's lighter-duty 8-speed applications such as the Colorado, Canyon, Cadillac ATS and CTS, under RPO codes M5N and M5T, as opposed to the heavier-duty 8L90 (M5U/M5X) behind V8 trucks and the Corvette.

What is this brand, and what condition is it in?

This is a TransGo-brand replacement valve body, new, built for the 2015 launch-year casting of the 8L45.

My truck won't move at all - is this the right part?

Not necessarily. Sonnax documents a separate no-move/no-pressure condition on this family caused by the chain-driven pump failing to prime, which has its own bench-prime fix rather than needing a new valve body. Rule that out first.

Should I change fluid before replacing the valve body?

Yes, for a shift-shudder complaint. GM Service Bulletin 18-NA-355 calls for a fluid change to Mobil 1 Synthetic LV ATF HP across this 8-speed family before replacing parts.

Is this the same part as the 2017 listing?

Same part family and role, but built around the 2015 launch-year casting rather than the later 2017 revision, since GM made running changes to this valve body between those years.

• 8L90 Valve Body Symptoms and Testing
• 8L90 Common Problems and Fixes