6T70 Identification Guide

Half the 6T70 comebacks we hear about start at the parts counter, not on the bench. Somebody reads "2013 Traverse" off the work order, orders a valve body or a TEHCM by year, and bolts in a part built for the other generation. The unit may even program. Then it throws pressure switch codes, starts in the wrong gear or shifts like it has never met the engine. Identifying a 6T70 correctly takes about ten minutes and it is the cheapest insurance you will ever buy on this family.

This guide covers how to tell a 6T70 from a 6T75 and 6T80, how to separate Gen. 1 from Gen. 2 by RPO code, and how to year-date a Gen. 1 unit on the bench from its valve body and separator plates. It is built from GM's own bulletins, ATRA's 6T70 service notes and Sonnax's identification guides. Everything is listed in the Sources at the end.

Recommended 6T70 parts

Once you know the generation, order to it: the Gen. 1 or Gen. 2 master kit, and a Gen. 1 valve body for 2009-2013 units with the 1.83 ratio 3-5-R regulator valve.

6T70 Gen 1 Master Rebuild Kit with Pistons 2007-2012

$367.99View part

6T70 Transmission Master Rebuild Kit Gen 2 2013-Up

$447.99View part

6T70 Valve Body 2009-2013

$223.98View part

The 6T family in one paragraph

The 6T70, 6T75 and 6T80 are GM Hydra-Matic six-speed front-wheel-drive transaxles, with AWD versions driving a power transfer unit. They share a case family, a clutch layout (1-2-3-4, 3-5-Reverse, 4-5-6, 2-6 and Low/Reverse) and an internal transmission electro-hydraulic control module, the TEHCM, which bolts to the valve body inside the side cover. The 6T70 went in the V6 crossovers and midsize cars: Acadia, Enclave, Traverse, Outlook, Equinox, Terrain, Malibu, Impala, LaCrosse, Regal, SRX and XTS among them. The 6T75 is the heavier-duty version, mostly in the Lambda crossovers. The 6T80 is the high-output version, and in GM bulletin 18-NA-358 it shows up on the Cadillac XTS under its own RPO with its own valve body kit.

The family shares design roots with Ford's 6F50/6F55 (ATRA notes updated parts for one of the early failures came from both GM and Ford), and some aftermarket valves still cross over. Sonnax's oversized AFL/solenoid pressure regulator valve 124740-01, for example, is listed for the 6F50, 6F55, 6T70 Gen. 1 and 6T75 Gen. 1. It is a useful reminder that "fits a 6T70" is never the whole description of a part. The generation matters.

Step 1: Get the RPO code, not just the model year

Every GM transmission has a Regular Production Option code, and every transmission RPO starts with the letter M. As Sonnax's Jim Mobley writes in Transmission Digest, the codes are on the placard labeled "Service Parts Identification" in the glove box. If the sticker is missing or unreadable, check the trunk or the door jamb. If there is no placard at all, you can pull the RPO list from the VIN: ACDelco TDS has an RPO lookup by VIN (it requires an account), Mitchell 1 ProDemand lists them under Service tab, General Information, RPO codes, and parts sites such as RepairLink show VIN attributes.

Two cautions from that same article are worth taping to the wall. First, not every M code is a transmission code, and one oddball, MNK, has been used for both a five-speed Allison and a Gen. 3 6T40. Second, RPO codes are not unique to one generation or model year. The same code can repeat across years, and the same transmission and RPO in a different year or model can call for a different TEHCM part number. The RPO narrows the field. The year, model and engine finish the job.

The RPO codes you will actually see

• MH2, MH4, MH6, MY9 — the early 6T70/6T75 codes. GM bulletin 09-07-30-012F covers 2007-2009 Acadia, Aura, Outlook and G6, 2008-2009 Enclave, Equinox, Malibu, Torrent and VUE, and 2009 Traverse, all "equipped with 6T70/75 6-Speed Automatic Transmission (RPOs MH2, MH4, MH6 or MY9)." ATRA's notes list the same four codes for the 6T70/75 in the GM Z-body cars (Malibu, Aura).
• M7W and M7U — 6T70, per ATRA.
• M7V and M7X — 6T75, per ATRA. Bulletin 18-NA-358 lists M7V/M7X on 2014-2017 Enclave and Traverse and 2014-2019 Acadia, and M7U/M7W on LaCrosse, Regal, SRX, Equinox, Terrain, Impala and Malibu.
• MHM — the code 18-NA-358 lists alongside M7U, M7W and M7V on the 2014-2019 XTS, and the only one that gets a different valve body kit (24268463 instead of 24264343). That is your 6T80 flag.

Step 2: Gen. 1 or Gen. 2

This is the call that matters most for parts. ATRA's 6T70 service notes put it plainly: the 6T70 (RPO M7W or M7U) and 6T75 (RPO M7V and M7X) received a major control system update for the 2013 model year, but it was not rolled out everywhere at once. Because of parts availability, 6T70/75 applications with RPO codes other than M7W, M7U, M7V or M7X did not get the update until 2014 production. So 2013 had both:

• Gen. 1 — units without the controls update package. All 2007-2012 units, plus 2013 units on the older RPOs.
• Gen. 2 — units with the update. 2013 units on M7W, M7U, M7V or M7X, and everything from 2014 production on. The 6T80 exists only as Gen. 2.

In practice: a 2012 is Gen. 1, a 2014 is Gen. 2, and a 2013 is whatever the RPO says. Do not guess a 2013.

Why the generation is not a paperwork detail

Sonnax's warning is blunt: a module designed for Gen. 2 won't work properly in a Gen. 1 build. The TEHCM, the valve bodies, the separator plates, the solenoid dampers and the checkball all differ between generations, and Sonnax's identification guide shows each one side by side. Mobley's Transmission Digest piece opens with exactly this scenario, a 2012 Buick Regal with a strange no-shift condition and pressure switch codes, and the question of whether the right TEHCM is in it. He also warns against identifying the unit from the part number on the TEHCM you pull out, because it may already be the wrong one. He calls it Follower Syndrome: one shop installs the wrong module, the next shop reads the number off it and orders another wrong one.

The aftermarket follows the same split. Sonnax sells a Gen. 1 Zip Kit (6T70-ZIP) and a Gen. 2 Zip Kit (6T70-G2-ZIP), a Gen. 1 oversized AFL/solenoid regulator (124740-01) and a Gen. 2 actuator feed limit valve kit (124740-48K), and a Gen. 2 remanufactured valve body (GM6T70-2) that fits 2013-later units only. Order a kit without knowing the generation and you have a coin flip.

Step 3: Year-date a Gen. 1 on the bench

Gen. 1 was not one design. Sonnax's Gen. 1 6T70 & 6T75 identification chart splits it into four groups by five features. This is the table to use when the unit shows up on a pallet with no vehicle, or when the paperwork and the hardware do not agree.

The big break is 2008 to 2009, where the 3-5-R clutch regulator valve went from a 1.35 to a 1.83 ratio. Sonnax sells separate Gen. 1 reman valve bodies for each side of that line: GM6T70-1E for 2007-2008 units with the 1.35 ratio valve, and GM6T70-1L for 2009-2013 units with the 1.83 ratio valve. If a used valve body is going onto a 2008 case, check the regulator valve ratio before you believe the tag on the box.

Step 4: Read the hard parts

The case and geartrain carry their own date stamps, and ATRA's notes list the ones that trip people up during interchange:

• Converter housing support. 2007 and later models dropped one bolt from the torque converter housing area and use a 9-bolt support. The updated housing is not tapped for the missing bolt. The updated support backservices earlier units: leave out the bolt and follow the 9-bolt torque sequence.
• Lube trough. Updated for 2008 with a single retaining bolt. Later cases have only one bolt hole drilled. The new trough backservices.
• Output and reaction carriers. Updated for 2009. The output carrier bearing pocket is machined .01 in (.3 mm) deeper for a thicker sun gear bearing, and the reaction carrier sun gear bearing pocket is .009 in (.25 mm) deeper. The updated carriers backservice only if the updated bearings go in with them.
• Cooler lines. An updated design with longer snouts and modified case holes was built for 2008-and-later cases. It does not backservice into earlier cases, so a 2007 case needs 2007-style lines.
• 2-6 clutch snap ring. ATRA also flags an updated 2-6 clutch snap ring and case snap ring groove. Match the ring to the groove in front of you, not to the kit list.
• Reaction carrier and input ring gear. Parts catalogs often show these as one assembly. ATRA notes they are serviced as separate pieces, reaction carrier, input ring gear and ring gear snap ring, and leaving out the ring gear after a carrier replacement gives you a no-move and P2723.

Wave plates: the one ID check you do every time

GM's bulletin 09-07-30-012F calls for the updated 3-5-R waved plate, P/N 24254103, and recommends installing a new plate any time the transmission is disassembled for any reason. ATRA goes further and lists the new-design wave plates for every clutch to protect the planetary: 1-2-3-4 24259063, 2-6 24259816, 3-5-R 24254103, Low/Reverse 24259817. On any Gen. 1 unit you open, look at what is in there and assume the originals are going in the scrap bin. Our 6T70 no reverse guide covers what a broken 3-5-R plate does to the rest of the unit.

A ten-minute ID routine

1. Read the RPO off the Service Parts Identification placard, or pull it from the VIN.
2. Confirm the RPO against the year, model and engine. If more than one transmission RPO appears, match the engine.
3. Call the generation: 2012 and earlier = Gen. 1, 2014 and later = Gen. 2, 2013 = Gen. 2 only on M7W, M7U, M7V or M7X.
4. Order the TEHCM by VIN, not by the number on the module you removed.
5. On the bench, check the Gen. 1 year-date features (regulator valve ratio, separator plates, exhaust port, channel plate) against the table above.
6. Check the interchange traps: support bolts, lube trough, carrier bearing pockets, cooler line snouts.
7. Order the master kit, valve body and wave plates to the generation you confirmed.

FAQ

How do I tell if my 6T70 is Gen. 1 or Gen. 2?

Use the transmission RPO code and the model year. Per ATRA, 6T70 units with RPO M7W or M7U and 6T75 units with RPO M7V or M7X got the Gen. 2 controls update for 2013, while other RPOs did not get it until 2014 production. So 2012 and earlier is Gen. 1, 2014 and later is Gen. 2, and a 2013 depends on the RPO.

Where do I find the transmission RPO code on a GM vehicle?

Look for the Service Parts Identification placard in the glove box, and if it is not there check the trunk or the door jamb. Transmission RPO codes start with the letter M. If the placard is gone, the RPO list can be pulled from the VIN through ACDelco TDS, Mitchell 1 ProDemand or a VIN attribute lookup such as RepairLink.

What RPO codes are used for the 6T70, 6T75 and 6T80?

Early 2007-2009 6T70/75 applications use MH2, MH4, MH6 or MY9 per GM bulletin 09-07-30-012F. ATRA lists M7W and M7U as 6T70 and M7V and M7X as 6T75. GM bulletin 18-NA-358 lists MHM on the 2014-2019 Cadillac XTS, with its own valve body kit 24268463.

Can a Gen. 2 TEHCM be used in a Gen. 1 6T70?

No. Sonnax warns that a module designed for Gen. 2 will not work properly in a Gen. 1 build, and the valve bodies, separator plates, solenoid dampers and checkball also differ between generations. Order the TEHCM by VIN rather than by the part number on the module you removed, since that one may already be wrong.