Automatic transmission, 3 speed (merchandising code for the THM 125C)

Years 1982–87, 1989–94 Models 10 Factory citations 20

Also described as Transmission, automatic, 3 speedTransmission, automatic 3 speedTransmission, 3 speed automaticTransmission, 3 speed automatic (merchandised order code)Automatic transmission, 3 speed (merchandising code for the THM 125)

Also documented for Buick Chevrolet GMC Oldsmobile Saturn

Documented applications

1000 — T-body (1983–1987)

1985 Single-source

matched to the unit by meaning: carwhere.com's 1985 Pontiac 1000 page lists an Automatic 3-spd, but prints no RPO code; the 1984 kit page prints the code as MX), which is not an accepted reading, and the 1986 kit page has no readable model year, so those years are left out although carwhere.com also lists an automatic for them; shared T-body code; cited from the Chevrolet Chevette kit

GM Heritage factory kit — 1985 Chevrolet Chevette, p.30.

6000 — A-body (1982–1991)

1985, 1989 Single-source

the ordering code for the unit MD9 names; 1986–1988 are left out because those kit pages print MXT or MXIT; matched to the unit by meaning: Wikipedia names the THM 125C on the 6000 but prints no code; shared A-body code; cited from the Chevrolet Celebrity kits

GM Heritage factory kit — 1985 Chevrolet Celebrity, p.43.
GM Heritage factory kit — 1989 Chevrolet Celebrity, p.10.

Fiero (1984–1988)

1987 Confirmed

merchandised order code for the unit the OSG calls MD9; 1987 from conceptcarz's 1987 list; the OSG gives no year

Firebird — Third generation (1982–1992)

1982 Factory-verified

Wikipedia pairs the TH-200C 3 speed automatic with the LU5; Firebird years: Wikipedia 1982; thirdgen.org powertrain tables 1982; shared F-body code; cited from the Camaro kits

GM Heritage factory kit — 1982 Chevrolet Camaro, p.30.

Grand Prix — G-body (1983–1987)

1983–1987 Single-source

the Grand Prix sources name a 3 speed Turbo Hydra-Matic (Wikipedia's infobox for the generation, the conceptcarz 1985 specifications, Wikipedia's 1986 section with the LB4, and Eighties Cars as the 1987 standard transmission) but print no code, so the code is matched by its meaning; shared G-body code; cited from the Chevrolet El Camino kit (1983) and the Chevrolet Monte Carlo kit (1984–1987)

GM Heritage factory kit — 1983 Chevrolet El Camino, p.5.
GM Heritage factory kit — 1984 Chevrolet Monte Carlo, p.33.
GM Heritage factory kit — 1985 Chevrolet Monte Carlo, p.30.
GM Heritage factory kit — 1986 Chevrolet Monte Carlo, p.32.
GM Heritage factory kit — 1987 Chevrolet Monte Carlo, p.40.

Grand Prix — W-body (1988–1996)

1991, 1993 Single-source

matched to the unit by meaning: Wikipedia's Grand Prix infobox gives the generation a 3 speed automatic and its 1990 section pairs it with the Quad 4 in the LE sedan, and the W-Body Page says the 3 speed automatic was dropped for 1994, but neither prints a code; 1990 and 1992 are left out because no listed kit page of those years prints the code; the merged lumina-gen1 doc reads MX1 as Transmission, 3 speed automatic; shared W-body code; cited from the Chevrolet Lumina kit

GM Heritage factory kit — 1991 Chevrolet Lumina, p.18.
GM Heritage factory kit — 1993 Chevrolet Lumina, p.16.

Phoenix — X-body (1983–1984)

1984 Single-source

matched to the unit by meaning: Wikipedia's Phoenix article names the 3 speed Turbo-Hydramatic 125 automatic in its infobox but prints no code; the page prints MXI (letter I); 1983 is left out because no listed kit page heads the code that year; shared X-body code; cited from the Chevrolet Citation kit

GM Heritage factory kit — 1984 Chevrolet Citation, p.34.

J2000 / Sunbird — J-body (1982–1987)

1984, 1986–1987 Single-source

matched to the unit by meaning: Wikipedia's Sunbird article names the 3 speed Turbo-Hydramatic 125C automatic in its infobox, but prints no code; the 1986 page prints MXI (letter I); 1985 is left out because the kit's option line is cut off after MX, and 1982–1983 because the brief lists no kit page of those years; shared J-body code; cited from the Chevrolet Cavalier kit

GM Heritage factory kit — 1984 Chevrolet Cavalier, p.11.
GM Heritage factory kit — 1986 Chevrolet Cavalier, p.37.
GM Heritage factory kit — 1987 Chevrolet Cavalier, p.37.

Sunbird — J-body (1988–1994)

1989, 1991–1992, 1994 Single-source

matched to the unit by meaning: Wikipedia's Sunbird article gives this generation the 3 speed Turbo-Hydramatic 125C but prints no code; 1988, 1990 and 1993 are left out because no listed kit page of those years prints the code; shared J-body code; cited from the Chevrolet Cavalier kit

GM Heritage factory kit — 1989 Chevrolet Cavalier, p.12.
GM Heritage factory kit — 1991 Chevrolet Cavalier, p.15.
GM Heritage factory kit — 1992 Chevrolet Cavalier, p.15.
GM Heritage factory kit — 1994 Chevrolet Cavalier, p.10.

Trans Sport — U-body / GMT199 (1990–1996)

1990 Single-source

with the LG6; the 1990 dealer specifications powertrains page (model year 1990, dated September 1989) names the THM 125 3 speed automatic and prints its RPO code as MXI; matched to the unit by meaning: Wikipedia's Trans Sport article names a 3 speed (3T40) automatic, the sole transmission at launch, but prints no code; 1991 is left out because the 1991 dealer specifications page (p.5), which gives MX1 for the THM 3T40, prints its model-year heading as 1951 (OCR) and only a January 1991 issue date, so its model year is unreadable; the MVMA pages give the 3 speed automatic as MD9 (see MD9); shared U-body code; cited from the Chevrolet Lumina APV kit

GM Heritage factory kit — 1990 Chevrolet LuminaAPV, p.6.

This page aggregates every documented appearance of MX1 in the Pontiac reference. Confidence and citations are shown per application — the same code can be better documented in one year than another.