Pontiac Fiero 1984-1988 Repair Guide



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Fig. Fig. 1 Location of the automatic transaxle identification plate

All automatic transaxles have a metal identification nameplate attached to the case exterior. This nameplate will assist in the servicing and determination of replacement parts when ordering.

The Fiero equipped with a automatic transaxle uses a GM Turbo Hydra-Matic (THM 125C). This transaxle assembly is a fully automatic unit for front and mid engine GM vehicles. The THM 125C has three forward gear ranges and one reverse. The major components of the assembly consist of a 4 element hydraulic torque converter, compound planetary gear set, dual sprocket and drive link, three multiple disc clutch packs, intermediate band, valve body and vane type oil pump.


  1. P = Park position prevents the vehicle from rolling either forward or backward.
  3. R = Reverse allows the vehicle to be operated in a rearward direction.
  5. N = Neutral allow the engine to be started and operated without driving the vehicle. The engine can be restarted in the Neutral position.
  7. D = Drive position is used for all normal driving conditions. It provides three gear ratios plus converter clutch operation. Downshifts are available for safe passing.
  9. 2 = Manual second is used to provide acceleration and engine braking. This range may be selected at any vehicle speed.
  11. 1 = Manual Low is used to provide maximum engine braking. This range may also be selected at any vehicle speed.