Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Code 28 Or 29, Gear Switch Circuits - 3.3L A Body With 4T60: Notes
TRANSAXLE
The gear switches are located inside the transaxle. Switches are normally closed. As road speed increases, hydraulic pressure applies the specific gear clutches and the gear switch opens. The ECM uses the gear switches to help determine control of fuel delivery and TCC operation. Code 28 will set if circuit No. 108 indicates ground or closed switch for 12 seconds when the vehicle is in 4th gear or if circuit No. 108 indicates an open when engine is first started. See Figure.
Code 29 will set if circuit No. 446 indicates ground or closed switch for 10 seconds when the vehicle is in 4th gear or if circuit No. 446 indicates an open when engine is first started.
- A digital volt-ohmmeter must be used in this test. A test light will not work due to the low voltage supplied by the ECM
- Checks if the circuit is grounded through the switch
- Checks for a good, properly operating switch and checks circuit within transaxle for an improper ground.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.