Code 27 Or 28 - Gear Switch Circuits (With 3T40 Trans): Notes

Gear switches are located inside transaxle. Switches are normally closed. As vehicle speed increases, hydraulic pressure applies specific gear clutches and gear switch opens. ECM uses gear switch input signals in calculations to determine control fuel delivery and TCC operation.

Code 27 will set if mid gear 2nd switch indicates ground or closed switch for 12 seconds when vehicle is in 3rd gear or if mid gear 2nd switch circuit indicates an open when engine is first started.

Code 28 will set if high gear 3rd switch circuit indicates ground or closed switch for 10 seconds when vehicle is in 3rd gear or if high gear 3rd circuit indicates an open when engine is first started.

1. A digital volt-ohmmeter must be used in this test. A test light will not work due to low voltage supplied by ECM.
2. Checks if circuit is grounded through switch.
3. Checks for a good, properly operating switch and checks circuit within transaxle for an improper ground.