Code 27, 28 Or 29, Gear Switch Circuits: 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 switches to help determine control of fuel delivery and TCC operation.

Code 27 sets if Code 29 is not present, 2nd gear signal circuit indicates ground or closed switch for 10 seconds when vehicle is in 4th gear, or 2nd gear or 4th gear circuits indicate an open when engine is first started.

Code 28 sets if 3rd gear circuit indicates ground or closed switch for 10 seconds when vehicle is in 4th gear or if 3rd gear or 4th gear circuit indicates an open when engine is first started.

Code 29 sets if 4th gear circuit indicates ground or closed switch for 10 seconds when vehicle is in 4th gear (TCC locked and brake not applied) or if 4th gear circuit indicates an open when engine is first started.

NOTE: Test numbers refer to numbers on diagnostic chart.

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