Code 27/28 Or 29: Gear Switch Circuits (3.8L): Notes

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 control fuel delivery and TCC operation.

Code 27 will set if no Code 29 is present, circuit No. 581 indicates ground or closed switch for 10 seconds when vehicle is in 4th gear, circuit No 581 indicates an open when the engine is first started or if circuit No. 446 is open when the engine is first started.

Code 28 will set if circuit No. 108 indicates ground or closed switch for 10 seconds when the vehicle is in 4th gear, circuit No. 108 indicates an open when engine is first started or circuit No. 446 is open when the engine is first started.

Code 29 will set if circuit No. 446 indicates ground or closed switch for 10 seconds when the vehicle is in 4th gear (TCC locked and brake not applied) or if circuit No. 446 indicates an open when engine is first started.

NOTE: Test numbers refer to test numbers on diagnostic chart.

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