CODE E027, E028 & E029, 2ND, 3RD & 4TH GEAR SWITCH DIAGNOSIS Oldsmobile Toronado IV

CODE E027, E028 & E029, 2ND, 3RD & 4TH GEAR SWITCH DIAGNOSIS

Gear switches are located inside the transaxle. They are pressure operated switches, that are normally closed. The ECM supplies 12 volts through each selected circuit to switch. In any condition other than the specific gear application, signal line monitors low voltage or low potential. As road speed increases, hydraulic pressure is applied to specific gear clutches, and gear switch opens. During this time, ECM monitors high 12-volt potential and interprets this to indicate that gear is applied. The ECM uses gear signals to control fuel delivery (and TCC).

Note. Test numbers refer to test numbers on diagnostic chart.

Code E027 will set under the following conditions

1. Circuit No. 581 indicates ground or closed switch when vehicle is in 4th gear operation.
2. Circuit No. 581 indicates an open (drive) when the engine is first started.

Code E028 will set under the following conditions

1. Circuit No. 108 indicates ground or closed switch when vehicle is in 4th gear operation.
2. Circuit No. 108 indicates an open (drive) when the engine is first started.

Code E029 will set under the following conditions

1. Circuit No. 446 indicates ground or closed switch when vehicle is in 4th gear operation.
2. Circuit No. 446 indicates an open (drive) when the engine is first started.

1. Digital Volt/Ohm Meter (DVOM) must be used. A test light will not light due to the very low current being supplied by the ECM.
2. Checks to see if circuit is grounded through switch.
3. Checks for a good, properly operating switch. Also checks circuit within transaxle for an improper ground.

An intermittent may be caused by a poor connection, incorrectly routed harness, rubbed through wire insulation or a wire broken inside insulation. Check for the following

1. Poor Connection, at ECM pins. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal to wire connection.
2. Misrouted Harness. Inspect wiring harness to ensure that it is not too close to high voltage wires, such as spark plug leads.
3. Damaged Harness. Inspect harness for damage. If harness appears okay, "Scan" while moving related connectors and wiring harness. A change in display would indicate the intermittent fault location.

2nd, 3rd & 4th Gear Switch Diagnosis. Scheme 150