DTC 27
Code 27,28 Chart:
Codes 27, 28 Wiring Diagram:
CIRCUIT DESCRIPTION:
The gear switches are located inside the transaxle. They are pressure operated switches, normally closed. The ECM supplies 12 volts through each selected circuit to the switch. In any condition other than the specific gear application, the signal line monitors low voltage, low potential. As road speed increases, hydraulic pressure applies the specific gear clutches and the gear switch opens. At this time, the ECM monitors a high, 12 volt potential, and interprets this to indicate that gear is applied. The ECM uses the gear signals to control fuel delivery (and TCC).
Code 27 will set if:
^ CKT 232 indicates ground (closed switch) for 12 seconds when vehicle is operating in 3rd gear.
^ Engine running.
^ Brake not applied.
^ No code 38.
^ CKT 232 indicates an open (drive) when the engine is first started.
Code 28 will set if:
^ CKT 438 indicates ground (closed switch) for 10 seconds when vehicle is operating in 2nd gear.
^ CKT 438 indicates an open (drive) when the engine is first started.
^ Engine running.
^ Brake not applied.
^ No code 38.
^ Codes 27, 28 do not illuminate the "Service Engine Soon" light.
TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.
1. Must use a DVM. A test light will not light due to the very low current being supplied by the ECM.
2. Checks to see if CKT is grounded through the switch.
3. Checks for a good, properly operating switch and checks CKT within transaxle for an improper ground.
DIAGNOSTIC AIDS:
^ An intermittent may be caused by a poor connection, mis-routed harness, rubbed through wire insulation, or a wire broken inside the insulation.
Check For:
^ 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.
^ Mis-routed Harness Inspect wiring harness to insure that it is not too close to high voltage wires, such as spark plug leads.
^ Damaged Harness Inspect harness for damage. If harness appears OK, "Scan" while moving related connectors and wiring harness. A change in display would indicate the intermittent fault location.