E027

Code E27:

ISC Circuit:

DESCRIPTION:

The diagnostic test monitors the ISC throttle switch during some coast down and idle conditions with the throttle switch open and brake applied. Under these conditions, the PCM commands the ISC to retract and extend and monitors the TPS for a corresponding decrease in and increase in throttle position. If the PCM detects a decrease and increase in throttle position two times in succession, then the code will set and the service engine soon indication will be turned on.

TEST CONDITIONS:

1. Codes E21, E22, and E24 not set.
2. Vehicle in coast down condition.
3. Throttle switch open.
4. Brake applied.
5. Throttle angle 16.5° or less.
6. Engine speed greater than desired.

FAILURE CONDITIONS:

1. The above test has failed two times since the last time the throttle switch was closed.


ACTION TAKEN:

1. PCM turns "on" "SERVICE ENGINE SOON" telltale.
2. EGR is disabled.
3. When TPS is 18° or less and the brake is applied, the PCM substitutes a throttle switch closed value. When TPS is greater than 18° or if the brakes are not applied, the PCM substitutes a throttle switch open value.

NOTES ON FAULT TREE:

1. The PCM harness connector of the ISC jumper is located between the generator and cruise control servo.

2. The ISC jumper is a separate harness that connects the ISC to the PCM harness.

NOTE ON INTERMITTENTS:

Check that ISC plunger is depressed when the throttle linkage is in contact with the stop screw. Check the ISC jumper connectors, engine to dash connector and PCM connector for terminals that may not be properly crimped or backed out of their connector.