P027

Code PO27:

ISC Motor Circuit:

DESCRIPTION:
The diagnostic test monitors the Idle Speed Control (ISC) throttle position switch during some coast down and idle conditions with the throttle position switch open and brake applied. Under these conditions, the PCM commands the ISC to retract and monitors the TP sensor for a corresponding decrease in throttle position. If the PCM detects a decrease in throttle position two times in succession, then the PCM knows the throttle is resting on the ISC plunger and the throttle position switch should be closed and it sets Code P027.


TEST CONDITIONS:
1. Codes P021, PO22 and P024 not set.

2. Vehicle in coast down condition.

3. Throttle position switch open.

4. Brake applied.

5. Throttle angle 16.5 degrees or less.

6. Engine speed at least 64 RPM greater than desired.

7. At least 4 seconds have passed between brake applications or the last ISC motor pulse from the PCM.


FAILURE CONDITIONS:
1. The PCM retracts the ISC motor and sees a corresponding decrease in throttle angle twice.


ACTION TAKEN:
1. PCM turns 'ON' the 'SERVICE ENGINE SOON' MIL.

2. PCM disables EGR.


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.


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