P027

DTC PO27:

ISC Motor And TP Switch Circuits:

CIRCUIT DESCRIPTION
The diagnostic test monitors the Idle Speed Control (ISC) Throttle Position (TP) switch during coast down conditions with the throttle position switch open and brake applied. At coast down, the Powertrain Control Module (PCM) commands the ISC motor to retract and monitors the TP sensor for a corresponding decrease in throttle position. If the PCM detects a decrease in throttle position sensor reading 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, P022 and P024 are not set.
2. Vehicle in coast down condition.
3. Throttle position switch open.
4. Brake applied.
5. Throttle position 12 degrees or less.
6. Engine speed at least 64 rpm greater than desired.
7. At least 10 seconds have passed between brake applications or the last ISC motor pulse from the PCM.

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

ACTION TAKEN
1. PCM turns "ON" the Malfunction Indicator Lamp (MIL) (Service Engine Soon).
2. PCM disables Exhaust Gas Recirculation (EGR).
3. Garage shift adapts are maintained at current levels.

NOTES ON FAULT TREE:
1. "LOW FAN" status light should cycle from "ON" to "OFF" to "ON" when accelerator is depressed and released.
2. Checking if fault is with the throttle position switch.
3. Checking CKT 427 for an open.
4. Checking PCM ability to recognize signal or if CKT 451 is open.

NOTE ON INTERMITTENTS:
Code P027 may be set if the Torque Converter Clutch (TCC) Brake Switch is sticking open or the accelerator and brake pedals are depressed simultaneously. Use input switch test PI71 to determine if the brake switch is functioning properly.