Powertrain Controls - ECM/PCM

DTC 27 Chart:

*** Test Chart Revised per TSB # 51-65-04 ***

CIRCUIT DESCRIPTION
The Throttle Position (TP) switch is part of the Idle Speed Control (ISC) motor. The PCM provides a 5 volt reference on CKT 427 to the ISC throttle position switch. If the ISC motor plunger contacts the throttle stop, the throttle position switch closes. When the throttle position switch is in the closed position, signal voltage to PCM is low (about 0 volt). When the throttle position switch is in open position, signal voltage is high (about 5 volts). The PCM monitors the throttle position switch state on vehicle coastdowns when the brake is applied. On coastdowns the PCM commands the ISC motor to retract and then monitors the Throttle Position (TP) sensor for a corresponding decrease in throttle angle. If the PCM detects a decrease in the TP sensor angle two times in succession, then the PCM knows that the ISC plunger is resting on the throttle stop and that the TP switch should be closed. If TP switch is not closed, then DTC 27 will set.

DTC 27 WILL SET WHEN
- DTCs 21, 22 and 24 are not set.
- Vehicle is in coastdown conditions with brake applied.
- TP sensor indicates throttle angle less than 12 degrees.
- TP switch input to PCM is high (open).
- Engine speed is at least 64 RPM higher than desired.
- At least 10 seconds have passed between brake applications or the last ISC motor retract command from PCM to ISC motor.

ACTION TAKEN (PCM WILL DEFAULT TO)
- With a current DTC 27 set, the PCM will illuminate the Malfunction Indicator Lamp (MIL) (Service Engine Soon).
- The PCM will disable the exhaust gas recirculation valve.

DTC 27 WILL CLEAR WHEN
The fault no longer exists.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1.Tech 1 PCM input TP should change states from "CLOSED" to "OPEN" when accelerator is depressed and released.
2. Checking if fault is on high or low side of throttle position switch.
3. Checking PCM ability to recognize signal or if CKT 251 is open.
4. Checking CKT 427 for an open.

DIAGNOSTIC AIDS
Refer to Diagnosis by Symptom. Testing and Inspection
Also see Chart C-2B Idle Speed Control (ISC) Check. Chart C-2B Idle Speed Control (ISC) Check