Powertrain Controls - ECM/PCM

DTC 26 Chart:

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 27 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). If the PCM detects the throttle position switch CKT 427 low when the Throttle Position (TP) sensor indicates a throttle position of 15.7 degrees or greater, DTC 26 will set.

DTC 26 WILL SET WHEN
- DTCs 21 and 22 are not set.
- TP sensor angle is 15.7 degrees or greater.
- Throttle position switch closed.
- All above conditions are present for 2 seconds or more.

ACTION TAKEN (PCM WILL DEFAULT TO)
- With a current DTC set, the PCM will illuminate the Malfunction Indicator Lamp (MIL) (Service Engine Soon).
- The PCM will disable the exhaust gas recirculation valve and assume closed throttle if brake is applied and the TP sensor indicates a throttle angle less than 18 degrees or open throttle if the brake is not applied or TP sensor indicates a throttle angle greater than 18 degrees.

DTC 26 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 or released.
2. If TP changes to "OPEN" when the ISC motor is disconnected, the fault is with the ISC motor. If TP still stays "CLOSED," check CKT 427 for a short to ground.
3. Checking if CKT 427 is shorted to ground or if the PCM is bad.

DIAGNOSTIC AIDS
An intermittent DTC 26 may be caused by any one of the following.
- A shorted TP switch.
- A short to ground in CKT 426.