E026

TEST CONDITIONS
1. Codes EO21 and EO22 not set;
2. TPS equal to or greater than 20 degrees;
3. TPS less than or equal to 75 degrees.

FAILURE CONDITIONS
Throttle switch input to the ECM grounded (Throttle switch closed) for 1.5 seconds.

ACTION TAKEN
1. ECM turns on "Engine Control System Fault" telltale;
2. ECM commands BCM to display "Service Soon" message on Driver Information Center (DIC);
3. EGR is disabled;
4. ECM assumes the throttle switch is closed if brake is applied and TPS is less than or equal to 18 degrees;
5 ECM assumes the throttle switch is open if brake is not applied or if TPS is greater than 18 degrees.

DESCRIPTION
The throttle switch is part of the ISC motor assembly. The ECM provides a 5 volt reference on CKT 427 to Pin B of the ISC weather pack connection. When the throttle contacts the ISC plunger, the throttle switch closes, connecting Pin B to ground at Pin A. When the throttle switch is closed, throttle switch input voltage is low (ground). Code EO26 sets when the ECM sees a TPS signal greater than 20 degrees (accelerator being applied) but the throttle switch remains closed.

Possible causes of Code EO26 are:
1. Throttle switch circuit shorted to ground (CKT 427);
2. Faulty throttle switch.

Notes on Fault Tree
1. Checking for throttle switch status light to cycle. If status light does not cycle, follow ECM input EI72 trouble tree.
2. Checking for TPS reading too high or a TPS fault or misadjustment that results in a reading above 20 degrees at closed throttle that will cause a false Code EO26.
3. Checking for TPS too high due to TPS or TPS circuit.
4. If TPS and TPS circuit are OK, the ECM should be checked per Chart C-1. Chart C-1 Vehicle Will Not Enter Diagnostics

Notes on Fault Tree
Select ECM input EI72. Manipulate ISC connector, ISC wiring, and ECM connector and observe status of input. If the the throttle switch state change momentarily, an "X" will be recorded. Check for intermittent opens and shorts in the wiring. Manipulate TPS connector and wiring while observing ECM data ED01 and watch for TPS value to go above 20 degrees at closed throttle.