ECM Code EO26 - Shorted Throttle Switch Circuit: Notes

TEST CONDITIONS: Code EO21 and EO22 clear. TPS position greater than 14 degrees. TPS voltage less than 4.5 volts (about 80 degrees).

FAILURE CONDITIONS: Throttle switch input to ECM grounded (throttle switch closed).

ACTION: ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel. ECM assumes closed throttle if brakes are applied or TPS position is less than or equal to 12 degrees. ECM assumes open throttle when brakes are off or TPS position is more than 12 degrees.

The throttle switch is part of ISC motor assembly. Pin "B" of ISC motor 4-pin connector is the throttle switch input to the ECM. The ECM provides a 4.5-6.0 voltage signal to pin "B" of ISC. When throttle lever contacts ISC plunger, throttle switch closes, shorting voltage signal at pin "B" to pin "A" which is a ground (closed throttle equals throttle switch input voltage low).

Code EO26 is designed to detect a throttle switch input that is always grounded and/or throttle switch never opens.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Code EO26 is set due to throttle switch input shorted to ground or ISC throttle switch inoperative. This should result in ECM input EI72 not cycling. ECM input EI72 code will be low at all times.
This step checks for TPS reading too high. TPS fault or misadjustment that results in a reading above 14 degrees at closed throttle, which will cause a false code EO26.
Checks for TPS too high due to TPS or TPS circuit.
If TPS and circuit are both okay, ECM should be checked. See CHART C1 - ECM REPLACEMENT CHECK.