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Hard Trouble Code E26: Notes

NOTE: If this code is not displayed during second pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure.

The ECM supplies 5 volt signal to pin B (circuit No. 427) of ISC motor. When engine is operating at idle, throttle linkage closes throttle switch and pulls circuit No. 427 to 0 volts through the ground circuit of pin A (circuit No. 450). When throttle switch is closed, ECM and ISC motor will control engine speed or throttle angle for all operating conditions.

Trouble code indicates that ECM is seeing a condition where throttle switch is closed (indicated by "OFF" light on CCP panel) with a throttle angle of 13° or more (as displayed on engine data parameter P.0.1). Possible causes are: Defective TPS, defective wiring, terminals, etc., ECM is unable to process signals properly, or TPS misadjusted or binding.

NOTE: The following step numbers refer to the numbers in the accompanying flow chart(s).
  1. To begin diagnosis, clear ECM codes and observe "OFF" button on CCP panel. When a code is present, status light will represent a "failsoft" value. Therefore, it is important that any codes present are cleared before proceeding. Diagnostics should not be exited since ECM will not set a code while in diagnostic mode. Light should go off upon opening of throttle. If the light does not go off, refer to TROUBLE CODE "E.7.2" because throttle switch signal is remaining in closed mode. If status light goes off, then TPS must be checked for binding or misadjustment.
  2. If sensor is free and correctly adjusted, enter diagnostics and display engine data parameter P.0.1. Under condition of this code, reading will be greater than 13° at closed throttle. If the opposite condition (low TPS signal) can be created, then self-diagnostics can be used to detect this failure by displaying engine data parameter P.0.1. With opposite condition created, reading of B10 to B7° should be displayed. To create a low sensor signal, disconnect TPS connector. If reading is B10 to B7°, circuit No. 476A must be checked for an open. If voltage between circuit Nos. 474 and 476A is 0 volts, circuit 476A is open. If voltage is 5 volts, ECM and wiring are okay. Fault is improper mating of sensor terminals, or faulty TPS sensor.
  3. If reading is B6° or greater, then there is a short to voltage in wiring harness or ECM.
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