DTC 26

CODE 26, SHORTED THROTTLE SWITCH CIRCUIT

IMPORTANT: If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to "Note on Intermittents.

The ECM supplies a 12 volt signal to pin B, (circuit #427) of the idle speed control motor. When the engine is operating at idle the throttle linkage closes the throttle switch and pulls circuit #427 to 0 volts through the ground circuit of pin A, (circuit #450). When the throttle switch is closed, the ECM and idle speed control motor will precisely control the engine speed for all operating conditions.










Code 26, indicates that ECM is seeing a condition where the throttle switch is closed (indicated by the "LO" status light being on) with a throttle angle of 13 degrees or more (as displayed on engine data parameter .0.1) Possible causes of this condition are:
A. A defective throttle switch.
B. Defective wire, terminals, etc.
C. An ECM which is unable to process signals properly.
D. TPS disadjusted or binding.

1. To begin diagnosis, observe the "throttle switch" status light above the "Lo" button while in diagnostics. The light should go off upon application of the throttle. If the light does not go off, refer to the diagnostic decision tree for Code .7.2 since the throttle switch signal is remaining in the "closed" mode. If the status light goes off, then the TPS must be checked for binding or misadjustment.
2. If the sensor is free and correctly adjusted, enter diagnostics and display engine data parameter .0.1. Underthe condition of a Code 26 this "throttle angle" reading will be greater than 13 degrees 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 .0.1. With the opposite condition created a "throttle angle" reading of -10 to -7 degrees should be displayed. To create a low sensor signal, disconnect the TPS connector.

If the "throttle angle" reading is -10 to -7 degrees, circuit #476-X must be checked for an open. If the voltage between circuits #474 and #476-X is 0 volts, circuit #476-X is open. If the voltage is 5 volts, the ECM and wiring are OK. The fault must be improper mating of sensor terminals or a faulty TPS sensor.

3. If the "throttle angle" reading is -6 degrees or greater, then there is a short to voltage in the wiring harness or the ECM.

Note on Intermittents: If an intermittent Code 26 is being set, operate the vehicle while observing the "throttle switch" status light and "throttle angle" parameter .0.1 simultaneously. If the throttle switch ever fails to open upon application of the throttle, investigate that circuit for a malfunction. If the "throttle angle" ever jumps above 13 degrees with the throttle closed, investigate that circuit for a malfunction. This will help to isolate the location of the malfunction.