Hard Trouble Code E27: 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 12 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 open, ISC motor will not control idle speed because driver is controlling engine speed.

Trouble code indicates that throttle switch remained open during previous ignition cycle and has not yet closed during present ignition cycle. Possible causes are: Defective TPS, defective wiring, terminals, etc., or ECM is unable to process signals properly.

NOTE: The following step numbers refer to the numbers in the accompanying flow chart(s).

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 come on as throttle is released. If the light does not come on, refer to TROUBLE CODE "E.7.2" because throttle switch signal is remaining in open mode.
If status light comes on, exit diagnostics while in this "closed" throttle mode. Under this condition, "SERVICE NOW/SOON" light should go out and code "E27" should remain as an intermittent failure. If code "E27" remains as hard failure, replace ECM because it is not processing signal properly.