Idle Speed/Throttle Actuator - Electronic: Testing and Inspection

Fig. 1 Location Of ISC:

Fig. 1 Idle Speed Control Valve:

Fig. 2 Throttle Body With ISCV:

Diagnostic Codes: P 0506, P 0507, P1508, P1509

Monitoring Procedure
Open and short circuit problems with the idle speed control (ISC) stepper motor and wiring are detected by sampling the stepper motor coils fault status lines from the Serial Output Device. Stepper motor coils are checked for open circuit after referencing, during power down; the power to the stepper motor is not removed until after this test and if a given number of consecutive faults occur on any coil, an open circuit fault is present.

Both ends of the stepper motor coils are checked for short circuit during power down referencing and if a given number of fault events occur for any coil, then a short circuit fault is present.

The closed loop test monitors the cumulative opening and closing idle speed control steps, a fault being registered when the steps exceed the limits without causing a corresponding change in airflow rate.

If these tests are not passed then a fault event has occurred. When sufficient fault events have occurred then a fault is registered. The strategy will report to the Diagnostic Status Manager (DSM) when an ISC monitoring fault is present and the DSM will then decide whether to store a fault code and illuminates the MIL Lamp.

ISC RPM Low, P 0506
During closed loop control a test monitors the cumulative opening and closing ISC steps, a fault being logged when the cumulative steps applied in either direction exceed threshold values, without having caused a corresponding in crease or decrease in airflow rate to beyond threshold values.

Threshold number of cumulative steps: 120
Minimum coolant temperature for diagnostic to operate 79 °C
Minimum engine speed for diagnostic to operate manual 485 rpm
Minimum engine speed for diagnostic to operate auto 485 rpm
Minimum engine speed for diagnostic to operate manual only 75 %

Possible Causes:
- ISC passages blocked
- ISC stepper motor jammed
- ISC stepper motor incorrectly mounted
- Air flow meter fault - output stuck
- ISC motor disconnected
- Engine not running properly - e.g, open throttle and still at idle

ISC RPM High, P 0507
During closed loop control a test monitors the cumulative opening and closing ISC steps, a fault being logged when the cumulative steps applied in either direction exceed threshold values, without having caused a corresponding increase or decrease in airflow rate to beyond threshold values.

Possible Causes:
- Base idle set too high
- ISC passages blocked
- ISC stepper motor jammed
- ISC stepper motor incorrectly mounted
- Airflow meter fault - output stuck
- ISC motor disconnected
- Air leak passed throttle

ISC Open Circuit, P1508
Open and short circuit tests check for hardware failures by monitoring the stepper motor coils fault status lines.

The open circuit test checks for open circuit stepper motor coils during power-down, after ISC power-down referencing (which enables the ECM to align the valve to a reference opening). The power to the stepper motor is not removed until after this test. During a power-down, if a given number of consecutive fault events occur for any coil, then an ISC open circuit fault is present.

The short circuit test checks both ends of the stepper motor's coils during power down referencing. During a power down, if a given number of consecutive fault events occur for any coil, then an ISC short circuit fault is present.

Possible causes:
- ISC wiring open circuit in one or more wires
- ISC stepper motor fault - open circuit coil
- ECM fault - open circuit coil drive

ISC Short Circuit, P1509
Open and short circuit tests check for hardware failures by monitoring the stepper motor coils fault status lines. The open circuit test checks for open circuit stepper motor coils during power-down, after ISC power down referencing (which enables the ECM to align the valve to a reference opening). The power to the stepper motor is not removed until after this test. During a power-down, if a given number of consecutive fault events occur for any coil, then an ISC open circuit fault is present.

The short circuit test checks both ends of the stepper motor coils during power down referencing. During a power-down, if a given number of consecutive fault events occur for any coil, then an ISC short circuit fault is present.