5.21.1 Description

The "drive by wire" throttle body controls the rate of airflow into the engine. The throttle valve position is determined by the ECM based on the airflow required to achieve the current engine torque demand. A geared direct current electric motor arrangement and a return spring control the throttle valve position, and the actual position is fed-back to the ECM by 2 potentiometer type position sensors.

The ECM controls the throttle valve position by means of a PWM and direction controlled H-bridge drive, which controls the current supplied to the motor. With no current supplied to the motor, the throttle valve will return to a 'limp-home' position, which is slightly open to allow a small amount of air through to the engine to allow it to continue running. The ECM will test the throttle valve actuation at 'key on' by quickly opening and closing the throttle valve before the driver starts the engine. Note that under 'steady state' conditions, the throttle valve will vibrate slightly due to the nature of the drive current.

There are four throttle control motor diagnostic checks: -

1. An electrical continuity check when the battery voltage is greater than 9V. A short to battery positive or ground can be detected.
2. A rationality check where a fault is detected if the difference between the actual and target position of the throttle valve is more than 10"TRIANGLE".
3. A rationality check where a fault is detected if the throttle control valve duty cycle is equal to or greater than 99%.
4. An idle speed control check where a fault is detected if the engine speed is less than the target idle speed minus 100 RPM or the engine speed is greater than the target idle speed plus 100 RPM.
   Throttle Control Motor
   
   

   Component/System	Fault Codes	Monitoring Strategy Description	Malfunction Criteria	Threshold value	Secondary Parameter	Enable Conditions	Time Required	MIL Illumination
   Throttle Control Motor	P1631	Electrical continuity	Short to battery positive or Ground	Battery positive					> 9.0V	0.150 s / continuous	two driving cycles
   	P1630	Rationality Check	Difference between actual and target position	> 10°	1.0 s / continuous
   	P1628 P1629		Throttle control duty Cycle	"LESS THAN EQUAL TO" 99%	0.5 s / continuous
   	P0505	Idle speed control check	Engine speed OR	< Target idle speed - 100 RPM > Target idle speed + 100 RPM	Engine state Vehicle speed Throttle closed for ECT	Idle 0 mph > 1.9 s 60 < ECT < 105°C	20 s / continuous
   MAF EVAP canister purge valve duty ratio EVAP canister purge functional check						< 0.61 g/rev < 7.03% Not in progress

If the above table does not include details of the following enabling conditions: - IAT, ECT, vehicle speed range, and time after engine start-up then the state of these parameters has no influence upon the execution of the monitor.