Engine management system - V8 (Pneumatic actuator): Description and operation

When cruise is requested, the cruise control ECU provides voltage to the vacuum pump assembly and provides a pulsed earth signal. The pulse period is dependent on the difference between the vehicle set speed and the actual road speed. Removing the earth path switches off the pump.

Several fault codes can be generated:

Fault codes 1 "Output power LOW when HIGH is expected" is flagged when Pin C0239-11 is shorted to earth.

This could be due to an external fault or an internal ECU fault and will be set if pin C0239-11 is LOW for longer than 240 milliseconds, while in cruise mode. 2 "Output power HIGH when LOW is expected" is flagged when Pin C0239-11 is shorted to battery voltage.

This could be due to an external fault or internal ECU fault and will be set if pin C0239-11 is HIGH for longer than 250 milliseconds while not in cruise mode. 3 "Output pump LOW, when High is expected" is flagged when Pin C0239-7 is shorted to earth.

This could be due to an external fault or an internal ECU fault. This fault will be set if pin C0239-11 is HIGH for longer than 7.5 milliseconds while pin C0239-7 is LOW for longer than 2.5 milliseconds while decelerating under control of cruise. 4 "Output pump HIGH, when LOW is expected" is flagged when Pin C0239-7 is shorted to battery voltage.

This could be due to an external fault or an internal ECU fault. This fault will be set if pin C0239-7 is LOW for longer than 7.5 milliseconds of the last 8 pulses when the pump is switched on while accelerating under the control of cruise. 5 Output valve LOW, when HIGH is expected is flagged when Pin C0239-7 is shorted to battery voltage.

This could be due to an external fault or an internal ECU fault and will be set if pin C0239-17 is LOW for longer than 2.5 milliseconds while pin C0239-7 is HIGH for longer than 2.5 milliseconds and pin C0239-11 is also HIGH for longer than 7.5 milliseconds, while decelerating under control of the cruise control ECU. 6 Output valve HIGH, when LOW is expected is flagged when Pin C0239-17 is shorted to battery voltage.

This could be an external fault or an internal ECU fault. The fault will be set if pin C0239-17 remains HIGH for longer than 35 milliseconds after the vacuum control valve is switched on, while accelerating under control of the cruise control ECU.

TestBook can be used to determine the fault codes present as well as the general status of the system.

Pneumatic actuator

The cruise control ECU controls the position of the throttle disc by regulating the amount of vacuum applied by the vacuum pump to the pneumatic actuator. The pneumatic actuator is an air tight bellow coupled to the pneumatic pump via a vacuum pipe. The pump evacuates the air inside the bellow and pipe, which collapses the bellow. This pulls on a cable, which moves the throttle disc to the desired position. On vehicles from 03 model year, the cruise control vacuum pump and pneumatic actuator assembly is fitted with a heat shield to protect the components from heat from the exhaust manifold.