Body control unit (Cruise control): Description and operation

Cruise control

The Neutral/ Reverse/ Park/ Brake selected output is used by the cruise control system. The BCU checks for the following inputs: l Ignition on. l Gearbox state. l Brake switch activated.

For vehicles with manual transmission, Neutral/ Reverse/ Park/ Brake selected output is on if the ignition is on and brake switch activated is on. Otherwise, the Neutral/ Reverse/ Park/ Brake selected output is off.

For vehicles with automatic transmission, the Neutral/ Reverse/ Park/ Brake selected output is on if the ignition is on and brake switch activated is on, or if the ignition is on and 'gearbox state' is in Neutral, Park or Reverse. Otherwise Neutral/ Reverse/ Park/ Brake selected output is off.

Shift interlock (where fitted)

On automatic gearbox models, the BCU and IDM combine to operate a shift interlock solenoid, so that the gear selector lever can only be moved when certain logical conditions have been satisfied. Operation of the interlock may be affected, if the battery becomes discharged. AUTOMATIC GEARBOX - ZF4HP22 - 24, DESCRIPTION AND OPERATION, Description.

When the gear selector lever is in the Park position and the ignition is off, an interlock solenoid is de-energised, locking the gear selector lever in the Park position.

The gear selector lever can only be moved from the Park position when the ignition is switched on and the brake pedal is depressed. When these conditions are satisfied, the brake pedal switch signal is received by the BCU which then signals the IDM to energise the interlock relay. When the interlock relay is energised, the interlock solenoid is operated, unlocking the gear selector lever.

When the brake pedal is released, the feed to the BCU is removed and the shift interlock solenoid is de-energised. The locking mechanism controlled by the solenoid will lock the gear selector lever once it is returned to the Park position.

The shift interlock option can be programmed in one of three states dependent on market/ customer requirements, these are: l Option 1– not fitted. l Option 2 – normal operation. l Option 3 – inhibit transfer box.

The BCU checks the status of the following inputs to determine the logic action for employing the shift interlock solenoid: l Brake switch activated. l Ignition state. l Gearbox state.

In the event of a communications link failure, the shift interlock solenoid enable is switched on for 1 minute every time the ignition is switched on and switched off when the ignition is turned off.

Ignition interlock (where fitted)

On automatic gearbox models, when the ignition key is inserted in the ignition switch, the ignition key-in switch contacts close to supply a signal to the BCU to indicate the presence of the key in the switch and provide a supply feed to the ignition interlock solenoid. If the gear selector lever is in a position other than Park, or the 'transfer box neutral selected' is on, the BCU will supply an earth path to complete the ignition interlock circuit and cause the interlock solenoid to be engaged. With the interlock solenoid engaged, removal of the ignition key is prevented. The BCU will open the circuit, to allow removal of the ignition key, only when the gear selector lever is in the Park position and the transfer box is in either high or low range.