QuestionMy cruise control in my 2000 discovery series is not working. Is there a fuse I can check? any other suggestions. Thank you
AnswerHi Judy,
fuse 16 is the one I'd check.
For a more complete answer, I must bow in honour to Chris St-Louis for the following thread. This guy knows his stuff:
All markets have a common cruise control system. The cruise control system, when activated, regulates vehicle speed. The system consists of an electrical sub-system and a mechanical sub-system.
The electrical sub-system consists of the following components:
• Cruise control master switch (on/off switch).
• SET+ switch.
• RES switch.
• Cruise control ECU.
• Vacuum pump assembly.
• Brake pedal switch.
• Clutch pedal switch (manual gearbox only).
• SLABS ECU (speed signal).
• BCU (brake pedal switch and automatic gearbox gear selector lever position signal).
The mechanical sub-system consists of the following components:
• Pneumatic actuator.
• Vacuum pump.
The cruise control ECU controls the cruise control system. It is located on the right hand A post.
The system has diagnostic capabilities through TestBook.
WARNING: To avoid the risk of losing control of the vehicle, do not use cruise control on winding, snow covered or slippery roads, or in traffic conditions where a constant speed cannot be safely maintained. In these conditions and at any time the system is not being used, ensure the cruise control switch is OFF.
Cruise Control Master Switch
The cruise control master switch switches the system on and off. When the cruise control master switch is on, an LED within the switch illuminates. If the cruise control master switch is off, cruise control will not operate. The switch provides a 12 Volt teed to the cruise control ECU.
The cruise control master switch is located on the instrument panel near the steering column.
Input/Output
The input from the cruise control master switch to the cruise control ECU is either a 12 Volts ignition feed or an open circuit. 12 Volts indicates that the cruise control master switch is on and the system can be activated. An open circuit indicates that the cruise control master switch is off and cruise control cannot be activated.
TestBook will not communicate with the cruise control ECU if the cruise control master switch is off.
SLABS ECU
The SLABS ECU provides the road speed signal to the cruise control ECU. This is the same speed signal provided to the ECM. Cruise control will only operate between 28 - 125 mph (45 - 200 km/h) . Cruise control will not operate if a road speed signal is not present.
Input/Output
The input from the SLABS ECU to the cruise control ECU is a square wave oscillating between 0 - 12 Volts at a frequency of 8,000 pulses per mile (1.6 km) .
Cruise Control ECU
The cruise control ECU controls the cruise control system.
Most functions of the cruise control ECU are described under other components.
Input/Output
The diagnostic line for the cruise control system is between cruise control ECU and diagnostic socket.
The cruise control ECU does not generate fault codes however the following system information is available via TestBook:
• Last switch off reason, which was due to unacceptable speed input.
• Speed signal detected.
• Below minimum speed threshold.
• Current vehicle speed.
• Recorded SET road speed.
SET+/RES Switches
The cruise control system uses two steering wheel switches labelled SET+ and RES.
The SET+ switch performs the set speed, tap up and accelerator functions. The RES switch performs the resume and suspend functions.
With the cruise control master switch on and the vehicle in the cruise control operating speed range, one press of the SET+ switch stores a speed value in the cruise control ECU. If the switch is pressed and held while the vehicle is under cruise control operation, speed increases until the switch is released. At this point the cruise control ECU stores the new speed value. If the switch is tapped (held down for less than 0.5 second ) the cruise control ECU increases vehicle speed by 1 mph (1.5 km/h) .
If the RES switch is pressed while the systems is inactive (no stored values) the system will not respond. If there is a stored value in the cruise control ECU memory and the switch is pressed, the cruise control system operates and holds the vehicle at the stored road speed. If the cruise control system is active and the RES switch is depressed, the cruise control ECU deactivates cruise operation but maintains the current set speed value.
Input/Output
The input from the SET+ switch to the cruise control ECU is either 12 Volts or an open circuit.
The input from the RES switch to the cruise control ECU is either 12 Volts or an open circuit.
The following diagnostic information is available through TestBook:
• The state of operator switch SET+.
• The state of operator switch RES.
Brake Pedal Switch
The cruise control ECU has two inputs from the brake pedal switch that determine the position of the brake pedal. One input comes through the BCU and is low when the brake pedal is not pressed. The second input comes directly from the brake pedal switch. This input is high when the brake pedal is not pressed. On vehicles with a manual gearbox, the input from the clutch pedal switch to the cruise control ECU is connected in series with the direct signal from the brake pedal switch.
If the cruise control ECU receives a changed signal from either source, it deactivates cruise control, removing power to the vacuum pump and activating the vacuum control valve releasing all vacuum in the system.
The brake pedal switch also provides the signal to illuminate the brake lamps and the brake input to the SLABS ECU.
Input/Output
With the brake pedal and the clutch pedal in the rest position, the cruise control ECU receives 12 Volts .
With the brake pedal pressed, the cruise control ECU receives 0 Volts and a low voltage logic signal from the BCU.
NOTE: If the clutch pedal is pressed, 0 Volts are present at the cruise control ECU irrespective of brake pedal position.
Clutch Pedal Switch
The clutch pedal switch is a single pole normally closed switch. It is part of the 12 Volt brake pedal switch circuit to the cruise control ECU. When the clutch pedal is pressed, the cruise control ECU deactivates the cruise control system and releases system vacuum. The last set speed is retained in the cruise control ECU.
Input/Output
The cruise control ECU receives a 12 Volt signal through the normally closed contacts of the brake pedal switch and the normally closed clutch pedal switch.
Body Control Unit
On manual gearbox vehicles, the BCU provides cruise control lockout or suspend function as described under brake pedal switch.
On vehicles with automatic gearbox, the BCU monitors the status of the brake pedal switch as well as the status of the automatic gearbox gear selector lever. The BCU monitors the gear selector lever to determine which gearbox position the driver has selected. If the BCU detects that the driver has selected park, reverse or neutral, it sends a signal to the cruise control ECU which inhibits cruise operation or deactivates cruise control if it is activated.
Input/Output
If the BCU receives a brake pedal switch signal or an automatic gearbox gear selector lever position signal, the BCU sends a HIGH signal to the cruise control ECU. The cruise control ECU cancels or inhibits cruise control functions.
Vacuum Pump Assembly
The vacuum pump assembly contains three components:
• The vacuum pump.
• The vacuum control valve.
• The vacuum dump valve.
The vacuum pump provides the vacuum for the system while the two valves work in conjunction to allow the pump to increase the vacuum to the pneumatic actuator (increase vehicle speed) or release vacuum from the pneumatic actuator (decrease vehicle speed).
The vacuum control valve opens to allow the vacuum pump to increase the vacuum in the pneumatic actuator to increase vehicle speed. When the vehicle reaches the set speed, the vacuum pump control valve closes to hold vacuum in the pneumatic actuator and the vacuum pump is turned off by the cruise control ECU.
The vacuum dump valve is normally open. When cruise control is active, the cruise control ECU provides voltage to close the vacuum dump valve. If power is lost, (e.g. when the brakes or clutch are applied or cruise control is turned off at the cruise control master switch) the vacuum dump valve will immediately open and cruise control will be deactivated.
The cruise control ECU provides power for all three components within the vacuum pump assembly. The cruise control ECU provides earth control circuits for the vacuum pump and the vacuum control valve. The vacuum dump valve is permanently grounded.
Input/Output
The cruise control ECU provides both power and earth to the components within the vacuum pump assembly. Current draw at the vacuum pump assembly varies depending on components operating.
Vacuum Pump Current Draw
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.
Cruise Control Activation
Cruise control is a passive system. The driver must activate it. Switching on the cruise control master switch located on the instrument panel activates cruise control. An LED in the switch illuminates, indicating cruise control is available. The driver must accelerate the vehicle to the desired speed using the accelerator pedal. When the desired speed is reached, pressing the SET+ switch activates cruise control. Cruise control will only activate if the following conditions are met:
• Vehicle speed is between 28 - 125 mph (45 - 200 km/h) .
• The brake pedal is not pressed.
• The clutch pedal is not pressed (manual gearbox only).
• The gearbox is not in park, reverse or neutral (automatic gearbox only).
Function
The cruise control ECU receives the set signal and determines the vehicle speed provided by the SLABS ECU. The cruise control ECU activates the vacuum pump assembly to move the pneumatic actuator and the linkage to the throttle disc to maintain set road speed. It does this by controlling the vacuum to the pneumatic actuator.
Cruise Control Cancellation
Cancelling cruise control enables the driver to regain control of the vehicle speed by using the accelerator pedal.
Cruise control is cancelled if any of the following conditions occur:
• The brake pedal is pressed.
• The RES switch button is pressed.
• The clutch pedal is pressed (manual gearbox only).
• The cruise control master switch is turned off.
• The gearbox is placed in park, neutral, or reverse (automatic gearbox only).
Function
The cruise control ECU cancels cruise control operation by opening a vacuum control valve in the vacuum pump assembly. This releases the throttle linkage from the control of the pneumatic actuator and returns it to the control of the accelerator pedal.
The set speed will be stored in the cruise control ECU unless:
• The cruise control master switch is turned off.
• The ignition switch is turned off.
If cruise control is deactivated using either of the above methods, the set speed will be erased from the memory of the cruise control ECU.
Cruise Control Resume
Cruise control can be resumed at the previously set speed, provided the set speed has not been erased from the cruise control ECU memory as described above. To resume cruise control operation to the previously set speed, depress the RES switch once when the following conditions are met:
• A set speed is stored in the cruise control ECU.
• Vehicle speed is between 28 - 125 mph (45 - 200 km/h) .
• The brake pedal is not pressed.
• The clutch pedal is not pressed (manual gearbox only).
• The gearbox is not in park, reverse or neutral (automatic gearbox only).
Function
The cruise control ECU activates the vacuum pump assembly to move the pneumatic actuator. This moves the throttle to the set speed by adjusting the position of the throttle disc.
Accelerating While Cruise Control Is Active
There are three ways of increasing vehicle speed when cruise control is active:
• Temporarily increase vehicle speed (e.g. when overtaking another vehicle).
• Increase vehicle set speed in 1 mph (1.5 km/h) increments.
• Increase vehicle set speed.
To temporarily increase vehicle speed press the accelerator pedal until the desired speed is reached. When the accelerator pedal is released, the vehicle coasts back to the set speed. When it reaches the set speed, cruise control operation continues.
To increase the vehicle set speed in 1 mph (1.5 km/h) increments, tap the SET+ switch. Each tap on the switch increases vehicle speed.
To increase the vehicle set speed, press and hold the SET+ switch until the desired set speed is reached.
The vehicle set speed will increase if the following conditions are met:
• The vehicle is under cruise control operation.
• Vehicle speed is between 28 - 125 mph (45 - 200 km/h) .
• The brake pedal is not pressed.
• The clutch pedal is not pressed (manual gearbox only).
• The gearbox is not in park, reverse or neutral (automatic gearbox only).
Function
The vehicle responds as follows:
• It the driver accelerates using the accelerator pedal, vehicle speed increases overriding pneumatic actuator position. When the driver releases the accelerator pedal, the vehicle returns to the set speed.
• If the SET+ switch is tapped, the driver increases the stored speed and vehicle speed by 1 mph (1.5 km/h) per tap on the switch.
• If the driver presses and holds the SET+ switch, the vehicle speed increases until the SET+ switch is released. This becomes the new set speed for the cruise control ECU.
Switching Off Cruise Control
Switching off cruise control allows the driver to regain control of vehicle speed. It erases the set road speed from the cruise control ECU memory.
To switch off cruise control, press the cruise control master switch to the off position.
Function
When the cruise control master switch is turned off, the cruise control ECU switches off power to the vacuum pump assembly. The vacuum dump valve opens releasing the vacuum in the pneumatic actuator, returning the throttle disc to driver control via the accelerator pedal.
Cruise Control Description
The cruise control is selected from a switch located on the fascia. The cruise control operation is governed by a cruise control ECU located on the RH 'A' post behind the trim panel. Operation is controlled from two switches located on the steering wheel, a set/accelerate switch (SET+) and a resume/suspend switch (RES.).
A speed signal is supplied from the SLABS ECU to the cruise control ECU the cruise control ECU monitors the signal for use in its control logic circuits The cruise control system ECU supplies outputs to operate a vacuum pump and its internal control/dump valves
The vacuum acting within a pneumatic throttle actuator moves the actuator to the required position
Cruise suspend/resume - manual gearbox
Inputs to the cruise control ECU from a switch on the brake pedal mechanism or the clutch pedal mechanism can disengage the cruise control by interrupting a feed into the cruise control ECU The feed is used by the ECU to power the cruise control pump When the feed is interrupted the ECU logic circuits stop the operation of the cruise control pump open an internal dump valve and close an internal control valve. This action stops the actuator and suspends the cruise control function
In addition to the feed removal to the ECU when the brake pedal is pressed, a low voltage 'brakelight' signal is also sent via the Body Control Unit (BCU) to the cruise control ECU. The brakelight signal is also used by the logic circuits in the cruise control ECU to control the operation of the throttle actuator and control valves when the brake pedal has been pressed
Operation of the resume/suspend switch after a braking event, can restore the operation of the cruise control system if the vehicles speed is acceptable to the cruise control ECU
Cruise suspend/resume - automatic gearbox
A gearbox selector lever position sensor sends an input via the BCU to the cruise control ECU if the selector lever is in park neutral or reverse. An input to the cruise control ECU from a switch on the brake pedal mechanism will also disengage the cruise control by interrupting a feed to the cruise control ECU. The feed is used by the ECU to power the cruise control pump When the feed is interrupted the ECU logic circuits stop the operation of the cruise control pump open an internal dump valve and close an internal control valve. This action stops the throttle actuator and suspends the cruise control function.
In addition to the feed removal to the ECU when the brake pedal is pressed, a low voltage brakelight signal is also sent via the BCU to the cruise control ECU. The brakelight signal is also used by the logic circuits in the cruise control ECU to control the operation of the throttle actuator and control/dump valves when the brake pedal has been pressed
Operation of the resume/suspend switch after a braking event can restore the operation of the cruise control system if the vehicles speed and gearbox selector position is acceptable to the cruise control ECU.
Cruise Control Supply
Circuit supply
A feed from the battery positive terminal is connected by a R wire to the engine compartment fusebox, where it passes through fuse 16 and fusible link 8.
A feed from fuse 16 passes to the coil of the horn relay. From the coil of the horn relay, the feed is connected to the set/accel and res/suspend switches on a PO wire, via header C0291 LHD/C0286 RHD and the rotary coupler.
A feed from fusible link 8 is connected to the passenger compartment fusebox on a NW wire and from the fusebox to the ignition switch on a N wire
Ignition switch supply
With the ignition switch in position II, the feed from fusible link 8 flows from the ignition switch to the passenger compartment fusebox on a W wire The feed continues through fuse 30 in the passenger compartment fusebox and is connected by a GLG wire to the cruise control switch.
With the ignition switch in position II, a second feed from fusible link 8 flows from the ignition switch to the passenger compartment fusebox on a Y wire The feed continues through fuse 25 in the passenger compartment fusebox and is connected to the brake pedal switch by a GO wire
Cruise Control Operation
When the cruise control switch is on, the feed from fuse 30 in the passenger compartment fusebox passes through the cruise control switch contacts to provide power input to the cruise control ECU pin C0239-8 on a WY wire.
Simultaneously, the feed also passes through the cruise control switch indicator lamp which illuminates The indicator lamp is connected to earth on a black wire via header C0760 to earth header C0017 LHD/C0018 RHD. The cruise control ECU is earthed on a B wire from pin C0239-18 via header C0286 LHD/C0291 RHD to earth header C0018 LHD/C0017 RHD.
When the brake or clutch pedal or is not depressed the feed from fuse 25 in the passenger compartment fusebox flows to a pair of contacts in the brake pedal switch on a GO wire
Manual transmission
The feed passes from the contacts of the brake pedal switch and is connected to the clutch pedal switch by an OG wire. The feed passes through the closed contacts of the clutch pedal switch to a PG wire that is connected to pin C0239-1 on the cruise control ECU. This feed provides the power source to the cruise control pump via the cruise control ECU.
If either the clutch pedal or the brake pedal is depressed the respective switch contacts will be opened removing power from the cruise control ECU and disengaging cruise control. If the cruise control switch remains on the previous speed will be retained in the cruise control ECU memory.
The previous speed can be resumed by operation of the resume/suspend switch. The cruise control ECU will engage the cruise control if:
• The vehicle is traveling at over 28 mph (45 km/h)
• The cruise control switch is still on and has not been turned off
• The brake pedal is not depressed.
• The clutch pedal is not depressed.
Automatic transmission
The feed from the contacts of the brake pedal switch is connected by an OG wire to connector interface C0712-2/C0667-1. From the connector interface the feed continues on a PG wire to the cruise control ECU The feed from the brake pedal switch provides the power source to the cruise control pump via the cruise control ECU.
The cruise control ECU will engage the cruise control if:
• The vehicle is traveling at over 28 mph (45 km/h)
• The gearbox selector position is acceptable to the cruise control ECU
• The cruise control switch is still on and has not been turned off
• The brake pedal is not depressed.
Speed signal
The cruise control ECU receives a speed signal input on a KG wire via header C0290 to pin C0239-15 from pin C0504-3 on the SLABS ECU
Cruise set/accelerate
When the set/accel switch is operated the switch contacts close and connect the feed from the horn relay to cruise control ECU pin C0239-4 via the rotary coupler and an RW wire. This signal initiates the cruise control ECU to activate the cruise control pump functions providing all other parameters are correct.
Cruise resume/suspend
When the res/suspend switch is operated the switch contacts close and connect the feed from the horn relay to cruise control ECU pin C0239-2, via the rotary coupler and a UW wire. If cruise control is engaged, this signal suspends cruise control operation. If cruise control is suspended, the signal will initiate the cruise control ECU to engage cruise control at the speed retained in the ECU's memory.
Cruise control pump
The cruise control pump has three connections to the cruise control ECU One connection on a WU wire from pin C0239-11 supplies power directly to the pump. The control valve solenoid and dump valve solenoid are connected to pin C0239-17 of the cruise control ECU on a BY wire. The pump is earthed via pin C0239-7 of the cruise control ECU on a BR wire.
The dump valve solenoid is connected via header C0287 LHD/C0290 RHD on a GP wire to the contacts of the brake pedal switch. In normal operation the coil of the dump valve is earthed by the brake light circuit via the contacts of the the brake pedal switch. When the brake pedal is pressed power is supplied on the earth path of the dump valve solenoid. When the voltage on each side of the coil of the dump valve solenoid is equalised there is no voltage drop across the solenoid With no current flowing through the coil of the dump valve solenoid,
the solenoid is de-energised and the dump valve opens.
When the cruise control switch is on and vehicle speed is more than 28 mph (45 km/h) and less than 125 mph (201 km/h) the cruise control ECU supplies power to the pump and valve solenoids The earth paths for the pump and the control valve solenoid are switched as required by the cruise control ECU to set and maintain vehicle speed.
Other Body Control Unit (BCU) inputs/outputs
'Brakelight' Signal
If the brake pedal is depressed a pair of contacts in the brake pedal switch allow a feed to flow on a GP wire via header C0287 LHD/C0290 RHD to pin C0661-7 on the BCU. The BCU sends a brakelight signal output from pin C0661-16 on a GS wire to pin C0239-5 on the cruise control ECU.
The logic circuits in the cruise control ECU use this brakelight signal to lock out the cruise control. The internal logic of the ECU uses the brakelight signal to cancel cruise control by interrupting the earth path to the pump and activating the dump valve solenoid. The dump valve opens the vacuum chamber to ambient air pressure, the vacuum is dissipated and the throttle actuator no longer has an effect on the throttle position.
Gearbox inputs - automatic transmission
An Input for Park Neutral and Reverse positions are passed from the gearbox position selector on a BG wire via splice joint A31 and connectors C0668-5 C0681-5 to pin C0663-11 of the BCU.
If an input from the gearbox position selector or the brake pedal switch is received by the BCU, a brakelight signal is sent from the BCU to the cruise control ECU This signal will cancel or inhibit cruise control operation.
Gearbox inputs - manual transmission
There are no signals from the manual gearbox to the BCU. The BCU is permanently connected to earth header C0552, via a BG wire from pin C0663-11 through connectors C0668-5 and C0661-5 to splice joint A33. From splice joint A33 the earth continues on a B wire through connectors C0681-8 and C0668-8 to earth header C0552.
Diagnostic socket - all models
Diagnostic information can be retrieved on a K wire from cruise control ECU pin C0239-16, through header C0286 to the diagnostic socket The information can be retrieved using TestBook/T4 or other suitable scantool.
Hope this helps,
JohnMc
