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Hope you all can help or should I just take to the dealer?
While I've been working out-of-country for the summer, my wife took the 99 Discovery II for a drive, she had the cruise on and was working fine until she started coming down off of a steep hill. She hit the brake to slow down, but the cruise control wouldn't release. It stayed engaged, she had to fight the cruise control to get the speed to slow down, pedal almost to the floor and the car still wouldn't stop. Luckily, after the third hill the road leveled off with a slight incline and she was able to get to the side, but still couldn't get it to stop. She put it into neutral and then park. She said she was too panicked to find the cruise control & turn it off. She had it towed to a local mechanic (not Land Rover) but he could not find anything and could not get it to reproduce.
Now that I'm home, I've been driving it for a few days and I finally had it happen to me.
I was on the freeway, started to come up to my exit, hit brake to disengage CC, took my foot off the brake and it started to speed up again. It did this a few times, tapped brake to see if that worked, no joy. Then I turned off the power switch on dash. Still kept speeding up. I cycled the switch to see if that worked, no luck. I hit the gas to see if that had any effect, nothing. I finally had to put it in neutral, and the engine started to rev, I punched the gas and then it finally kicked off and I could slow down. Any ideas?
I believe that there are two switches on the brake pedal actuator, one operates the actual brake lights and the other signals the cruise control. Don't use cruise until checked / replaced. Guess you could pull fuse 25 below to make sure it does not get activated by "accident."
From the RAVE: (under cruise control)
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.
And I mis-quoted the obvious, there is one brake switch, it just has single pole double throw action (three wires) - so when not pressing the brake pedal it sends voltage to the cruise system, when pressed that voltage is sent to the brake lights instead. It's S215 on the drawings, appears for both brake and cruise diagrams. Less than $30 usually.
really appreciate the help here guys and I will look at replacing this switch, but I'm curious, if it is the switch why when I killed power on the dash did it not kill the system. Does killing power not release the vacuum on the system?
Like a lot of modules, the cruise ECU has power most of the time. Pressing the dash switch is a command to use/not use cruise control. But the RAVE electrical wiring diagram shows that the power from the brake switch applies to the cruise control pump dump valve input directly. So if bad switch, valve to dump vacuum is not triggered.
Now, if it is not the cheap brake switch, then the cruise control pump could be bad. Below is more info and places to meter, voltages to expect.
Note: About now, she-who-must-be-obeyed could be planning for you to dispose of this truck.
Description:
Pump-Cruise control - LHD
Location: Rear RH side of engine compartment
From the RAVE:
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 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 (45km/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.
really appreciate the help here guys and I will look at replacing this switch, but I'm curious, if it is the switch why when I killed power on the dash did it not kill the system. Does killing power not release the vacuum on the system?
your switch is electronic not vacuum actuated like disco one.
but its possible the cable itself or the throttle is sticking.
clean the throttle and throw a brake switch in to be on the safe side. We have issues with the brake switch. if it is updated it will have a large white and blue switch with a jumper harness on it.
But have had issues with random throttle sticking even in spring from sticking throttle plates.
__________________
"If you think it's expensive to hire a professional to do the job, wait until you hire an amateur." Red Adair
Land Rover technician Got a problem just ask. If you are a fellow LR tech then I would like to hear from you.
really appreciate the help here guys and I will look at replacing this switch, but I'm curious, if it is the switch why when I killed power on the dash did it not kill the system. Does killing power not release the vacuum on the system?
Shutting off the main power supply (the on/off switch on the dash) turns off the cruise control computer which will turn off the cruise.
HOWEVER, you did that and the truck still would not slow down, this is why I asked what the temp has been where you live.
There is a heater on the throttle body, if it has been by-passed (common) and it is chilly and humid where you live your throttle plate can freeze and you cannot slow down because the frozen throttle plate is just like holding your foot on the gas pedal.
This is also why Rovin4life has said that you need to check the throttle body for a sticky throttle cable or a weak spring.
There is a spring that pulls the throttle plate closed when you let your foot off the gas pedal, when you press the gas pedal you are pulling against this spring.
If the spring gets weak the throttle plate may not close properly and it will be just like having your foot on the gas pedal.
If there is dirt inside the throttle cable housing this can also cause the throttle to not close properly.
Open the hood, have your wife (with the engine off) press the gas pedal to the floor and release while you look for what is moving, clean those moving parts with carb or brake cleaner.
Then lube them with a silicone spray.
Cruise Control would not release, unable to brake
