The Mitsubishi Pajero Owners Club®

[jonno89]

Hi
Over the last few months there has been a noise while depressing the foot brake and infrequently just while driving that sounds like a dry bicycle pump squeaking/adjusting under a spring load. I have investigated at the back of the foot pedal and managed to get some WD40 behind the boot that houses the rod that goes to the brake unit in the engine bay. This has not fixed the noise, I have also been told it's a power brake and has no servo like most methods of braking. It seems to be the brake unit itself. I've let a trustworthy garage i use to have a listen and he recons it's a dry cylinder/plunger type thing in the unit itself. It may just need reconditioned/refurbed. It has not effected the braking of the vehicle but it's really annoying. Seems to be worse on warmer days. Has anyone had this issue and was it a simple dismantle or fix.
Update, forgot to mention make and model
Mitsubishi shogun LWB 3.2 Diesel 2005

Thanks
J

[Google]

[assassin]

Make and model plus year would be handy?

[assassin]

If it is chirping and pumping normally it will be the mechanical overload valve and this noise comes from under the bonnet while the engine is running and if you listen to the unit you will hear it and this is a pressure sensor which you can buy and replace.

It is an HBB unit and these Hydraulic Booster Brake units are fairly simple and work by utilising a pump to pressurise brake fluid and store it in the accumulator until it is needed and when you press the brake it is needed, squeaking is not an issue in itself as most of them do it.

Get into your vehicle and pump the brake pedal about 40 times until the brake becomes hard, switch the ignition on and you should hear the pump kick in, or get someone to sit in the drivers seat with the bonnet up and put your hand on the HBB unit and get them to switch the ignition on and you should hear and feel the pump run, if the brake lights are on along with the brake buzzer it should quickly go off and if the HBB continues pumping and you hear the unit constantly chirping it is overpressurising and mechanically releasing pressure, so the unit is working correctly apart from not cutting off and this is either the brake ECU not shutting the signal to the relays off, or a weak sensor which is overloading.

Next is diagnostics and plugging in the fault code reader and this will either indicate a HBB unit fault code or an ECU fault code and you need to identify which.

If it is an ECU fault check the wiring from the ECU to the HBB unit.

If it shows the HBB unit it will show two options and generally these will be either the electric pump code 55 or the accumulator code 57and both of these are problematic.
Begin by clearing the fault code and if it will not clear it is a permanent or persistent fault and you will have to clear the fault first.

Begin with the relays and they are housed in a houging next to the HBB unit and are bolted to the offside front wing; remove the lid and pull a ralay to check it.
Two smaller pins at one end are the relay control pins and the two larger terminals are the ones which close and allow the power to flow to the motor, the two smaller control pins are closer together than the power flow pins.

Connect the power pins to a tester set to continuity and connect one of the control pins to one battery + terminal and the other pin to the other battery -  terminal and you should hear rhe relay click, this is it opening and closing, if you hear it clicking when you apply power to the control pins you know this is working and your meter across the power pins should show no resistance, if it does and the relay clicks it is either corroded or arced pins and a new relay is best.

To test your HBB motor you use any of the two larger pinsand attach a jumper wire and as you touch the other end of the jumper wire to the other large pin the motor should start running and you will clearly hear it, when it beging chirping it is the mechanical overload working and your motor and overload are working fine; it is running and generating sufficient pressure for your system.
To check your accumulator you put a jumper wire across the two larger pins and let the motor run intil it begins chirping and leave it overnight, start your engine normally and it shouldn't have any warning lights or audible buzzer meaning it is holding pressure.

[jonno89]

Thanks for the really informative reply. I look forward to trying this tomorrow. It is still doing it, but a bit quieter lately. I have learned to live with it a bit. It also does this noise when engine stopped and ignition on position 2. I have tried to plug in a friends OBD11 code reader but it does not work, now realising i need a mut2 code reader which are expensive. The ABS and anti skid lights are on now too. Brakes still brake though. Checked for defects in the ABS sensors and nothing stands out to me, all look in fair/normal condition for its age. I will let you know how i get on.

thanks
John

[assassin]

If your lights are on it is low brake pressure and usually this is the electric motor.

When you switch the ignition on the HBB unit reads the system pressure and if it is low it starts the electric motor which drives the pump which pumps high pressure into the accumulator which is a chamber with a piston and the bottom stores the pressurised fluid and above the piston is notrogen gas which is compressed by the piston being pushed up by the pressurised fluid where it stays until it is needed and you apply the brakes; being independant of the engine and powered by an electric motor means you always have brakes even though your engine dies.

Your pressure sensor is an easy swap as it just unplugs and the sensor unscrews and it is located on the front of the HBB unit under the reservoir and has a triangular plug (grey) with three wires in and you can test it easily as it is an open/closed switch and while the system has pressure it is closed and making a circuit and when the pressure drops it is open and is not making a circuit.

To test?

Take a shrt jumper wire about 6" (150mm) long and strip each end to the conductor.
Locate the relay box which is at the front of the HBB unit to the offside of the vehicle and is bolted to the OSF wing, remove any of the relays and note the pin positions.
Test at the 3 pin plug and you are looking for a closed circuit, if it is open it looks likely to be the fault.
If it is open circuit and yout brake lights are on you pressurise the circuit, to do this you leave the igntion off and put the jumper cables between the two larger terminals only, you should hear the HBB motor start up, if not then feel it and you should feel it running.
If the pump does not run it is the motor as you are powering it directly or a faulty breaker meaning the relay is not getting power, check by using a multimeter and putting one end to a good earth and probe both large pins and one should have 12 volts, if not it is the large breaker on the battery + terminal, if it has power you have confirmed the pump motor is faulty.
If the pump motor is fine and the pressure sensor is erratic it is the switch, about 2 minutes to replace, unplug it and unscrew it, screw the new one in and plug it in.

[jonno89]

Thanks again assassin. Really informative post. I checked the relays and they work fine. The unit is pressurizing okay as I hear it and the brake pedal is assisted. I discovered  by my friendly garage guy my offside front ABS sensor was defective from his fancy code reader. I have replaced this and the lights are now off. Bit of a red herring that. But now fixed PHEW. It is still over pressurizing and making that noise so I will just order a new pressure sensor and see if that sorts it. As you say, it's an easy fix to get at. I will update when I've done it.  


Regards
John