Hi guys, I have a volvo L120F (SN# VCEL120FC00024676) that is constantly showing the "brake system failure warning" This is the first time i have been to this machine so i have minimal history on it and the customer also has minimal history due to staff changes and lack of record keeping. The unit has 24000 hours. Using a previous thread for information on here i have done the below initial testing all using a gauge directly into the accumulator stack. - Im seeing 2050 psi cut out pressure - Apply the brakes and it drops down to 1850 psi and the returns instantly to 2050 psi - Tilted the bucket to relief and the pressure goes to around 2250 psi and the warning goes away as the sensor sees the correct cut out - Apply the brakes thereafter and the same conditions as above re-apply - Turn the machine off and apply the brakes can get at least 6-7 applications before the gauge reads 1400 psi so i believe the accumulators are in good shape - I have adjusted the Pb reducing valve and the cut out pressure doesn't change but when bucket is tilted to relief the pressure rises as the valve is adjusted so i believe the pump is in good condition - Other things to note the fan is not spinning at normal RPM, i cant see the actual RPM in the dash in the service screen after holding key 8, or is there another trick to enter a further service mode? - Unit has a quick hitch bucket and a hydraulic park brake. - Trans oil is not gaining oil and hydraulics don't seem to be loosing any Where do i head next? Any help would be greatly appreciated
Key on, engine off, press and hold the wrench button till it says enter service mode. Press the enter key. When you see the wrench symbol in the bottom of the screen, you're in. Press the axle button. You should see brake pressure. Observe the pressure displayed against what your gauge shows. Curling bucket over relief shows max brake charging pressure. You want to be around 2400. This pressure is adjusted by the pressure reducing valve. Cut-in/ cut-out pressure is dictated by the sensor. Very often, the cut-out pressure is so close to max brake charging that the relief unloads before the brake charging is satisfied. If it stays in "charge " for more than 30 seconds, it trips "brake charging failure. "
FWF thanks when i go back to the machine in a couple of days ill check the screen reading vs the gauge reading. ive been able to set the max charging pressure without issue i wound it up to 2800 psi to check that the pump was making good pressure but the fault remained the same, but the cut out pressure hasnt reached 2200 psi. Possible sensor failure if its reading inconsistent to the gauge/ Anything else to look for/ Appreciate it
Marking. Good information and thanks.
In service after reaching max brake pressure.Btw 2800 is really pushing it , the park brake piston will not like that. Press the engine button scroll down to max fan speed. Turn it on. With brake charging satisfied, at full throttle fan speed should be close to 1800. I'll have to look up actual spec. Based on what you've reported, you're either looking at a faulty sensor (common) or a tired pump. (Not uncommon for those hours) good luck
Max fan 1700 , base speed 400. Brake charging: Cut in 1813 Cut out 2100 Max 2430.
Hi lads, Finally made it back out to this unit, i found that the front diff was slowly overfilling about 20 ltrs every couple of days so i've re-sealed both front brake pistons, luckily i did as one of the piston return springs wasn't seated correctly and was running hard agains the brake disc filling the planetary with metal. put it all back together but unfortunately the same conditions exist. still not achieving the 2100 psi cut out. Note fan speed is only 380 RPM at idle and max it reaches is 800 rpm even when the bucket tilt has been stalled and brake pressure is at the 2400 max pressure. Next test for me is to check the case drain for the fan motor as i want to ensure that isn't pulling the oil away from the pump and then i guess the only thing left is pump 3 being tired? Is there a definitive test to prove the pump is not achieving capacity? I see in the manual that at the bottom of the valve block where the reducing valve is located is a pump 3 test port but i cant find any information the manual as to what pressures i should be observing? Also to note the charge air over temp fault is now present which i assume is the fact the fan is not running to capacity and the exhaust manifold has a horrendous leak which is also on the to do list. thanks again
Cap the hose to the front axle diff lock solenoid. Have had issues with that valve leaking internally to tank. Is your parking brake a dry disc and caliper or is it a wet brake inside the trans?
Either run the fan test in the display or disconnect the coolant temp sensor and record the fan speed. To me it sounds more like you have an issue with P3.
ok will do, the park brake is a wet brake in the trans. the trans is not gaining any oil
Parking brake solenoid valve is a vickers valve just like the diff-lock. Either one can leak to tank. But that would usually result in rapid cycling vs inability to satisfy brake charging. I think Ben is correct in P3 may have just gave up after having been forced to work so hard with jacked up pressure reducing valve.
will try this also thanks
yeah im thinking the same, i only ran the reducing valve up at higher pressure for one test cycle i made sure it was only set to the 2400 max prior to putting it back to work. but i did have to adjust it when i first got to the machine as it wasnt achieving the max at stall. is there a p3 test as such? to confirm
Fan test for flow and brake charging for pressure. You're failing on both. Not a good sign. Make sure max brake charging is satisfied prior to performing fan speed test. If brake charging is demanded, the central valve will divert P3 oil to brake, away from fan. Good luck
***** Update ***** Really appreciate all the great information you guys have provided which has ultimately led me to find the fault. Carried out all tests, capped of the quick hitch and park brake with no changes to cut out pressure. Ran the p3 fan test and was 500 psi low for the max working pressure. As per manual i went to adjust this to find only 1/4 of a turn left of adjustment which raised the max working pressure by 100 psi and that was enough to satisfy the brakes and cooling fan for now. New pump on its way. Did the exhaust manifold repair and the unit is now back and working happily. Low and behold whilst on site the second unit exact same loader but with only 15,000 hrs started faulting with engine overtemp. Found fan to not be running at required RPM. Therefore i carried out all the exact same testing but found nothing out of sorts, brake cut out satisfied with 2200 psi, max system pressure when tilt stalled 2450 psi, accumulators not dropping beyond the spec in the manual when engine off and brakes applied. Capped the park brake and the quick hitch no change. Carried out the fan test, fan runs perfectly, carried out p3 pump test max pressure at spec 3090 psi. pressure on test gauge is the same as the computer so brake system sensor is ok. Only thing i have noticed that seems off is that the brake system pressure once it reaches cut out drops rather quickly without any brake application. And once the machine is turned off it continues to drop. I looked at the connections on the PWM2601 cooling fan control solenoid and they were soaked in oil internally on the plug after cleaning no difference was found. Tested voltage to the PWM2601 and found when the brake charge is satisfied 22 volts, when the fan test is activated 28 volts What am i missing? I assume i should be seeing the same voltage when brakes are satisfied vs when the fan test is on? What could the reason for v-ecm to not be sending the required voltage? thanks again
First thing. Follow hose from central valve to accumulator manifold. Remove the hose then remove the fitting from the manifold. The fitting is a one way check valve. If accumulator pressure is dropping, that's the first place to go. If the brake charging is constantly shifting between fan and brake charging, the radiator can't properly shed heat. See if that check valve is flat or blown through. I've seen both. Good luck
Will do, do you believe the voltage supply im seeing is a secondary factor to the pressure dropping?
Voltage could be correct, what's important is the mA. The voltage should be somewhat steady, it's the mA, in addition to that, you're looking at dwell or duty cycle. PWM valves are not to be confused with solenoids. One is infinitely adjustable while the other is on or off. PWM are modulated in that the voltage is there but it's turned on and off hundreds of times a second. If you break into the circuit in series you can monitor the mA, if you hook an oscilloscope in parallel you can see the frequency. If you're seeing a change in output based on changing voltage or mA odds are you're good.
From your description PWM2601 is working as it should and not a problem. Like @funwithfuel said your issue is likely the check valve in the fitting on the accumulator block. The only other thing would be very weak accumulators or a possible leak in the brake valve but less likely.