charging pressure too high on Bobcat T300

bigboytoy · Mar 23, 2019

The code 0521 has come up but I have no symptoms. I see were it is adjusted and have read how to do it. but i don't understand why i should do anything at this point. Please help me understand what this does and what could go wrong.

willie59 · Mar 23, 2019

First thing you need to check is the charge pressure switch at the hydraulic filter, it would be the switch with three wires going to it. See if the switch is leaking fluid into the harness connector plug. If it is that will foul up the electrical information being sent to the main controller. If it's not leaking I'd consider replacing the switch anyway, it could be faulty. There's no way for you to test that switch as it's a Hall Effect sensor.

TVA · Mar 23, 2019

It would be a good idea to check the charge pressure! If the pressure indeed too high it may lead to catastrophic failure, high case drain pressure and leaking shuttle valve can cause that.

bigboytoy · Mar 24, 2019

Im curious why is a pressure switch on the input of the filter? how is that related to the charge pump?

TVA · Mar 24, 2019

I don’t know your machine specifically but many hydrostatic pumps use different filtration options, for example Takeuchi TL130 with Sauer Danfoss Series 42 uses full external filtration option, it’s not even using built in charge pump, but share the pump with pilot circuit. I would put sensor ( if it’s possible) after charge pressure relief valve. But it might be that such a port simply unavailable, or it was most suitable location for OEM.
Best thing is to know charge pressure in three locations: between pump and filter, between filter and relief valve, and after relief valve. But that’s just too much money and headache!

bigboytoy · Mar 24, 2019

willy i see no oil when i pulled the 2 pin plug ... there is a single wire plug on back of filter mount too

bigboytoy · Mar 24, 2019

after I start it takes a minute then it creates an error code. I will order a filter and change it next.

bigboytoy · Mar 24, 2019

looking at other posts i see others have problem locating charge pressure switch. Is it possible to be one of these two sensors on the fan motor

bigboytoy · Mar 24, 2019

the T300 parts manual I have shows a belt driven cooling motor .. it appears to be a hydraulic driven motor.

willie59 · Mar 24, 2019

Ahh, you have a K series T300 with the hydraulic fan, I didn't consider that. That should be the charge pressure switch on the left side of the cartridge filter in that pic. Back at the hydraulic filter in the engine compartment is the hydraulic oil temp switch (2 wires) and the oil restriction switch (1 wire). You might want to replace that cartridge filter at the hydraulic fan. And when you pull it out drop it in a clean pan with some solvent to rinse it out and check what kind and how much debris is in that filters. See if a new filter helps with your problem. I don't have a whole lot of experience with the K series cooling system, crewchief 888 knows more about that machine than I.

bigboytoy · Mar 25, 2019

a good mechanic isn't expensive hes priceless and a picture is worth a thousand words .. roger!

bigboytoy · Jun 8, 2019

well its back to the T300 charge pressure issue ...first it was code 0521 (charge pressure too High)... so I changed filter, got a new pressure switch, and replaced 5 gals of oil with iso 46 (15 w?)...then I got code 0522 (charge pressure too low... I run it for 20 hours still get code 0522 ... so I am guessing iso 45 oil is too thin... I remove 2 gallons of oil and replace with iso 100 (30 w)... I work it still it trips after start up 30-60 seconds I work it, shut down and restart... still get the code sooo.... I will wait and reassess after 20 hrs ... any ideas, its no emergency as far as I can tell there are no symptoms.

TVA · Jun 8, 2019

I would put the gauge on that circuit just to see if you indeed having charge pressure swings, or it is electrical problems.

bigboytoy · Jun 8, 2019

Ok I got 1000# gauge on order...

bigboytoy · Jul 27, 2019

I have ran it with the new oil and filter and it still comes in as 522 low charge pressure so I got a gauge and the pressure at idle is 375 which is low so I am going to pull the charge pressure adjustment plug see if it needs cleaned ... try it again ... then order some shems to raise it ... does that sound right "priceless mechanics"

TVA · Jul 27, 2019

Is your manual says 375psi is low?

willie59 · Jul 27, 2019

I don't have a manual for a T300 so I don't know what the charge pressure spec on one is.

mikebramel · Jul 27, 2019

375 is plenty

TVA · Jul 28, 2019

mikebramel said:
375 is plenty

That’s why I asked that question! For most hydrostatic transmissions I worked with it’s plenty enough! But it’s only at idle, now need to test it under load!

bigboytoy · Jul 28, 2019

manual states 410-470 is normal at high idle ... mine is 375 at low idle 390 at high idle and working the controls is goes up to 420 ... so its just a little low ... mostly with a new pressure switch I still get the code .... after I start it takes 20 seconds then the code comes in ....

charging pressure too high on Bobcat T300

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