Greetings. I have a 1998 Bobcat 873 that has an intermittent problem with the lift arms and bucket tilt. The machine will be working just fine and then the green LED next to the Lock symbol on the Auxiliary Hydraulics For Attachment Operation panel in upper right will begin to flash repeatedly. Once this happens, the engine will 'bear down' as though there is an extra load on it. And then no matter which way I press the foot pedal for the lift arms they go UP. Nothing I do will lower them. Press for up, they go up. Press for down, they still go up. Same with bucket tilt. Press pedal for tilt down, it goes down. Press pedal for tilt up, it still goes down. Light still flashing continuously with no pattern to it. Steady flash. Engine still sounds like it is under load. Loader drives forward and reverse as it should. I have shut the machine off and come back to it hours later and still doing same thing. Typically if it sits overnight it will be cleared and working properly the next day. Some days it does it after 2 minutes, some days I can use it for an hour without experiencing it. I have some mechanical abilities and can possibly run some tests of components that are suggested. I have searched and searched online to find others with this same scenario and have had no luck. Whether I get it figured out with your help or I need to bring it in to have a shop do it, any and all help in finding the solution faster would be appreciated.Also, ALL lights on BICS panel are ON steady green.
Hi It sounds like your auxiliary hydraulics is activating all the time. Here are some possible causes relating to the flashing light • Wires Disconnected • Wires Shorted • Wires Cut • Solenoid failed. Perform solenoid coil test. • PWM module failed. When you are sitting in the machine, take a look at your right hand joystick lever. It may have a trigger like switch at the front of the joystick. See if you can check this switch that it is not jammed and possibly stuck on all the time. In the meantime you may be able to remove and disconnect the solenoids so that you can continue to use the lift and tilt operations until you get the electrical circuit checked out. Just note that electrical issues especially with solenoids can have the potential to start a fire. You will need to lift the cab and the solenoids will be located on the top of the control valve on the right hand side of the machine. Hopefully the attached pic may help. Kind regards
Thank you for the reply with possible solutions. I will look into it this evening and report back. Much appreciated.
So...I located the two solenoids in the pic you posted. BTW neither solenoid had a nut on the top. How important are those nuts? With multimeter set to 2k ohms, both solenoids read 023 when touching the two contacts in plug. I looked at the trigger switch on right joystick and it was definitely sticky. I sprayed a little lubricant into the trigger and it freed itself up some but does not feel as free as I think it probably should be. If you pull the trigger and release, it goes back to it's original position but seems like it could go a little more maybe. if you push on the top of the trigger it goes in a bit farther but I'm not sure where exactly 'neutral' is on the trigger. After trying these things, symptom is still there. If that trigger switch is presenting as on steady, would I be getting the symptom I have? Also, is it possible to disconnect the wire/s related to that switch down the line somewhere to see if that changes things? What exactly is the PWM module and how can I test it?
Did you try disconnecting the solenoids that are missing the nuts and running the machine as a test. Those solenoids can be sent a Pulse Width Modulated signal to proportionally control the auxiliary function or they can be set to on/off which is what the trigger switch does. Testing this signal would require an oscilloscope. Their could be a possibility that you may have 2 faults, electrical and mechanical, jammed solenoid or control valve spool.
Man do I appreciate the help you are offering on this. So... I disconnected both solenoids and swapped them. Plugged them in and no change. Then I swapped them back and narrowed it down to this: when the front one is disconnected the LED by the lock symbol continues to flash, BUT the engine does not sound like it has the 'bearing down' load on it AND the lift arms and tilt work as they should. I used it for 30 minutes to grade the driveway and still working properly with exception of blinking light. Plug it back in and goes back to bearing down load and tilt and lift only work one way. What's next? Something wacky under solenoid?
sounds like the solenoid is getting a command voltage signal when it shouldn't be. If your machine has a PWM module then it should be on the left control lever side of the machine bolted to the main frame. It will look similar to the BICS module but most likely will not have any indication LEDS. See if you can find the connectors for each joystick handle and disconnect them one handle at a time and test to see if the fault stops like you did with the solenoid test. If you lift the cab and follow the wire loom that comes out of the base of each control handle, then it should break out into 2 connectors for each handle. the 2 pin connector is the trigger switch and the 3 pin is the pwm thumb paddle switch ( if you have this option fitted) I will gather some info up in the next couple of days and send to you to help with the wiring layout and testing, if possible can you give a serial number of the machine to help with this?. I would think at this stage that one of the switches or harness wires on one of the handles maybe faulty.
Thank you. Where the wires come out of the joystick there is a plug with 5 wires. I unplugged it and the two LEDs on the Auxiliary Hydraulic panel began to flash alternately...top, bottom, top, bottom. I plugged them back in and it went back to the bottom one flashing. So I followed those 5 wires and they appear to go over to this PWM module that you are talking about.That thing is tucked up underneath there on the left side pretty good. I can feel there are several plugs but can not see which ones are with these 5 wires. I can see from the outside of the machine that there are 4 bolts that hold that module in there. I can feel the two rearmost nuts underneath there but can not reach the front two. Did some stretching today at work in hopes of being able to reach farther in there tonight to get the front ones off and be able to access the plugs on it. It is a 98 F series. VIN is 514122623
Here is some manual information to help you with testing the harness wires. See if you can test the wires to the switches in the joysticks, in particular the right joystick. The file was to large send so I have split it into 6 parts which, fingers crossed, will work.
I received the file. I will dig into it on Saturday and report back! Thank you!
I now own this machine. I have cleaned the grounds and unplugged and plugged the harness connections of the PWM back in. Still same issues. I tried simply disconnecting the RH propel arm harness (thinking the switches in this arm were bad causing the circuit to be closed when not commanded to be) and that did not solve the problem either.
I'd start tracing how it's signaling... I'd guess it's in the control. My S250 got were the auxiliary would act up, either not work or not stop, randomly stop. A new joystick/control (whatever it's called) fixed it.