Hey guys, I have an issue with the two speed travel function on my excavator, Cat 311B, s/n 8GR00401. The travel selector button in the cab does not change the travel speed range (although it cycles between low and high range on the indicator panel). Although the indicator light defaults to low range when I start the machine it feels like it’s stuck in high range. I asked for a local heavy equipment mechanic to diagnose and fix this issue but he’s scheduled out several weeks at least. Note that I bought this machine early this year and the two speed function has never worked. Can anyone give me some direction in troubleshooting this issue? Thank you!
Are you sure you are stuck in rabbit mode? When traveling and you use a boom function or cab movement does it kick down into a slower speed?
That’s a good question, I’ll try using another function while tracking and see if it changes anything. I am not 100% sure it’s stuck in high speed as I have nothing to compare it to. But it seems to me that it travels too fast for low speed. I had the machine inspected prior to purchase by a Cat dealer and their tech told me it was stuck in high speed. Thanks for the pointer, I’ll report back.
I'd nearly bet money on the pressure switch when in rabbit it is use to knock it in to low when turning aka when the pressure gets high
Any test on this pressure switch other than replacing it? I’ve also seen references to a solenoid valve that can act up. Can you post a picture or explanation of where the pressure switch or the travel speed solenoid are located? Thanks!
Travel auto downshift (to turtle from rabbit, when travel encounters steep grade or heavy mud) is controlled via input from the main hydraulic pump pressure sensor(s). The two speed solenoid is usually in the same manifold as the pilot lockout and the swing brake solenoids. Said manifold will also have the pilot accumulator attached (looks like a softball/ baseball). I'm not sure if a 311 has one pump or two. Usually, the pump pressure sensor will generate a fault code, as will a faulty two speed solenoid. Fault codes and the pressure sensor output can be viewed through the display monitor.
there is a diagnostic mode in the 311B let me know if you can access it, you can see if the switch is being detected by teh computer first. If that is ok (probably is since the light is changing from Rabbit to tortoise) then you can also try and force the solenoid from the computer. The solenoid is one of the 4 solenoid in teh bank near the pump. You could check if this is working by hooking up a multimeter. So that would check out the wiring is all ok. If the wiring checks out you would have to replace the solenoid PNO is 121-1491 (red dot solenoid). its around a 100 bucks for a good copy. The solenoid you are after is the second one from the back of the excavator.
Thanks to you both! I’ve read a few posts in other threads on how to access the diagnostic mode. If you have instructions for entering the diagnostic mode in this machine and then testing the switch/solenoid from the diagnostic screen that would be very helpful!
Is this any help.?
send me your email I can send the manual part with all the codes when you get to the diagnostic screen
Thank you Nige and digger_hunter!
I just emailed to you let me know if you received it, its for a 320B but almost same stuff on 312B and 311B
#22 is the sensor responsible for the travel speed auto downshift.
nope that the pump pressure sensor
One of the four solenoids here is the rabbit solenoid. Power will be on one of them when rabbit is on. No power when rabbit is off.
When I had a whole bunches of 322B and 330B machines, that sensor would fail, and, no more rabbit.
no 4 red dot=travel speed solenoid
@digger_hunter I got the email, I’ll look it over and post back with questions. Thank you!
One more thought- I should check the solenoid wiring by carefully back probing the connector, correct? I am looking for voltage (24v?) when the rabbit is selected and no voltage when turtle is selected?
If you want a complete electrical schematic applicable to your machine please ask. You would be able to identify which solenoid is which by the wire numbers.
Yes, please @Nige ! I’ll take all the help I can get. Thank you!
PM sent.
Don't pierce nothing. Unplug solenoid in question. Turn key on. Enable pilot (flip up lever). Turn rabbit on. 24volt should be present at that connector. Unplugged, it'll have two socket pins you can test at. Next, ohm measure the pins in the solenoid. Record value. Plug that one back in and unplug adjacent one and measure ohms on solenoid. They should be within 5% of each other.
Sorry for the delay, I finally got back to look at this machine more last night. I unplugged the connector to the travel speed solenoid and did not see a change in voltage between the high and low speed selections from the cab. In fact, there was no voltage at all. I then measured the resistance in this solenoid (#4 in the pic digger_hunter posted above) and had 34.7 ohms. I compared this to the solenoid furthest forward (#2 in the pic above) which read 11.7 ohms. To be sure I then checked the resistance in the #3 solenoid and found 35.3 ohms. From the values published in the Cat electric schematic these solenoids all check out OK for resistance. Based on the lack of voltage to the solenoid I expect that this is the problem and there is a fault in the wiring somewhere between the cab monitor/switches and the solenoid. I’m not excited to look for this… I also checked the machine for fault codes and the only active code was 420C (voltage too low, probably because I had the machine off at this time). There were numerous stored codes but none that seem applicable to this issue. So, I guess my question at this point is, what can I do to test and see if this machine is stuck in high range (as the dealer tech said it was)? Honestly if it is in low range I’d probably just leave it alone since I really have little use for high range anyway. I just want to be sure I’m not going to damage the travel motors driving around in high range if that’s the issue. Any ideas? Also, a sincere thank you to @Nige @heymccall and @digger_hunter for helping me with this!
did you try on the test sheet to do item 62? Force travel solenoid one/off? does it work? if not probably the wiring between the computer and the solenoid is messed up. you could try reading between the positive and the chassis to see if there is any voltage that way just in case the ground wire is broken. if that's still no go you could check right at the computer which is underneath the seat if there's any voltage from the computer coming out. in the meantime you could try and forcing the solenoid by loosening the nut on top of the solenoid and then turning the screw down. Please mark the original position so you can return it to the original position. About a turn or 2 should force solenoid and hopefully switch to slow speed. We've seen a lot of the 312B/311B with the computer cover rusted through and the electronics damaged as all sorts of rubbish collect underneath the computer cover and floor of the excavator. And after a while the rust the breaks down teh cover and then exposes the electronics inside as well. Have had a few cases where there is no output from the pins on the computer but when w check the circuit there's power going right upto it and we have to bridge the path on teh board to the pin. But hopefully you don't have to go that far!
Couldn't you relieve the tank pressure, and after marking everything (wires and solenoids), swap the rabbit and pilot lockout solenoid. A) if you don't need the safety lever on to operate, when the suspect solenoid is in there, you've found the faulty solenoid (mechanically stuck, and would explain the stuck in rabbit). 2) since the pilot lockout solenoid works (I assume you need to flip the lever to operate), youll now have a known good solenoid in the rabbit hole. I don't have enough fingers to count how many times a pilot lockout solenoid failed, or was suspect, that I swapped it with the rabbit solenoid to ease in diagnosing, on my Caterpillars.
@heymccall that’s an interesting thought, I could do that to test it. @digger_hunter I did not try to force the solenoid from the diagnostic mode. Do you have instructions on how to do that?
Did u check pilot travel pressure switch ? Item 47
@DEMLONE70 I did not check that switch. It looks like I could swap it out with the one next to it to test it? It’s located on the valve bank above the swing motor, correct?
Yes it is on valve bank . One for travel One for implement
the travel solenoid has a different pro to the others so might not be interchangeable. Also try the section from the diagnostic I sent you. goto item 62 and you can force the solenoid on and off and at least figure out if the computer is at least trying to with the solenoid on and off. interim would be to force the solenoid on manually by adjusting the spool on the solenoid by turning the screw down.
but check voltage to ground instead of just across the pins, if you are lucky you could just have a bad ground and you can just splice the ground to a known good one if needed.
I had a few minutes after work tonight and so I checked the voltage to ground- nothing in either turtle or rabbit. Since I didn’t have time to swap the solenoid I unplugged it and turned it closed by three full turns. I did not find there to be a difference in travel speed. So, is this a definite indicator the machine is stuck in low speed not high speed? I will try swapping solenoids, performing the test of the solenoid from the monitor and check the pressure switch this weekend.
Considering your solenoid seems ok resistancewise. Please turn it back to where it was (spool screw). You could try following. I haven’t done this myself. But could work. Connect the safety solenoid connector to the travel solenoid. And since you are looking to swap them anyways, you could do it while it’s out and see if the solenoid gets activated when the safety lever is switched. If it does work then you have to check the outputs from the computer and either find the break in the wiring or put a couple of new wires from the computer to the solenoid (if the output from the computer is good that is). Could be a faulty computer as well in some cases. Anyways I will go through the wiring diagram when I have some time today and see what else we can do. Let me know how the swap goes
check pin 8 on the connector shown for output from computer. if its dead and you have a bad computer you could activate the solenoid by getting some power from an adjacent solenoid and could easily bodge a switch externally to turn the solenoid on and off.
check the attached your want pin 8 on Connector 24 (763BU) Blue wire
I think Cat wires have the wire code printed on them as well so you could look for that as the computer is a bit tight under the seat and all
@digger_hunter thank you very much for the help!! I’ll try to check this out over the weekend and post back with an update.
They do. The wire number (325 in the example below) is repeated every 6" or so along its length. So you're looking for a 14SWG Pink wire with 325 printed on it. There are a number of graphics and tables on every Cat electrical schematic that give useful information on how to decipher a schematic. It's well worth taking the time to read them, they will help you understand the schematic a lot better.
Curious did you ever sort this issue out. Have one doing similar currently
No, I narrowed my issue down to a wiring fault between the cab and the solenoid. But, I never had time to pull a new wire through and then ended up selling the machine. There was only one time I really wanted the two-speed when I had to walk it down a dirt road for a distance. I unplugged one of the neighboring solenoids (either fine grade mode or power mode I think) and plugged that connector into the two speed solenoid. In that configuration, high speed worked when I pushed the corresponding mode button on the display. That confirmed that I had a wiring fault for the two-speed circuit.