My local municipality has an 02 Cat 420D backhoe for sale. I went a looked at it this morning, not knowing what kind of shape it was in. The machine is obviously used, but seems fairly sound. But, there’s two indicator lights on on the cluster. One is obviously oil. The other I’m guessing is differential, or locking differential. The machine runs fine and is obviously pumping oil, but not sure on what would be the next step to correct the oil light. The 4x4 or differential, not sure on that at all. Anyone have any suggestions with these lights? Thanks in advance.
Were those two warning lights with the engine running or just with the key on.? If it was with the engine stopped did they go out when it was started.? The first one is low engine oil pressure. The 2nd one looks a bit like the implement hydraulic filter warning or maybe some general hydraulic system failure but I’d have to double check that. Do you have the machine Serial Number.?
Those were with engine running. I’ll check to see if they posted the serial number.
CAT0420DKFDP10018/KFDP10018
The low oil pressure light is controlled by a normally closed (NC) switch connected to ground. The switch contacts open when the oil pressure is above 10-14psi, which turns off the warning light. The fact that the light is staying on could be caused by a defective switch that is not opening, wiring that is permanently shorted to ground somewhere, or a deeper engine problem in that it actually DOES have low oil pressure. How did the engine sound when it was running.? The 2nd (amber) light is for a plugged implement hydraulic oil filter. When the machine warms up and the oils thins a bit there is a possibility that light might go out. Like the engine oil pressure light there is also the possibility of a defective switch or wiring.
The engine sounded fine. I cranked it from a cold start and it instantly fired up and we let it run for 15-20 minutes while checking the boom and bucket movement. There wasn’t an odd sound made. We pulled the dipstick to check the oil level and the oil was warm to the touch, like it had been circulating, but it might have been a fraction low. The bad part is, the city has it parked in their fleet bullpen and I couldn’t get the machine out to really work it, if you will. I‘ll ask a broad question….with the two trouble lights on and knowing what you hope can fix those, knowing the city bought this machine new in 02, it currently has 9800 hrs, would you be deathly afraid of the machine? Obviously, it’s been fleet maintained, which isn’t necessarily the best, but it could be worse. And, the machine isn’t flawless. It’s missing two pieces of glass and the cover on the colum that hides the brake pedal mechanism. But, it can be bought in the $7500 range. What are your thoughts? I do appreciate your knowledge and input!
I'm really the wrong guy to ask that question. I only fix 'em when dey is broko.......... TBH though if the engine sounded OK to you and it ran for 15-20 minutes then it's hardly likely (although still possible) it actually has low oil pressure. Fingers crossed most probably a switch or wiring with the oil pressure light. Question: When you first turned the key ON all the panel (gauges, lights, etc,) should have lit up and the warning buzzer should have gone off for a couple of seconds. Did that happen.? Regarding the hydraulic filter I would check the wiring first and if it tested out OK then I'd throw a new filter element into it.
Correct, the buzzer went off and the panel did light up all the idiot lights momentarily.
It seems strange that with low engine oil pressure being a level 3 alarm (warning light + buzzer) that you weren't driven demented by the buzzer going off all the time the engine was running..... "Engine Oil Pressure - The alert indicator will light and an audible alarm will sound when the engine oil pressure is low. If this alert indicator comes on, stop the machine immediately. Stop the engine and investigate the cause." Really the only way to confirm is to get a mechanical oil pressure gauge hooked up to the engine and do some measuring.
No buzzer beyond start up. What is the third gauge on the cluster, going left to right? Trans temp maybe? The gauge never would get off of cold during the short time we ran it. Which had me wondering if it was related to one of the trouble lights?
Which one in the illustration below.? #2 is tranmission oil temp. #4 is engine coolant temp.
Correction on my part….#2. The gauge never moved off of cold during our brief time running the machine.
It would probably take longer than 15-30 minutes to get that gauge to move if the machine had been started from stone cold.
That’s an excellent price if it is 4 wheel drive and it works. Around here, it would be 16 to 18k. The high hours, were probably put on idling. Suprised that the buzzer wasn’t going off with the presumed to be faulty oil pressure switch but someone probably did something to the ground for the switch because they were sick of hearing the alarm, just a guess.