My cat 303cr (s/n dma04209) blows the sm fuse when I switch the ignition switch from on to start. it won’t crank over at all. all other fuses are good I checked with continuity including the 50 ampers under the seat. At first it would turn over to start and I could start it but the fuse would need to be replaced the next time I needed to start it. Then it developed into turning over for a couple of seconds and then blow the fuse. Now it blows it upon switching ignition from on to start. I’ve been messing with this issue for a couple of weeks on and off now. Any help/ideas would be greatly appreciated thank you
Firstly i am not familiar with your machine. I would greatly speed up things if you had a wiring diagram. The switch is probably energizing two or three circuits not just the starter. Starter/Glow/Safety interlock come to mind. If you are lucky there might be push on terminals on the wires down stream of the sm fuse. The offending wire might be one of them so pull them off and energize them separately. To minimize messing up your wiring harness you would normally start with the obvious and work backwards. I would check all the wiring loom around the engine bay and started looking for any rubbed wiring shorting to ground. You could make shore the machine is safe to start and run an external wire to the starter solenoid and check the coil is not drawing excessive current. Assuming all good the next most common things to check would be glow plugs and associated wiring and relays. It is uncommon for starter solenoid to have a intermittent short which would result in it still continuing to start. All the micro switches on seat and neutral position and so on can get damaged easy. What size is the fuse that is being blown?
Good day It may not be applicable, however I recall reading that there was a start switch upgrade - modification for the 303, I'm not sure of the details, maybe one of the Cat guys can elaborate. Kind regards Uffex
The switch upgrade was for all machines from first built up to DMA03508, so the OP's machine came ex-factory already with the upgrade.
It’s a fifteen amp fuse that was in there and that’s what it says in the fuse box cover so that’s what I put in it. But in the book it said something about a thirty amp fuse but the fuse box seems all wrong so I didn’t want to put a thirty amp fuse in it
As mentioned above there was an update made by the factory to the starter switch from DMA03508-Up that involved installing an additional relay in the starter circuit. On both the electrical schematic and the parts list Machines up to DMA03507 show a 30-amp fuse in the circuit for the starter switch. Machines DMA-3508-Up show a 15-amp fuse in that same circuit, again in both the schematic and the parts. However the O&M Manual shows a 30A starter circuit fuse for all DMA machines. It has not been amended to the latest information regarding the starter circuit. I wonder if the problem could be in the starter switch relay or the relay circuit.?
I had similar problem with a 301.6, had a bad wire harness from chaffing changed it out completly no more blown fuses
I don’t think my machine had the update there is no additional relay unless I haven’t torn it down far enough. I took the top cover off with the starter switch and the gauge box with the whole wiring harness going straight down into the floor. No relays
Sorry if I confused you. I was trying to explain why your particular machine has a 15amp fuse in a location where, according to the O&M Manual information posted by HMC, there should be a 30 amp fuse. The document I posted above is the field retrofit procedure for all machines from first built up to S/N SMA03508. Your machine had the update installed from the factory but the parts are in a different location. See the attachment, the start relay is Ref #2. My point was that a problem with the start relay or the wiring for the start relay could be causing the fuse to blow. I'll send you a copy of the appropriate electrical schematic for your machine.
Does anyone know where I could find a wiring diagram for this machine? I know the starter and solenoid is good. If you jump the solenoid to power it fires right up.
I see that you posted the Serial Number of your machine above. I’ll send you an electrical schematic.
To the OP - check your message inbox.
I’ll make sure I post what all we do to this to keep you updated thank you all very much
Just remember that as per the information above a 15A fuse in the starter circuit is the correct amperage for your Serial Number (because of the wiring updates made ex-factory above DMA03508) despite what the Operation & Maintenance Manual might say to the contrary. The schematic I sent you lists 15A in that location.
This issue has been resolved with a new starter/starter solenoid. The solenoid was the real issue. Thank you all for your help