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Caterpillar CR 303E

M

Mr. Wrench

Senior Member
Joined
Oct 23, 2025
Messages
381
Location
Ohio
Occupation
Mechanic
I'm having trouble with a 303e s/n SMG01318. It was working fine. They went to start it and it would not crank. The display lights up. None of the fuses are blown. It is not getting power to the start relay terminal 30. If I put power to terminal 87a, I think, with the key on it will start and work fine. I need to figure out why there is no power to the start relay. Does anyone have a wiring diagram? It would save alot of time chasing wires.
 
M

Mr. Wrench

Senior Member
Joined
Oct 23, 2025
Messages
381
Location
Ohio
Occupation
Mechanic
So I found the problem. Kind of dumb, but I didn't know.:rolleyes: They took the keys out of the machines. When they came back to move them they went around putting CAT keys in the the machines. This machine has a chip in the key. Once I found the right key for it the security light turned green and it started right up.
 
Baxsie

Baxsie

Well-Known Member
Joined
Oct 22, 2025
Messages
187
Location
Eastern Washington
I ordered spare keys from eBay for my 2018 CAT mini excavator. They were super cheap, fit fine, and look better than the one that came with it.

Too easy . . . for me or anyone else!

I think I'd rather have the chip!
 
Nige

Nige

Senior Member
Joined
Jun 22, 2011
Messages
38,559
Location
G..G..G..Granville.........!! Fetch your cloth.
Baxsie said:
I ordered spare keys from eBay for my 2018 CAT mini excavator. They were super cheap, fit fine, and look better than the one that came with it.
Click to expand...
That was the problem with the OP’s machine. Someone had put a “standard” key in a machine equipped with an MSS Security System. Such machines require the use of a key with a transponder in it. Said transponder deactivates the MSS and allows the machine to power up.
 
H

HarleyHappy

Senior Member
Joined
Sep 30, 2020
Messages
3,413
Location
So NH
Occupation
Welder/Mechanic
So you’re telling me, my Cat key from 35 years ago will still work?
I still have a milkcrate of Cat locks, I have been moving from home to home, from back when I did roadwork. Every new Cat we got came with locks on all the panels. Ended up just throwing them in a milk crate.
 
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