Good afternoon, could someone tell me what this indicator on Caterpillar P5000 indicates, which looks like a type C battery with an exclamation point?

E-34 Open in ignition coil primary circuit,
check for 12 volts to each coil, there should be battery voltage to each coil when the key is turned on, I forget the color on cat harness, maybe red with white stripe, I believe it is the one on the left looking at it from backside of connector, if none have 12 volts check egi relay circuit, this code will only set if you have an open in the primary circuit, check coils, and wiring, have had the issue from spread pins, from some one forcing meter leads into pins for testing, instead of back probing. Issues with these coils on the secondary side will usually set a code e-27 for the crank position sensor.

You didn't mention model #?
Can be bad coil...does it misfire. Are you clearing the codes. Wiring to module can be rotten as well....
Get truck up on blocks, running in gear , pinch wiring harness for breaks to see if any changes occur.