Volvo ec330blc not starting

I’ll do the relay and switch you suggested. We are getting fuel at the filter. The Fuel gauge is showing 1 bar. It flashes when low fuel. I’ll ad fuel to be sure gauge is working. I’ll Report back tomorrow. Thanks.

Tried the relays with no luck. Switched the black switch and it cut the display off but still not starting. Just rolls over no exhaust smoke.

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while you've been trying to start the machine have you run the batteries down at some point, that could have given the fault code that was on the display and leaving a red herring that code shows as below
Fault mode
FMI 1
Detection conditions:The vehicle control unit (V-ECU) registers: that the voltage is below 18.5 V(VB15/VB16)
Symptom:
○ Red central warning
○ Buzzer sounds one time
○ Error message screen
○ V-ECU function can not work correctly
Possible causes:
○ Defective alternator
○ Defective battery, battery cables
○ Loose connection
Action Alternator, checking charging voltage

hence why your original guy said replace batteries. just to try to rule that out

I have 240blc that has had a similar problem. It took me a long time to locate the problem, I went through the same stuff you did. if it was 54 degrees and above outside it would fire right up, 53 degrees and lower she would just crank and crank no smoke. The engine ECU behind the cab had a barometric Pressure sensor in it that went bad. The only way to find out was to put a torch or a heat gun to the metal box and warm it up. It would trick the sensor and fire right up like it for 8 hours.

Yes Batteries have run down before. New batteries have plenty charge. Is there a way to erase error codes? This no start issue is not a low temperature issue because its been plenty of warm days and still wouldn't start.

When all else fails, look for.......