U1800 DTC Code
 

I installed a Banks OttoMind 6 Diesel Tuner and PDA in my 2003 Chevrolet 3500 Duramax 6.6 and now the truck won't start. I removed the Banks unit and went back to the factory setup, but it does the same thing, cranks but won't start. There is a U1800 DTC code when I throw the scanner on the OBDII connection. If I clear the code it comes right back. Any help would be appreciated.

Lost Communications With Fuel Injector Control Module (FICM)

Check the fuse then try the relay if that does not work.

Your problem is most likely in the two large BALE CONNECTORS where the Banks plugs in.

Dave, if your truck does not start and throws the DTC U1800, the fault could be in the FICM or the FICM power and ground circuits.

Disconnect the batterys and double check the FICM connectors for any debris.

I swapped the relays yesterday, but it made no difference. I looked for the fuse, but I cannot find one that is labeled FICM. The batteries have also been run down. They are still the originals. It seems to crank over ok when the batteries have been recharged, but I have read some posts on other sites that weak batteries may have something to do with the communication problem between the FICM and the ECM causing the U1800 code. Any thoughts on the fuse location or the possibility of the batteries causing the problem?

if the truck is only giving you only the U1800 code the problem is just in the FICM or the FICM power and ground circuits.

I believe the fuse is in the Junction block underneath the hood, it is a 25amp fuse i think its called INJ B Fuse

But its probably something in the wire harnesses you fiddled theres probably a short somewhere in there, but before you mess with that again unplug the batteries

any updates?

Thanks for all your help. It turned out to be the FICM.

cool

Yes, when you continually cranked the truck with weak batteries you actually increased the current draw across the FICM. Thats most likely what fried it.