666: Canbus Failure - Engine Controller - No Start

Blown Fuse
Loose ground connection
Corrosion in the fuse holder
Broken wire or bad splice in the harness

1. Check ecm fuses and ground connections. Make sure the fuses have 12 volts.

A. Check the 30 amp fuse in the inline fuse holder in black box under the radiator. (Note: the fuse may look and test good but may be bad)

B. Check the F18 fuse in the cab fuse/relay panel.

C. Remove and clean the ecm ground on the side of the engine block beside the fuel filter.

2. If ecm fuses and ground is good but the 666 code is still on.

A. Remove the J2 connector from the ecm to test power and ground through the harness to the ECM.

1. Power from the 30 amp ecm fuse will be on pins 1, 25, 26, 27 and 28.

2. Power from the F18 fuse will be on pin 5. (Note the keyswitch has to be in the on position to see power on this pin)

3. Engine block ground in on pins 49, 50, 51, 52 and 73.

3. If there is not power or ground on the correct pins. Then the harness will need to be tested for broken wires or bad splices.

4. If there is power and ground to the correct pins, the ecm will need tested by Cummins or replaced. (Note: New ECM will need to be flashed with the correct Cummins's software by Cummins.)