Cummins ISB CM850 (2003-06) Fault Code: 434 PID: SID 251 SPN: 627 FMI: 2 Power Supply Lost With Ignition On – Data Erratic, Intermittent or Incorrect. Supply voltage to the ECM fell below 6.2 VDC momentarily, or the ECM was not allowed to power down correctly (retain battery voltage for 30 seconds after key OFF).

This fault is set active if the ECM battery supply voltage drops below 6.2 VDC while the keyswitch is in the ON position.

Make sure the ECM unswitched battery supply is coming directly from the battery and not the starter. If unswitched power is coming from the starter, it is possible for the battery voltage to drop low enough during cranking to set this fault active.

This fault can also be caused by resistance in the ECM battery supply (+) or (-) circuits. Resistance in these circuits can cause the voltage level at the ECM input to drop low enough to set Fault Code 434 active.

This fault can also be caused by a short to ground in the injector wiring harness. Check the injector wires are oriented so that they will not interfere with a rocker lever or other component in the overhead system. Remove the valve cover and check for proper alignment of the injector wiring harness.

On-Board Diagnostics (OBD) Information (Euro 4 Certified Engines):

1)The ECM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
2)The ECM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. The MIL lamp and fault code can also be cleared using the INSITE? service tool.
3)The fault code will be cleared from memory after 40 consecutive drive cycles where the diagnostic runs and passes.
On-Board Diagnostics (OBD) Information (Euro 4 Stage 1+ Certified Engines):

1)The ECM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
2)An engine torque derate will be activated after 50 hours of engine operation with the fault code active.
3)The ECM turns OFF the malfunction indicator lamp (MIL) after 1 ignition cycle that the diagnostic runs and does not fail. The MIL lamp cannot be cleared using the INSITE? service tool.
4)The fault code will be cleared from memory after 400 days or 9600 hours of engine operation.

Possible repairs:

1)Tighten the loose connections, and clean the terminals.
2)Charge or replace the battery.
3)Align and route the injector wiring harness so it does not touch the rocker levers.
4)Repair or replace the OEM harness.
5)Replace the blown fuse(s).
6)Repair or replace the OEM power harness from the OEM power connector to the batteries.
7)Repair or replace the ECM power harness.