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Power Supply Lost With Ignition On – Data Erratic, Intermittent, or Incorrect
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Overview
| CODE | REASON | EFFECT |
| Fault Code: 1117 PID: S251 SPN: 627 FMI: 2/2 LAMP: None SRT: |
Power Supply Lost With Ignition On – Data Erratic, Intermittent, or Incorrect. Supply voltage to the ECM fell below 6.2 volts momentarily, or the ECM was not allowed to power down correctly (retain battery voltage for 30 seconds after key OFF). |
Possible no noticeable performance effects or engine dying or hard starting. Fault information, trip information, and maintenance monitor data can be inaccurate. |
 ISX and ISM – ECM Power Supply Circuit
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Circuit Description
The electronic control module (ECM) receives constant voltage from the batteries through the unswitched battery wires that are connected directly to the positive (+) battery post. The ECM receives switched battery input through the vehicle keyswitch wire when the vehicle keyswitch is turned on.
Component Location
The ECM is connected to the battery by the OEM power harness through the ECM battery supply stub. This provides a constant power supply for the ECM. The location of the battery will vary with the original equipment manufacturer (OEM). Refer to the OEM service manual.
Conditions for Running the Diagnostics
This diagnostic runs continuously when the keyswitch is in the ON position.
Conditions for Setting the Fault Codes
The ECM detects that primary ECM power supply dropped below 6.2-VDC while the keyswitch was in the ON position. The fault code will be active when the keyswitch is turned on following the incomplete power-down event.
Action Taken When the Fault Code is Active
- The ECM records the fault code immediately when the diagnostic runs and fails.
- Power-down data like trip information, maintenance monitor, and fault information will not get saved to permanent memory when the keyswitch is turned off.
Conditions for Clearing the Fault Code
The ECM must see primary ECM battery voltage above 6.2-VDC when keyswitch is turned off before the fault code will go inactive.
Shop Talk
Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe® Online for applicable fixes to the calibration stored in the ECM. If necessary, recalibrate the ECM. See the corresponding Service Manual for the engine being serviced.Refer to Procedure 019-032 in Section 19.
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 1117 active.
An active Fault Code 1117 can prevent critical aftertreatment soot load information from being saved to permanent memory in the ECM. Use of battery disconnect switches to turn off the engine or any device that disconnects battery voltage to the ECM within 10 seconds of turning the keyswitch off can cause damage to the aftertreatment system. The vehicle should not be operated with an active Fault Code 1117.
Refer to Troubleshooting Fault Code t05-1117
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