SPN 168 - FMI 18 (Fault Code 441)

SPN 168 - FMI 18 (Fault Code: 441)
SPN168 FMI18
ISB, ISC, and ISL with CM2150 - Unswitched Battery Supply

Fault Code: 441
PID(P), SID(S): P168
SPN: 168
FMI: 1/18

REASON: Battery 1 Voltage - Data Valid but Below Normal Operational Range - Moderately Severe Level. ECM supply voltage is below the minimum system voltage level.

EFFECT: Engine may stop running or be difficult to start.

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. There is one 30-ampere fuse in the unswitched battery wires to protect the original equipment manufacturer (OEM) harness. The ECM receives switched battery input through the vehicle keyswitch wire when the vehicle keyswitch is turned on. The battery return wires are connected directly to the negative (-) battery post.

Component Location:
The ECM is located on the intake side of the engine. The ECM is connected to the battery by the OEM harness. This direct link provides a constant power supply for the ECM. The location of the battery will vary with the OEM.

Conditions for Running the Diagnostics:
This diagnostic runs continuously when the keyswitch is in the ON position or when the engine is running.

Conditions for Setting the Fault Codes:
The ECM detects that the main battery supply voltage is less than 6-VDC.

Action Taken When the Fault Code is Active:
• The ECM logs the fault code immediately when the diagnostic runs and fails.

Conditions for Clearing the Fault Code:
The ECM will turn off the fault code immediately after the battery voltage is above +6-VDC.

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.

This fault code is logged when the ECM battery supply voltage drops below 6-VDC.

• Verify that the ECM unswitched power supply is coming from the batteries and not the starter or other device. Check for possible weak batteries.
• If the ECM unswitched battery supply is taken from the starter, check for low voltage during cranking. Low voltage during cranking can cause the ECM power supply to drop below specifications and log Fault Code 441.

Read More:
SPN 168 - FMI 16 (Fault Code 442)
SPN 100 - FMI 2 (Fault Code 435) CL


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