SPN 3597 - FMI 18 (Fault Code 1938)

SPN3597 FMI18
ECU Power Output Supply Voltage 1 - Data Valid but Below Normal Operational Range - Moderately Severe Level

ISB, ISC, and ISL with CM2150 - VGT Actuator Circuit

Fault Code: 1938
SPN: 3597
FMI: 1/18
Lamp: Amber

REASON: ECU Power Output Supply Voltage 1 - Data Valid but Below Normal Operational Range - Moderately Severe Level. Low battery voltage detected by the VGT actuator.

EFFECT: None on performance.

Circuit Description:
The variable geometry turbocharger (VGT) is electronically activated by the VGT actuator. The VGT actuator is a smart device and receives information via the J1939 datalink from the primary engine ECM. The VGT actuator performs its own diagnostics and reports failures back to the primary engine electronic control module (ECM) using the J1939 datalink.

Component Location:
The VGT actuator is located on the turbocharger bearing housing.

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

Conditions for Setting the Fault Codes:
The fault code is set when the voltage supplied to the VGT actuator drops below +10-VDC for 10 seconds and the engine speed must be zero rpm or above 500 rpm.

Action Taken When the Fault Code is Active:
• The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
• The VGT actuation will continue until battery voltage drops low enough that VGT actuation can not continue.

Conditions for Clearing the Fault Code:
The ECM will turn off the amber CHECK ENGINE light immediately after the voltage to the VGT actuator is greater than +10-VDC and the engine speed is zero or greater than 500 rpm.

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.

This fault code is logged when the voltage to the VGT actuator drops below +10-VDC. The VGT will still continue to respond to commands from the primary engine ECM.

Read More:
SPN 157 - FMI 0 (Fault Code 1911)
SPN 3251 - FMI 16 (Fault Code 1921)


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