SPN 191 - FMI 18 (Fault Code 489)

SPN191 FMI18
Transmission Output Shaft Speed - Data Valid But Below Normal Operating Range - Moderately Severe Level

Auxiliary Speed and Pressure Input Circuit

Fault Code: 489
PID(P), SID(S): P191
SPN: 191
FMI: 1/18
Lamp: Amber

REASON: Low auxiliary speed signal frequency has been detected.

EFFECT: Possible reduced engine performance.

Circuit Description:
The transmission output shaft input is a frequency signal from an auxiliary speed or pressure pickup. It is sent to the electronic control module (ECM) and is used to control the engine speed. Auiliary reference speed is based on the accelerator position.

Component Location:
The transmission output shaft or pressure pickup device location is dependent on the original equipment manufacturer (OEM) application. Refer to the OEM service manual for component location.

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 Engine Control Module (ECM) detected a low frequency input that was below a calibrated threshold.

Action Taken When the Fault Code is Active:
• The ECM illuminates the amber CHECK ENGINE lamp and/or the malfunction indicator lamp (MIL) immediately when the diagnostic runs and fails.

Conditions for Clearing the Fault Code:
• To validate the repair, perform a key cycle, start the engine and let it idle for 1 minute.
• The fault code status displayed by the recommended Cummins® electronic service tool or equivalent will change to INACTIVE immediately after the diagnostic runs and passes.
• The ECM will turn off the amber CHECK ENGINE lamp immediately after the diagnostic runs and passes.
• The “Reset All Faults” command in the recommended Cummins® electronic service tool or equivalent can be used to clear active and inactive faults.

Shop Talk:
The transmission output shaft governor controls engine speed, based on a measured auxiliary speed or pressure.

Read More:
SPN 1189 - FMI 3 (Fault Code 491)
SPN 1189 - FMI 4 (Fault Code 492)


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