Overview

Code

Fault Code: 1981

PID: 

SPN: 3936

FMI: 0/15

LAMP: Amber

SRT:     

Reason

The aftertreatment differential pressure has exceeded the maximum operating limits or the diesel particulate filter is plugged.

Effect

Possible reduced engine performance.

Aftertreatment Diesel Particulate Filter Differential Pressure Sensor Circuit

Circuit Description

The engine aftertreatment system monitors the soot load in the aftertreatment diesel particulate filter. Under normal operating conditions, the aftertreatment diesel particulate filter is self-cleaning, where soot is converted to carbon dioxide, nitrogen, and water. Under light load operating conditions, it can be necessary to perform a stationary regeneration of the aftertreatment diesel particulate filter. The soot load in the aftertreatment diesel particulate filter is estimated, using the aftertreatment differential pressure sensor and the calculated soot output of the engine.

Component Location

The aftertreatment diesel particulate filter is located in the exhaust system and is installed by the original equipment manufacturer (OEM). Refer to the OEM service manual.

Conditions for Running the Diagnostics

This diagnostic runs continuously when the engine is running.

Conditions for Setting the Fault Codes

The Engine Control Module (ECM) detected the diesel particulate filter is plugged or that the differential pressure across the diesel particulate filter was greater than the maximum limits.

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.

Exhaust gas recirculation (EGR) valve operation will be disabled.

Active and stationary regeneration of the diesel particulate filter will be disabled.

Engine torque will be reduced if the engine is operated for an extended period of time with this fault active.

Conditions for Clearing the Fault Code

• To validate the repair, perform a key cycle, start the engine and run at high idle for 6 minutes.
• 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.
• For On-Board Diagnostics (OBD) engines, the ECM will extinguish the Malfunction Indicator Lamp (MIL) after three consecutive trips where 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, as well as extinguish the MIL for OBD applications.

Shop Talk

Possible causes of this fault code include:

The aftertreatment diesel particulate filter can be plugged with ash.

The engine has been operating in light load conditions that prevent exhaust gas temperatures from being high enough to actively regenerate the aftertreatment particulate trap.

An engine malfunction that is elevating the engine smoke output.

Excessive ash in the DPF

Reference the appropriate OEM wiring diagram when troubleshooting circuits that utilize wiring supplied by the OEM.

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