3516C Locomotive Engines Selective Catalytic Reduction Caterpillar

Use this procedure in order to troubleshoot a problem with a high differential pressure across the Clean Emissions Module (CEM). The pressure is measured between the engine exhaust intake for the CEM and the treated exhaust leaving the CEM. Use this procedure if the following event code is active. Refer to Troubleshooting, "Event Codes" for information about event codes.

Table 1

Event Code
Code and Description	Conditions which Generate this Code	System Response
E942 (1) High Aftertreatment #1 SCR Catalyst Differential Pressure	The differential pressure is above the trip point for the programmed delay time.	The code is logged. Dosing is disabled until the pressure is correct.
E942 (2) High Aftertreatment #1 SCR Catalyst Differential Pressure

Note: Use Cat ET to verify any suspected code. Determine what codes are present. Evaluate all codes for possible interaction. Refer toTroubleshooting, "Diagnostic Trouble Codes" and Troubleshooting, "Event Codes" for direction.

Probable Causes

• Plugged sensor lines

• Damaged components

• Failed sensor

• Plugged Diesel Oxidation Catalyst (DOC)

• Plugged Selective Catalyst Reduction (SCR) catalyst

• Plugged Ammonia Oxidation (AMOX) catalyst plugging

Recommended Actions

Plugged Sensor Lines

Inspect sensor lines for plugging with frozen condensate or foreign material.

Damaged Components

Inspect the sensor and wiring harness for damage and replace if necessary.

Failed Sensor

Determine if the exhaust gas differential pressure sensor has failed and replace if necessary.

Plugged DOC

Remove the DOC inspection cover and check the DOC for plugging with soot or oil.

Plugged SCR catalyst

Remove SCR inspection cover and check for SCR catalyst plugging with soot, oil, or DEF deposits.

Plugged (AMOX) catalyst

Remove the inspection cover and check for Ammonia Oxidation (AMOX) catalyst plugging with soot, oil, or DEF deposits.