Applicable Systems
EMCP 4.2
Symptoms
SCR fault indicator active; engine derate at level 1 or 2; NOx conversion efficiency below threshold.
Possible Causes
- SCR catalyst degraded or poisoned
- DEF dosing valve clogged
- NOx sensor reading out of range
Troubleshooting Steps
- Step 1: Check NOx sensor readings (inlet vs outlet)
Outlet NOx < inlet NOx (conversion working) - Step 2: Inspect DEF dosing valve for clogging
Valve sprays evenly, no crystals - Step 3: Check SCR catalyst for physical damage
Catalyst intact, no cracking - Step 4: Clean or replace DEF dosing valve
Dosing valve flow within spec - Step 5: Clear code and perform drive cycle for SCR verification
NOx conversion > 70% at operating temp
How to Reset
Clear via Cat ET after SCR system repair and drive cycle.
Common Replacement Parts
- DEF Dosing Valve P/N: 385-7312
- NOx Sensor P/N: 385-7423
Frequently Asked Questions
- Q: Can I bypass the SCR system?
No. Emissions regulations require functional SCR. Bypassing will trigger permanent derate and violate emissions law.
Comments (0)
Share your experience to help others facing the same problem.
Leave a Comment
Source: verizonconnect.com DTC guide
Category: Heavy Equipment
No comments yet. Be the first to share your experience!