Aftertreatment SCR Outlet Temperature - Data Erratic
What does CUMMINS-3742 mean?
The CUMMINS-3742 (Cummins) diesel fault code means: Aftertreatment SCR Outlet Temperature - Data Erratic. This is a moderate severity code.
Common Symptoms
- Amber check engine warning light
- DEF or DPF lamp illuminated
- Engine derate at 55 mph then 5 mph
- Failed active regeneration attempts
- Increased DEF or fuel consumption
Probable Causes (Ranked by Likelihood)
- Failed temperature sensor element Very Likely
- Wiring damage from exhaust heat Likely
- Connector corrosion at sensor body Likely
- Aftertreatment Control Module (ACM) fault Possible
- Exhaust leak affecting sensor reading Possible
Step-by-Step Diagnostic Procedure
Connect INSITE and read live data for the sensor tied to SPN 4766 -- compare against commanded value at idle and load.
Disconnect sensor and measure resistance across signal pins -- compare to Cummins service manual spec.
Inspect harness along exhaust routing for heat damage, rubbing, or melted insulation.
Check for exhaust leaks at clamps and gaskets upstream of the sensor location.
Repeat fault check after sensor replacement; if fault returns, suspect ACM (Aftertreatment Control Module) fault.
Frequently Asked Questions
What is Cummins fault code 3742?
Cummins fault code 3742 indicates: Aftertreatment SCR Outlet Temperature - Data Erratic. It is a moderate-severity fault in the aftertreatment or emissions system.
Can I drive with Cummins fault code 3742?
Yes, short-term driving is typically safe with fault 3742, but the fault will illuminate the Check Engine Light and must be diagnosed soon. Monitor for power loss, unusual noises, or gauge changes and pull over if conditions worsen.
How much does it cost to fix Cummins fault 3742?
Repair cost is approximately $300-$900 including parts, labor, and any dealer programming required. DIY repairs (sensor replacement) fall at the low end; pump, aftertreatment, or ECM work falls at the high end and usually requires INSITE diagnostic software.