Detroit Diesel Fault Codes
Detroit DD13 and DD15 fault code reference: SCR conversion efficiency, DEF quality, DPF soot loading, NOx outlet sensor, and J1939 aftertreatment context.
Detroit DD13 and DD15 aftertreatment fault codes are among the most frequently searched codes in long-haul and regional trucking. Key verified records include SCR conversion efficiency (SPN 4364 FMI 18), downstream NOx sensor (SPN 3226 FMI 16), DPF soot loading (SPN 3719 FMI 31), and DEF quality (SPN 3364 FMI 1). Use the fault code lookup to search all verified records by SPN or FMI.
NOx sensor and SCR efficiency codes often appear together, but they measure different things: SPN 3226 is the raw downstream NOx reading; SPN 4364 is the ECM's calculated conversion efficiency ratio. Both can be active at the same time, or one can be present without the other depending on which threshold the ECM has crossed. See the glossary for plain-English definitions of SCR, DPF, and NOx.
Aftertreatment fault codes on Detroit engines interact with an inducement system that escalates to a torque derate if root causes are not resolved. Diagnosis and repair should use Detroit DiagnosticLink and current GHG14 or GHG17 service information — not generic scan data alone. See the methodology page for how pages on this site are verified.
What To Know
- SPN 4364 (efficiency) and SPN 3226 (outlet NOx) measure related but distinct conditions — both should be checked.
- DEF quality and dosing problems cascade into SCR efficiency and NOx faults; start with the fluid.
- J1939 data link codes may indicate communication loss rather than a failed sensor or actuator.
- Stop safely when red stop lamps, engine protection derate, severe DPF loading, or critical temperature warnings are active.
FAQ
Which Detroit engines does this section cover?
The verified fault code pages focus on DD13 and DD15 engines, which share a common GHG14 and GHG17 aftertreatment architecture. DD16 uses the same J1939 SPN/FMI framework. Where diagnostic context differs between models, the individual code pages note it.
Are aftertreatment fault codes always sensor failures?
No. A NOx sensor code can originate from the sensor itself, but also from DEF quality, dosing quantity, catalyst aging, exhaust leaks, or wiring. SPN 4364 (efficiency) and SPN 3226 (raw outlet NOx) are related but distinct — diagnosing one without checking the other can lead in the wrong direction.
What is DiagnosticLink and why does it matter?
Detroit DiagnosticLink (DDL) is the OEM service software for DD-series engines. It provides live data, fault code history, component tests, and inducement reset capabilities that a standard scan tool does not have. Many aftertreatment procedures — including inducement resets — require DDL by design.