The MX-13 powers the majority of Kenworth and Peterbilt trucks sold since 2010. Its fault list runs through DAVIE4 with PACCAR's own code numbering over J1939 SPN/FMI — both shown here.
How PACCAR MX-13 fault codes work
DAVIE4 displays PACCAR P-codes (e.g., P1495) alongside SPN/FMI. The MX-13's EPA13+ aftertreatment is tightly integrated — most high-severity codes chain into the derate sequence quickly, so early diagnosis matters more on MX than on Cummins or Detroit.
Most-searched PACCAR MX-13 codes
These are the codes technicians look up most. Every row links to a full code page with symptoms, ranked causes and step-by-step diagnostics.
| Code | Meaning | Severity | Common fix |
|---|---|---|---|
| P1495 / SPN 3216 FMI 4 | NOx sensor voltage low | High | Sensor/harness |
| P207F / SPN 5246 | SCR derate inducement | Critical | Root repair + DAVIE4 reset |
| P228D / SPN 4334 | DEF pressure out of range | High | DEF pump module |
| P1039 | EGR valve position fault | High — MX signature fault | EGR valve cleaning/replacement |
| P0521 | Oil pressure sensor range | Medium | Sensor — verify with mechanical gauge |
| P20E8 | DEF dosing too low | High | Doser valve/filter |
| P150B (2017+) | Crankcase ventilation fault | Medium | CCV filter overdue — maintenance item |
Tools that read and clear PACCAR MX-13 codes
DAVIE4 is the correct tool — its guided EGR and aftertreatment tests are specific to MX architecture. PX-7/PX-9 engines are Cummins-derived and equally well served by INSITE; see the PX codes page. Multi-brand scanners read MX codes but miss the guided sequences.
Frequently Asked Questions
What is the MX-13's most common fault?
EGR valve position faults (P1039 family) — the MX EGR valve lives in a high-soot environment and sticks. Cleaning works early; replacement is inevitable around 400k miles. DAVIE4's EGR test confirms before you spend.
Why do MX-13 derates escalate so fast?
PACCAR's inducement schedule is aggressive by design — many aftertreatment faults start a 4-hour countdown immediately. Diagnose the first warning, not the derate.