PACCAR (Kenworth & Peterbilt)
PACCAR fault code
SPN 3936 / FMI 12
PACCAR Fault Code P3991: Exhaust Gas Temperature Sensors ECU – Software Verification Incorrect
P3991 on PACCAR (Kenworth & Peterbilt) engines means: Exhaust Gas Temperature Sensors ECU – Software Verification Incorrect. The failure mode (FMI 12) is “bad intelligent device or component”.
Code details
- Manufacturer
- PACCAR (Kenworth & Peterbilt)
- Applies to
- PACCAR MX-13 (2017–2020)
- Fault code
- P3991
- J1939 SPN
- 3936
- FMI
- 12 — Bad intelligent device or component
- Truck models in source
- Kenworth T680, T880, W900, T800; Peterbilt 579, 389, 567, 367
What to do next
- Read active and inactive codes with the OEM service tool and note the occurrence count.
- FMI 12 tells the shop the type of failure to test for: bad intelligent device or component.
- Have a heavy-duty diesel technician confirm the fault against the engine or chassis service manual before replacing parts.
Get this code diagnosed
Send one request and nearby diesel shops and mobile mechanics can quote the repair.
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Related fault codes
- PACCAR Fault Code P3991 — DOC DPF Temperature Sensors ECU – Software Verification Incorrect
- PACCAR Fault Code P3802 — Diesel Particulate Filter (DPF) – Filter Severely Damaged
- PACCAR Fault Code P3788 — DPF Filtration Efficiency – Data Valid But Too Low, Moderately Severe
- International Fault Code SPN 3936 FMI 0 — DPF Soot Load – Severe Derate
- International Fault Code SPN 3936 FMI 14 — DPF – Regen Duration Above Limit
- International Fault Code SPN 3936 FMI 2 — DPF System Feedback Control Fault
- International Fault Code SPN 3936 FMI 20 — DPF Feedback Adaptive Limits Reached
- International Fault Code SPN 3936 FMI 8 — DPF – Regenerations Are Occurring Too Frequently
Source: PACCAR MX-13 2017–2020 fault code list (Diesel Laptops). See also OBD-II codes.