PACCAR (Kenworth & Peterbilt)
PACCAR fault code
SPN 4355 / FMI 5
PACCAR Fault Code P3979: Heater Element DEF Return Pipe – Short Circuit to Ground or Open Circuit on ECU (D374) Pin (A52)
P3979 on PACCAR (Kenworth & Peterbilt) engines means: Heater Element DEF Return Pipe – Short Circuit to Ground or Open Circuit on ECU (D374) Pin (A52). The failure mode (FMI 5) is “current below normal or open circuit”.
Code details
- Manufacturer
- PACCAR (Kenworth & Peterbilt)
- Applies to
- PACCAR MX-13 (2013–2016)
- Fault code
- P3979
- J1939 SPN
- 4355
- FMI
- 5 — Current below normal or open circuit
- 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 5 tells the shop the type of failure to test for: current below normal or open circuit.
- 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 P3979 — SCR Exhaust Gas Temperature Sensors ECU – Voltage Too Low or Short Circuit to Ground
- PACCAR Fault Code P3980 — SCR Exhaust Gas Temperature Sensors ECU – Data Valid But Too High
- PACCAR Fault Code P3980 — Heater Element DEF Return Pipe – Short Circuit to Supply on ECU (D374) Pin (A52)
Source: PACCAR MX-13 2013–2016 fault code list (Diesel Laptops). See also OBD-II codes.