PACCAR Fault Code P3937: DEF Quality – Persist, Not Valid

Code details

Manufacturer

PACCAR (Kenworth & Peterbilt)

Applies to

PACCAR MX-13 (2017–2020)

Fault code

P3937

J1939 SPN

3364

FMI

2 — Data erratic, intermittent or incorrect

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 2 tells the shop the type of failure to test for: data erratic, intermittent or incorrect.
• Have a heavy-duty diesel technician confirm the fault against the engine or chassis service manual before replacing parts.

Related fault codes

• PACCAR Fault Code P1517 — Aftertreatment System – DEF Quality Malfunction Detected
• PACCAR Fault Code P3931 — DEF Quality Sensor ECU – Internal Error
• PACCAR Fault Code P3934 — DEF Quality Sensor Concentration – Voltage Too High or Short Circuit to Supply
• PACCAR Fault Code P3935 — DEF Quality Sensor Concentration – Voltage Too Low or Short Circuit to Ground
• PACCAR Fault Code P3941 — DEF Tank Level Sensor – Internal Error
• PACCAR Fault Code P3940 — CAN – Message Time-Out from DEF Tank Level Sensor
• International Fault Code SPN 3364 FMI 13 — Aftertreatment 1 Diesel Exhaust Fluid Tank Quality: Out Of Calibration