Freightliner fault codes
10 codes documented, sorted by how urgent each one is. Every page carries the parts, the labour hours, and whether you can keep driving.
Out of service
- SPN 46 FMI 1Pneumatic Supply Pressure — Below Normal, Most SevereAir system pressure is below the level the brakes need. This is a brake system fault, not an engine fault. Do not move the truck on the theory that it will build back up.
- SPN 5246 FMI 0SCR Operator Inducement — Most Severe Level ActiveThis is not a warning. The emissions system has escalated to full inducement and the truck is about to be limited to a speed you cannot safely use on a public road. Get it somewhere safe now.
Derate risk
- SPN 1569 FMI 31Engine Protection Torque Derate — Condition ExistsThis code is not a fault. It is the truck telling you it has already cut power because of something else. Find the other code — that is the repair.
- SPN 3251 FMI 0DPF Differential Pressure — Above Normal, Most SevereBackpressure across the particulate filter is high enough that the engine is being protected. Either the filter is genuinely loaded, or the pressure sensor and its tubes are lying to you.
- SPN 3364 FMI 2DEF Quality / Concentration — Data Erratic or IncorrectThe truck thinks your DEF is the wrong concentration or the quality sensor is giving impossible readings. It is usually the DEF or the sensor, not the engine. Fix it before the inducement clock runs out.
- SPN 3719 FMI 0DPF Soot Load — Above Normal, Most SevereSoot load has passed the point where a normal regeneration will recover it. Do not keep driving hoping it burns off — at this level a forced regen can damage the filter.
- SPN 4364 FMI 18SCR Conversion Efficiency — Below Normal, Moderately SevereThe catalyst is not converting enough NOx to meet the certified standard. This is the fault that starts the inducement countdown — it does not clear itself and it does not wait.
Caution
- SPN 168 FMI 1Battery Potential / Power Input 1 — Below Normal, Most SevereSystem voltage is below what the electronics need. Left alone this ends with a truck that will not restart — and on a modern truck, low voltage also throws phantom fault codes all over the bus.
- SPN 3216 FMI 16SCR Inlet NOx Sensor — Reading Above Normal RangeThe NOx sensor before the SCR catalyst is reporting more NOx than the engine should be making. Usually a drifting sensor or an EGR problem upstream — not the catalyst itself.
- SPN 3226 FMI 16SCR Outlet NOx Sensor — Reading Above Normal RangeToo much NOx is getting past the SCR catalyst. Either the system is not dosing enough DEF, the catalyst has lost efficiency, or the outlet sensor is lying. All three are worth catching now.
Shops that work on Freightliner
We call every shop before it appears here, and publish the date.
Sample records only — seeded to demonstrate the directory. None of these numbers has been called.
Memphis, TN · 24/7 · mobile service
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