FC 3253 — Aftertreatment DPF Intake Temperature – Above Normal, Moderately Severe (SPN 3242 FMI 16) — Cummins ISX15

Diagnostic reference for Cummins ISX15 (2010–2017) CM2250/CM2350 with Cummins FC 3253.

Updated October 15, 2026

What it means

Cummins FC 3253 maps to SPN 3242 FMI 16. The ECM reports the temperature at the DPF intake is higher than expected, moderately severe. On the ISX15 this code is associated with the DPF and temperature sensors.¹

Most likely causes

1. Excess fuel reaching the aftertreatment from a doser or injector problem — Unintended fueling can raise DPF inlet temperature. Typical on this platform for FC 3253.¹
2. DPF intake temperature sensor fault or wiring issue — A faulty sensor or circuit can report an abnormally high temperature.¹

How to diagnose

1. Verify the code is active and note freeze-frame conditions (engine load, speed, regen state).
2. Inspect DPF intake temperature sensor and harness for damage, corrosion, or poor connections; check sensor reading vs. a known-good reference or compare to adjacent temperature sensors.
3. Review recent regeneration history and fueling-related codes; look for injector or doser-related faults that could cause excess fuel to reach the aftertreatment.
4. If sensor and wiring check good, monitor live DPF inlet temperature during operation and compare to expected values for the current operating condition.
5. Clear codes after repairs and road test to confirm the fault does not return.

Parts and tools you may need

• Diagnostic scan tool capable of Cummins FC/SPN/FMI
• Multimeter
• Wiring repair kit
• Replacement DPF intake temperature sensor

Tools you’ll need

• Cummins Insite diagnostic software — Reads SPN 3242 FMI 16 live data and freeze-frame to confirm DPF intake temperature anomaly during regen.
• digital multimeter — Checks DPF intake temperature sensor resistance and wiring continuity to rule out sensor or harness faults.
• infrared thermometer — Provides a non-contact temperature reference at the DPF inlet to compare against ECM-reported values.
• OBD-II scan tool — Retrieves active and historical codes to identify related injector or doser faults causing excess fueling.

Rough cost and difficulty

Typical US independent-shop figures; labor runs about $140–$200 per hour (dealers charge more). Confirm the diagnosis before buying parts.

When to see a pro

If the temperature reading remains high after sensor and wiring checks, or if active fueling faults are present, have a certified Cummins technician evaluate the engine and aftertreatment system. High-pressure fuel and aftertreatment work require specialized tools and safety precautions.

Check for recalls

Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.

Sources