Diagnostic Overview
MaxxForce fault code SPN 2637 generally belongs in the aftertreatment monitoring group and may relate to DPF regeneration, exhaust temperature control, or aftertreatment system performance depending on the engine and calibration. The ECM may be seeing that the exhaust system is not responding as expected during regeneration or that an aftertreatment sensor value is outside the expected range. Because the FMI is not provided, this should be treated as a fault-code family rather than a complete diagnosis.
Likely Causes
Failed exhaust temperature sensor, DPF restriction, incomplete regeneration, exhaust leak, sensor wiring issue, incorrect aftertreatment sensor data, or upstream engine condition creating excessive soot.
What To Check First
Pull the full SPN/FMI, check active and inactive aftertreatment codes, review regen history, inspect exhaust temperature sensor wiring, and compare live exhaust temperature readings.