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Detroit Diesel SPN 3251 FMI 18 indicates a fault with the DPF differential pressure sensor, which is the component the ECM relies on to measure the pressure difference across the Diesel Particulate Filter and calculate soot load levels. When this sensor fails on DD13, DD15, and DD16 engines the ECM cannot accurately monitor DPF condition, which can affect regeneration scheduling and lead to derate conditions.
Symptoms
- Check engine light on
- DPF or regen warning light illuminated
- Regeneration cycles may become erratic or not initiate
- Engine derate possible
- DPF soot load readings may be inaccurate
- May appear alongside DPF soot load codes
Cause
This code triggers when the ECM detects the DPF differential pressure sensor is reading outside the acceptable range. Common causes include:
- Failed or degraded differential pressure sensor
- Clogged or blocked pressure sensor lines or ports
- Damaged sensor wiring or connector
- Water intrusion at the sensor connector
- Cracked or disconnected pressure sensing tubes
- Carbon buildup blocking the sensor ports
- Faulty sensor giving implausible pressure readings
Can You Keep Driving?
Limited driving may be possible but without accurate differential pressure data the ECM cannot properly manage DPF regeneration. This can result in either premature or missed regeneration cycles, potentially leading to a soot overload condition and derate. Address this fault promptly.
Recommended Action
Inspect the differential pressure sensor lines and ports for carbon buildup or blockages — clogged sensor ports are a very common cause of this fault and are often overlooked. Check the sensor wiring and connector for damage or water intrusion. If the lines and wiring are clear and intact replace the differential pressure sensor as sensor failure is the next most likely cause.
It means the DPF differential pressure sensor is reading outside the acceptable range and the ECM cannot accurately measure the pressure difference across the DPF to determine soot load levels.
The most common causes are clogged sensor ports or lines, a failed differential pressure sensor, damaged sensor wiring, or water intrusion at the connector.
Short distances may be possible but without accurate DPF pressure data the ECM cannot properly manage regeneration cycles and a soot overload condition or derate may follow.
It can if the inaccurate pressure readings cause the ECM to miss regeneration cycles and allow soot to accumulate beyond acceptable levels.
Inspect and clean the sensor ports and lines first. If ports are clear check the wiring and connector. Replace the differential pressure sensor if it is faulty. The code should clear once the sensor is providing accurate readings within the expected range.
Related codes
Need Immediate Help With This Fault Code?
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Important Notice
The information provided above is for general informational purposes only and should not replace official OEM service procedures. Always consult the manufacturer’s service manual or a qualified diesel technician before performing repairs. Operating a vehicle with active fault codes may result in further damage.