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Detroit Diesel SPN 3700 FMI 1 indicates that the temperature at the DPF outlet is below the minimum acceptable threshold. This code appears on DD13, DD15, and DD16 engines and signals that exhaust temperatures exiting the DPF are insufficient for proper aftertreatment operation. Low outlet temperatures can prevent effective regeneration and indicate issues with exhaust heat management or sensor accuracy.
Symptoms
- Check engine light on
- DPF or regen warning light illuminated
- Passive regeneration unable to complete effectively
- DPF soot load gradually increasing
- Reduced aftertreatment efficiency
- May appear alongside DPF inlet temperature low codes
Cause
This code triggers when the DPF outlet temperature sensor detects exhaust temperatures below the minimum required threshold after passing through the filter. Common causes include:
- Extended idling or light load operation preventing adequate exhaust temperatures
- Frequent short trips not allowing engine to reach full operating temperature
- Faulty or stuck open thermostat causing low engine and exhaust temperatures
- Failed DPF outlet temperature sensor giving false low readings
- Damaged or missing exhaust insulation causing excessive heat loss
- Engine running lean or misfiring reducing exhaust output temperatures
- Cold weather operation with light duty cycles
Can You Keep Driving?
Driving is possible but low DPF outlet temperatures indicate the aftertreatment system is not reaching the temperatures needed for effective regeneration. Soot will accumulate over time leading to more severe DPF faults if the root cause is not addressed.
Recommended Action
Check engine operating temperature and thermostat condition. Review the vehicle duty cycle for excessive idling or short trip patterns. Inspect the DPF outlet temperature sensor and wiring for damage or corrosion. Check exhaust insulation for damage that may be causing excessive heat loss between the DPF inlet and outlet.
It means the temperature exiting the DPF is below the minimum required threshold, indicating exhaust heat is insufficient for effective aftertreatment operation and regeneration.
The most common causes are extended idling, frequent short trips, a faulty thermostat causing low engine temperatures, a failed DPF outlet temperature sensor, or damaged exhaust insulation.
Driving is possible but ongoing low outlet temperatures will prevent effective regeneration and allow soot to accumulate leading to more severe DPF faults over time.
Not immediately but soot accumulation resulting from ineffective regeneration will eventually trigger DPF soot load codes and derate conditions.
Address the root cause of low exhaust temperatures — check the thermostat, duty cycle, and temperature sensor. Once DPF outlet temperatures return to the normal operating range the code should clear.
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.