John Deere 3936.15 – ECU: Calculated Unintended Combustibles in DPF Slightly High

The engine controller has detected that the temperature differential between the Diesel Oxidation Catalyst (DOC) outlet and the Diesel Particulate Filter (DPF) outlet is abnormal. This temperature variance indicates the presence of unintended combustibles (such as unburned fuel, engine oil, or coolant) burning inside the DPF.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5085M
• 5100M
• 5100MH
• 5100ML
• 5115ML
• 5090M
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 6090MC
• 6100MC
• 6110MC
• 6105M
• 8310RT
• 8335RT
• 8360RT
• 9470RT
• 9520RT
• 9570RT
• 7760 Cotton Picker
• 7180-7980 Forage Harvesters
• 650K Dozers
• 210K-710K Backhoes
• 328E Skid Steer
• 332E Skid Steer
• 329E Compact Track Loader
• 333E Compact Track Loader

1. 1

   Perform a Cold Soak Temperature Sensor Check: Let the machine sit overnight and use Service ADVISOR to verify that DOC and DPF inlet/outlet temperature sensors read identical to ambient temperature before starting.

2. 2

   Inspect the fuel system for leaking fuel injectors, a faulty fuel dosing valve, or incorrect injection timing that could introduce unburned fuel into the exhaust.

3. 3

   Verify combustion efficiency to ensure the engine is not suffering from incomplete combustion due to low compression or restricted air intake.

4. 4

   Inspect the DOC and DPF for signs of physical damage, blockages, or excessive soot and fluid buildup.

5. 5

   Check for any exhaust leaks upstream of the DPF that could skew temperature readings.

1. 1

   Address the Root Cause

   Based on the diagnostics, repair the source of the unintended combustibles. This usually involves replacing leaking fuel injectors, fixing a faulty exhaust fuel doser, or repairing an internal oil/coolant leak.

2. 2

   Replace Faulty Sensors

   If the cold soak test revealed a failed exhaust gas temperature (EGT) sensor, replace it.

3. 3

   Clean or Replace the DPF/DOC

   If the DPF or DOC has been heavily contaminated by raw fuel, oil, or coolant, it must be removed and professionally cleaned (baked/blown out) or replaced entirely.

4. 4

   Reset the ECU

   After repairs are made, use a diagnostic tool to clear the 003936.15 fault code.

5. 5

   Perform a Forced Regeneration

   Initiate a parked active regeneration to burn off any residual soot and verify that the exhaust temperatures rise and fall within normal parameters without triggering the code again.