John Deere 3936 – ECU: Calculated Unintended Combustibles in DPF Extremely High

The system has detected multiple times that the temperature differential between the DOC (Diesel Oxidation Catalyst) outlet and the DPF (Diesel Particulate Filter) outlet is abnormally high. This indicates that unintended combustibles (such as raw unburned diesel fuel, engine oil, or coolant) are entering the exhaust stream and igniting inside the DPF, causing extreme temperature spikes that can severely damage or melt the exhaust filter substrate.

• 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
• 8310RT
• 8335RT
• 8360RT
• 8245R
• 8400R
• 9470RT
• 9520RT
• 9570RT
• 6105M
• S760
• 7760
• 624K

1. 1

   Check for accompanying codes related to the fuel injectors, fuel dosing system, turbocharger, or EGR system, as these are the primary sources of unintended combustibles

2. 2

   Inspect the fuel dosing injector (hydrocarbon doser) to see if it is stuck open or leaking raw fuel into the DPF

3. 3

   Check for mechanical leaks such as blown turbocharger seals leaking engine oil into the exhaust

4. 4

   Inspect the EGR cooler and head gasket for internal leaks allowing coolant into the exhaust

5. 5

   Check for faulty or leaking engine fuel injectors

6. 6

   Verify the DPF differential pressure sensor and its tubes are not blocked by soot, moisture, or installed in an incorrect orientation

7. 7

   Monitor live data using a diagnostic tool to observe DOC inlet/outlet and DPF inlet/outlet temperatures to verify the temperature differential is genuinely occurring

1. 1

   Resolve the Root Cause

   Repair or replace the component introducing the combustible fluid into the exhaust (e.g., replace a leaking fuel dosing injector, rebuild the turbocharger, or replace a leaking EGR cooler).

2. 2

   Inspect the Exhaust Aftertreatment System

   Remove the DPF and DOC to inspect the internal ceramic substrates. Look for signs of thermal damage, such as cracking, melting, or heavy face-plugging.

3. 3

   Clean or Replace the DPF

   If the DPF is heavily loaded with soot/ash but not melted, it must be sent out for professional pneumatic/thermal cleaning (baking). If the substrate is melted or cracked from the extreme heat, the DPF must be replaced.

4. 4

   Reassemble the Exhaust System

   Install the cleaned or new DPF using new gaskets and clamps.

5. 5

   Reset ECU Parameters

   Connect your diagnostic tool. Navigate to the ECU settings and perform the 'DPF Replacement' or 'DOC & DPF Replacement' routine. This resets the calculated ash/soot levels in the ECU so it knows a clean filter has been installed.

6. 6

   Clear Codes and Test

   Clear the latched 003936.00 fault code. Perform a forced parked regeneration to verify the system operates at normal temperatures and the fault code does not return.