P207F – Reductant Quality Performance

Meaning of Code P207F:
This code indicates a problem detected by the vehicle’s diagnostic system related to the NOx sensors or their communication in the exhaust gas aftertreatment system (SCR). These sensors measure nitrogen oxides before and after the SCR catalyst to monitor its efficiency and the dosing of the additive (diesel exhaust fluid).

Possible Causes:

1. Failure of NOx sensors/modules:

   • Faulty upstream (before SCR) or downstream (after SCR) sensor.

   • Associated electronic module faulty.
     → Important: Sensor + module form a non-removable assembly. Upstream/downstream assemblies are not interchangeable.

2. Diesel exhaust fluid (AdBlue®/DEF) issue:

   • Degraded, diluted (e.g., with water), or incorrect specification fluid.

   • Crystal deposits in the DEF injector vent tube.

3. SCR catalyst failure.

4. Exhaust system leak (distorting measurements).

5. Electrical/communication problems:

   • Damaged wires, oxidized connectors, bent/broken pins.

   • J1939 communication network failure (linking NOx modules to engine control unit).

Symptoms:

• ⚠️ Check engine light on (or “Service Engine Soon”).

• Possible reduction in engine power (limp mode).

• Possible increase in pollutant emissions.

Diagnostic/Repair Procedure:

1. Initial check:

   • Check the quality and level of DEF fluid. Replace if doubtful.

   • Visually inspect the exhaust system for leaks.

2. Electrical inspection:

   • Carefully examine the wiring harnesses and connectors of the NOx sensors (upstream & downstream).

   • Look for: cut/chafed wires, improperly engaged connectors, oxidized, bent, broken, or backed-out pins.

3. In-depth diagnosis (requires specific tool):

   • Use a diagnostic tool to:

     • Read specific fault codes from the NOx modules (internal failures reported via J1939).

     • Check real-time values of the NOx sensors (upstream vs downstream).

     • Test communication on the J1939 bus.

4. Probable solutions:

   • Replace the faulty NOx sensor + module assembly (upstream or downstream based on diagnosis). Never interchange assemblies or separate sensor/module.

   • Clean or replace the DEF injector if clogged with crystals.

   • Replace the SCR catalyst if ineffective (after ruling out other causes).

   • Repair damaged wires/connectors.

Important:

• This fault often requires professional diagnosis with a dedicated tool.

• NOx modules are “intelligent” and self-diagnosing: the codes they send to the PCM guide the repair.

• The check engine light (MIL) turns off automatically after 2 successful drive cycles following the repair.