A 2013 Ford Kuga recently came into a British workshop with an intermittent power loss and a single P246B fault code. We see this specific combination in our own data at Wrenchlane, and it usually points straight to the active exhaust fuel vaporiser system.
The technician recorded an intermittent power loss on this vehicle. The diagnostic platform we build ranked four primary causes for this exact failure pattern, giving us a clear path to test the components in order of probability.
Heating element failure in the fuel vaporiser
Our diagnostic engine ranked a failure of the DPF fuel vaporiser heating element, or its blown circuit fuse, as the most likely cause at a 72 percent probability with high severity. The 2013 Ford Kuga 2.0 TDCi with the UFMA Duratorq engine uses an active exhaust fuel vaporiser unit. This component sits directly in the exhaust downpipe upstream of the catalyst and DPF.
During active DPF regeneration on highway cycles, the powertrain control module commands the internal glow plug heating element to heat up while fuel is metered across it. This creates vaporized fuel that ignites in the catalytic substrate, elevating exhaust temperatures to 1,112 degrees Fahrenheit (600 degrees Celsius). The internal glow plug heating element frequently burns out into an open circuit or shorts to ground, which instantly blows its dedicated fuse in the engine junction box.
When the heating element fails, fuel cannot be vaporized or ignited. Exhaust gas temperatures never reach the regeneration threshold within the calibrated 13-minute monitoring window. The module consequently flags P246B, which means conditions are incorrect for regeneration, and activates an intermittent torque-reduction limp mode to protect the exhaust system.
To diagnose this, perform a continuity check on the DPF fuel vaporiser circuit fuse. You should also measure the internal glow plug resistance and use a scan tool to command the vaporiser relay output and run a supply voltage test.
Carbon coking in the fuel nozzle
Ranked second at 65 percent probability is carbon coking and blockage of the DPF fuel vaporiser nozzle. Even if the electrical glow plug remains intact, the small fuel atomizing discharge nozzle tip sits directly inside the harsh exhaust gas stream. Over time, soot agglomerates at the nozzle tip and completely seals the fuel orifice.
When the module detects suitable high-speed cruising conditions and activates the metering pump, diesel fuel cannot pass through the blocked nozzle. Without fuel reaching the catalytic converter, the temperature fails to reach the 1,112 degree Fahrenheit target. The module aborts the regeneration, sets P246B, and temporarily limits engine output.
Tests for this include a vaporiser fuel passage flow and pressure restriction check, followed by an auxiliary DPF fuel metering pump delivery rate test.
Thermostat dropping coolant temperature
The third cause, ranked at 50 percent probability with medium severity, involves an engine coolant thermostat stuck partially open. The Duratorq 2.0 TDCi engine management calibration enforces strict operating temperature prerequisites before dynamic DPF regeneration is permitted. The engine coolant temperature must consistently maintain at least 158 to 176 degrees Fahrenheit (70 to 80 degrees Celsius).
If the wax-element thermostat has become weak or mechanically stuck partially open, the engine may reach near-normal temperature in low-speed city driving. Once the vehicle enters sustained highway cruising speeds, high airflow across the radiator cools the circulating coolant down below the minimum 158 degree Fahrenheit abort threshold. The module immediately aborts regeneration, logs P246B, and limits turbocharger boost and engine torque.
You can verify this by monitoring live data for engine coolant temperature during steady highway driving, or by performing an infrared thermal gradient test across the upper radiator inlet hose from a cold start.
Damaged sensing hoses or sensor bias
Finally, ranked at 42 percent probability, we look at the DPF differential pressure sensor signal bias or damaged sensing hoses. The differential pressure sensor monitors the pressure drop across the internal particulate filter substrate using two rubber and silicone sensing hoses. On the Kuga Mk2, these flexible hoses are subject to extreme heat cycles, road grime, and vibration. This makes them prone to splitting, cracking, softening, or kinking.
Internal sensor piezo-element calibration drift can also occur. If a sample hose is leaking, or the sensor has an internal voltage offset, the module measures an implausible or erratic pressure delta during sustained highway loads. Unwilling to initiate regeneration on unreliable backpressure data, the module sets P246B and drops the vehicle into a restricted-power state.
Verify this with a key-on engine-off zero-point calibration reading verification on your scan tool, followed by a pneumatic smoke test and physical inspection of the rubber sensing lines.
Next steps in the bay
When diagnosing P246B on this platform, the exhaust fuel vaporiser system is the logical place to start testing before assuming the DPF itself has failed.
