Read how a fault in a Ford Focus's diesel particulate filter sensor was diagnosed, repaired and verified using a diagnostic platform from Snap-on.

A 2011 Ford Focus with a 1.6L common rail diesel injection system had the engine management light illuminated and a fault code was retrieved with the aid of a Snap-on VERUS Edge scan tool.

The fault code was:

• P0473: Exhaust gas differential pressure sensor signal – short to positive or open circuit

The most important clue with this fault condition was that the fault would not clear with the ignition on (key on, engine off).

This was indicative of an electrical fault with the circuit. A mechanical fault would have cleared initially but instead it re-appeared when the engine was started.

I began by testing the supply voltage and ground circuit and found that both were functioning correctly.

The next test was to measure the signal voltage, and I measured 4.8 volts on the signal wire from the engine control module.

This was with the sensor plugged in and disconnected.

This voltage is supplied from the control module and the sensor output voltage can “pull” it down depending on output voltage from the sensor.

This explains the fault code’s sub-code: short to positive or open circuit.

I removed the sensor from the vehicle and supplied it with a 5 volt supply and a ground. There was no output voltage from the sensor, indicating the fault.

I received a new sensor and again supplied it with a 5 volt supply and a ground.

This time I measured 0.4 volts on the signal wire and the voltage increased when I applied a positive pressure to the sample pipe which detects the pressure upstream of the filter.

The sensor was fitted to the vehicle and the fault code was cleared with the VERUS Edge. A test drive validated the repair.

The image below shows the DPF sensor during testing the output voltage:

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