dpf sensor The The DPF differential pressure sensor is usually mounted in the engine compartment to protect it from heat. The sensor is connected to the engine control unit (ECU) by an electrical connector and connected to the DPF via two silicon hoses. One hose connects before (upstream) the DPF, the other connects after (downstream) the filter. By measuring and comparing the difference in pressure of the exhaust gas before and after the filter, the sensor can estimate the amount of DPM that is trapped in the filter and signal the PCM to start the DPF regeneration process.