2006 Mercedes E350 code 970 or P0452 Evaporative Emissions system pressure sensor low input

Quick tips on diagnosing a shorted fuel tank pressure sensor on a 2006 Mercedes Benz E350. This model has access from under the rear seat with a replaceable fuel tank pressure sensor. On models with a FTPS built into the fuel sending unit and a harness that runs underbody instead of in cab, Mercedes recommends dropping the fuel tank to check for chaffed wires on the harness before condemning the sensor. In this video I’ll show you how to trust your meter and scan tool readings to condemn a malfunctioning sensor. There is one step further than this, and that is not shown in this video, which involves load testing completely isolated individual circuits from the ecm connector all the way to the sensor in instances where a circuit may show an ohm reading in specification, but replacing the condemned sensor does not fix the issue. Remember that if one or two strands of wire in a group are in reasonable condition a circuit may give an appropriate ohm reading, but under load the circuit will fail. Voltage testing is almost always more accurate than resistance testing. In this instance we repair in order of likelihood of failure based on our readings and probable cost to the customer. Replacing the sensor fixed the issue. In this particular case once the evap system restored to operational condition it threw a p0444 code for the purge solenoid which also ended up being faulty. Replacement of both of these components got this customer ready for state inspection.