I have an 03 plate Audi A4 2.5 V6 TDi (engine code BFC) with a harsh diesel knock & intermittent poor performance. Using the Launch & Snappy I have gotten the code ... 00542 Needle Lift Sensor G80 (sporadic: short circuit to earth)
Anyway I have checked resistance at the plug to the sensor (635 Ohms). I have a 12 volt feed down one of the two wires. It all looks a bit messy on the scope & its hard to see if what I am seeing is a signal or just noise. I scoped the MAF at WOT & it barely achieved 4.0 volts, but I am not convinced this is the cause of the poor performance.
A new sensor is £250 plus Vat (crap discount too ) & fitting it is not straightforward, so accurate diagnosis is vital. I have searched many archives & there does seem to be a lot of wiring issues on these sensors on varying models.
Does anyone have any reference material about how these lift sensors work & even better some test info. I have trawlled through Elsawin, but it doesnt cover this too well. It suggests that the resistance between the sensor terminals should be 80....120w (it looks like a rounded off W on screen) I think it must mean Ohms.
Just to add another angle to the diagnosis, there was also another code 00575 intake manifold pressure (sporadic: resulting limit not reached). This code has cleared.