Getting gray hair with Pioneer ND-PS1 parking sensor problems on the Audi TT

I upgraded the TT's random aftermarket head unit with a Pioneer SPH-10BT 1-din head unit, which has the nice feature of using your phone as an extended display. This is especially useful in a vehicle where there's space only for an old 1-din stereo.

I had bought the head unit, a cute small sub (Pioneer TS-WX130EA) and the parking sensors as a kit a couple of years ago, but had only gotten around to install the stereo and the subwoofer. Now as my son is learning driving, we have been using the Audi TT for training. It is my only stick shift vehicle, plus it is so old that it has a manual handbrake, manual wipers, and manual lights, all useful when learning to drive. Imho.

The sensors are installed in the bumper cover in holes drilled with the provided hole saw. Assuming you measure the drilling correctly, the sensors will install beautifully flush.

The Pioneer ND-PS1 comes in a small box, containing the unit, power cable, data cable, four sensors and cables, zip ties, some velcro and even a 19mm hole saw for drilling holes in the bumper cover. The small, sparse manual explains how to connect the data cable to your head unit, the power cable to the reverse light, and how to install the sensors... but it fails to mention an important thing...

Installing the parking sensors according to the manual WILL NOT WORK. The Pioneer SPH-10BT head unit requires that the purple/white wire in its harness (labelled "REVERSE GEAR SIGNAL INPUT", see pic) needs to be connected to the reverse light signal as well. The manuals overlook this for some reason, and there is no wire provided for this purpose either, even with everything else nicely included.

Installation is not super tricky once you figure out that the purple/white wire needs to be connected, especially if you manage to do this at the same time when routing the data cable. On the other hand, if you do this only after spending time measuring voltages and looking for bad fuses, earths, and what not, it will take quite some time.

Why the connection is not mentioned in the documentation or why there is no wire for it is beyond me, when the package is otherwise fully equipped. For anyone having installed similar devices previously it should be pretty obvious that the head unit needs a signal to go into "reverse mode". This is normal in an installation of e.g. the Chinese reverse cam. However, when everything in the Pioneer ND-PS1 package seems complete and thought out, you would assume they have this figured out and that the reverse signal travels along the cables already provided. But no...

The installation manual for the Pioneer ND-PS1 says the sensors are pre-programmed for a distance of 55-65cm from ground level (but has no mention whether you can change this setting). On the Audi TT, there are not so many options considering the install height. There is a steel bumper bar that ends at about 56cm from ground up, and there's a plastic support grid that starts at around 61cm or so (on a vehicle with factory sport suspension, no aftermarket lowering kit). There is a 5cm slot between these where the sensors will easily fit. I measured the holes at 57cm from ground and they fit nicely. Sideways the sensors are placed with a 40cm interval.

The TT is well sealed and there are only few obvious points for routing cables from the outside into the trunk area. There are two unused plugs on the upper vertical part of the rear panel, on left and right sides of the trunk locking mechanism. To access these, you need to remove the outer bumper cover and the trunk rear interior panel (the big piece of plastic that covers the lock). I taped the cables together with some gorilla tape and the resulting lump fills the entire cavity when stuffed. These are only visible from the outside.

I also removed the trunk floor to feed the data cable and the problem wire underneath the rear seats, to the trunk, and underneath the right side panel. The parking sensor unit I placed inside the right service panel in the trunk side lining.

In use the parking sensors sensitive and appear accurate, with object distances measured up to 10cm intervals (accuracy not checked though). The device warns of objects starting at around 2.5 meters behind the vehicle.

The Pioneer SPH-10BT head unit displays basic info about approaching obstacles, so info is available even if the phone is not connected and open. The only real gripe I have is that it takes a while for the unit to boot up, so parking sensors are not available immediately after starting the car.