Along with a new set of tires, I decided to install a Hella TC-400 tire pressure monitoring system (TPMS). For reference, another board member installed a system made by Orange Electronics (see http://www.renntech....ms-check-it-out).
[Edit 12/9/2018: For sensor replacement, scroll down towards the end.]
This TPMS installation was for my particular 2003 986S. Other vehicles may be different, part numbers change, and there are safety risks involved in doing mechanical and/or electrical work on a vehicle. What's presented here is a general overview of my DIY project, not a complete step-by-step set of instructions. Please obtain, understand, and follow the necessary repair and installation procedures in order to work safely, avoid damaging anything, and achieve a safe result.
The Hella TC-400 TPMS uses valve-mounted sensors that wirelessly transmit the pressure and temperature information to a hidden receiver that is wired to the remote display unit. Unless you have the proper tools and training, you need to have the sensors installed by a tire service professional.
I first made sure the key was out of the ignition and then disconnected the battery. I removed the lower center console, the center console-delete trim, and the glove box.
I installed the receiver on the firewall-side of the HVAC/fan housing. I decided on this location to keep it sufficiently away from airbags and other sensitive devices. The receiver has two large tabs that can be used for mounting, but I cut them off and smoothed them over with a rotary tool. The Hella kit comes with double-sided mounting tape that I used to mount the receiver to the HVAC/fan housing. The receiver is light and the tape makes a very strong connection—clean the surfaces with naphtha (or some other cleaner/degreaser) before affixing the tape. In the photo below, the view is upward from the passenger footwell. (The labeling on the receiver was added by me.) The single, black wire is the antenna (it is about 30 cm long) that I merely stretched out and laid along the top of the carpeting, extending towards the passenger door.
There are two sets of wiring that connect to the receiver. The first is for power and ground connections, and the second is wiring for the display unit. I bundled both sets of wiring together in black plastic spiral protective wrapping. This wiring harness extends from the receiver, along the underside of the HVAC/fan housing, up the same housing, and then heads over to the center of the dash. The photo below is taken with the glove box removed.
I routed the wiring harness through the framing of the center console where I made two connections:
A. For the connection to the display unit, I cut the Hella wiring and added a 3-pin male/female Molex connector (available at your local electronics store) in order to facilitate installation/removal of the console-delete carpet trim that the display unit is mounted to.
B. For the power connection, I used the phone prep connector. For additional reference seehttp://www.renntech....stery-connector and http://www.renntech....-interier-parts. To connect directly to the phone prep plug, you need the following Porsche parts:
(1) each -- 999.652.758.40 -- plug socket, 4-pin, female
(3) each -- 999.652.570.22 -- pins/connectors
These parts are inexpensive, but needed to be ordered from Germany, which only took an extra week or so by ordinary delivery methods. I bought extra pin contacts in case I messed up during crimping/soldering. I think the phone prep wiring is a good choice for this application because it has the required constant and switched power (both are fused) and ground connections (thus, I did not install the fuse that came with the Hella kit).
For my car, the phone prep wiring corresponded to the Hella wiring as follows:
Term. 15 (pin 2) Green w/Black stripe >>>>> Hella Orange
Term. 31 (pin 4) Brown >>>>> Hella Black
Do not connect to pin 3 in the phone prep connector (it is for the telephone mute).
As you can see in the photos below, both connections are established in front of the shifter assembly away from airbag control module. Porsche specifically advises not to "locate plug in the immediate vicinity" of this module. I wrapped the connectors together with felt tape to prevent rattling/noise.
The display unit is simply affixed with Velcro tape to the carpeting. A carefully drilled hole through the plastic backing of the carpet/cover serves as a pass-through for the wiring.
The finished installation looks as below. The display lighting can be changed. I selected something that is very close to the other dashboard lighting—the photo gives you some idea (it matches better in reality). The display is only lit at start up or if you press the "check" button. Of course, it is lit (in a different color) when there is a warning.
The system self-check indicated maximum signal strength from the tire sensors. To set the system, you need to accurately set the tire pressures after the vehicle has been sitting at rest for at least a few hours and perform a few button presses per the instructions.
If you quickly press the "check" button, the display cycles through each tire, showing the pressure and temperature. At the moment I snapped the photo above, the unit was displaying the temperature of one of the tires. You can press the "check" button repeatedly to show data for any tire you want. After a minute of inactivity, the display dims.
I like having the peace of mind for the operating condition of the tires, the prevention of damage to a wheel (from a flat), and for safety's sake (of course).
Edit 12/9/2018: Replacement Sensors for Hella TC-400
It’s been about 8 years since my installation of the Hella TPMS and needing new tires prompted me to look into replacement pressure sensors. The TC-400 system does not seem to be currently marketed, and what Hella products I could find online were minimal and appeared to be new-old-stock. With some TPMS knowledge and use of a diagnostic tool I was able to determine through a little trial and error what ‘fresh’ sensors on the market today would work with the Hella TC-400.
This is an original equipment sensor used in many vehicles in the early/mid 2000’s. I tested it and it is a drop-in replacement for the Hella TC-400. Simply install in the tire/wheel assembly and run the reprogramming and pressure setting procedures in the TC-400 manual. The advantage to this sensor is that it will work out of the box; the disadvantage is a more substantial cost per unit.
Alligator Sens.it Programmable Sensor 590883 (433.92 MHz):
Alligator is a German company in the valve component business. Programmable sensors are more commonly found on the market since they can be used with a wide variety of vehicles with different TPMS technology. These sensors can be much less expensive than OE components, but they require specialized hardware or a TPMS diagnostic tool to program. With that hardware, the user selects the vehicle model the sensor is for, and then the sensor is wirelessly activated and assigned to that vehicle type. Some vehicles will require additional steps to recognize the sensors once programming is complete. I installed four of these sensors with a new tire change and they work flawlessly with the TC-400 already in my car. I programmed them to a 2003 BMW 3-Series E46 (other vehicles may work, including 2005 Boxster, but I had more complete information about the BMW system when I began my research). After programming the sensors, I ran the reprogramming and pressure setting procedures in the TC-400 manual.
Other sensors may work, including programmable sensors by Schrader, but I simply did not evaluate or test any others to be sure.