Outside air temp sensor

hothatch2002 · Nov 15, 2005

I have noticed that my car has an external air temp sensor in front of the drivers side air intake duct for the engine rad.

Is this function of this sensor to inform the engine management of the ambient air temp or is it simply the sensor to inform the driver of the external temp and display it below the rev counter.

The reason I ask this is because I have the sensor mounted on the car, but do not have a disp belowthe rev counter showing me what the external temperature is. Was it an option for external temperature display or standard on all models. Mine is a 98 C4 by the way.

Rotorhead · Nov 15, 2005

I thought that it was the external temp sensor.

The display is part of the on-board computer option, I think.

THX911 · Nov 15, 2005

For your year, I believe you need the on-board computer (OBC) to display it. There are sites out there which show you how to hack the car to show this display and other OBC data; I don't think it is trivial though...

Edited to add:
The sensor is used by other things too; the other option I know which uses it is the automatic climate control...

Richard_Hamilton · Nov 15, 2005

The OBC has to be activated with a Porsche System Tester 2. Once it has been activated (without doing any of the rest of the hack) it will display outside temperature in the rev counter.

The hack isn't terribly difficult for the DIY'er, but you can get it done here for £100 - http://www.wrightune.co.uk

Mark_Bennett · Nov 15, 2005

They all have the sensor.
My Box S has one - and I was too cheap to get the OBC...[

]

Guest · Nov 15, 2005

I believe it is primarily to show the external temperature.

However, remember that the compressor for the air con is switched off if the air temp is below 3 deg C (since it can't cool the air much more, the air is generally not very damp, and the air con rad will ice up). I guess it is fitted to all cars since they all have air con, so it is necessary for this function too.

Paul Fraser · Nov 15, 2005

I don't think that Boxsters without aircon have this sensor and those with do: therefore I think it is aircon related.

I suggest you do what I did and get your OBC (On board computer) turned on by the OPC at your next service. This cost me nothing when I recently had a minor on my Boxster. After all they have the PST2 on it to read any fault codes anyway, and it takes two minutes. I recently asked for screen shots on Renntech

http://www.renntech.org/forums/index.php?showtopic=6931&hl=

to take in with me as some OPCs are completely clueless when it comes to doing this (this was my third attempt over the 996 and Boxster, or maybe they just couldn't be a***d).

You may want to ask again on Renntech -- Loren is very helpful -- with your car type and year as I think there are some differences (maybe not in enabling it but certainly in display -- off the top of my head there is some dot-matrix/non-dot matrix stuff with later Boxster models). Hope this helps.

Richard_Hamilton · Nov 16, 2005

I THINK the outside air temperature sensor at the front of the car is purely for the OBC. According to the air conditioning section of the workshop manual the outside air temperature sensor is in the ducting in the footwell:

"Removing and installing outside temperature sensor on the installed heating/air-conditioning unit:
Removal
1. Remove footwell bulkhead and right air guide. Remove drive motor for fresh-air/recirculation valve.
2. Pull off electrical plug connection on the outside temperature sensor. Turn temperature sensor by 90° and pull it out."

I think it samples the air as it goes into the system.

Paul Fraser · Nov 16, 2005

Interesting: I wonder why the sensor would be fitted as a matter of course to non-OBC cars? Any ideas?

Tool Pants · Nov 17, 2005

I can tell you what I have seen and what I have been told. At least for an early 986 US car.

Aircon has always been standard in the US. The very early 986s did not have the sensor unless the car had the OBC option. These were model year 1997 (the first year for the Boxster) that were built in 1996 for model year 1997.

We have 2 local model year 1997 owners and their cars were built in November and December 1996 without the OBC option. Both have aircon because that is standard in the US, but neither have the outside air temp sensor in the front grill. My model year 1997 was made in January 1997. I have aircon because that is standard, but I also have the sensor even though I do not have the OBC option. So I have always assumed that a US car made prior to January 1997 did not have the sensor unless the car had the OBC option. All US cars I have seen made in January 1997 and after had the sensor even if the car did not have the OBC option.

About 5 years ago the December 1996 owner wanted to have the outside temp display turned on. When a mechanic I know turned it on all you saw in the instrument cluster was 3 dashes, - - -, because this car did not have the sensor. The mechanic told me we needed to install the sensor. So we installed the sensor and wired it to the instrument cluster, and then he could see the temp display.

The mechanic said he was told by Porsche to install the sensor on the very cars because the aircon system was not working properly without the sensor, or something like that.

I asked the mechanic who turned the display on why this car did not have the sensor, but mine did, as they were otherwise identical cars built a month apart. Again, it had something to do with the aircon.

I would have to look at the wiring diagrams to see if the sensor has anything to do with the aircon. Until then I am just repeating what I was told.

This is a picture of the November 1996 car.

hothatch2002 · Nov 17, 2005

How much should the dealer be charging me to activate the outside temp display? My car is booked in for warranty work at the beginning of december, so they could do it then, but I don't want to get robbed by them. (You know what Porsche Dealers are like)

Paul Fraser · Nov 17, 2005

This is a how long is a piece of string question. Ask them and take it from there. It takes five minutes so they might do it for nothing whether or not they have to plug the PST2 into the car for the warranty work. On the other hand they might charge you an hour's labour. You will have to ask them.

Richard_Hamilton · Nov 17, 2005

I checked the wiring diagrams, and the outside air temperature sensor at the front of the car connects directly to the instrument cluster, and the intake air temperature sensor (in the duct in the footwell) connects directly to the climatronic. In the diagnosis section of the manual it states that the instrument cluster provides the heater/aircon system with information such as outside temperature (from the sensor under the bumper), coolant temperature, engine speed etc. So Tool Pants is spot on, and its a total mystery as to why they didn't fit them on early Boxsters.

Hothatch - if you are anywhere near me (Maidenhead) I might be able to help - email me.