ghibliss

My 2004 A8L ambient air temperature gauge has recently been reading quite a bit higher then normal. It is showing deviation of close to +20 degrees which obviously is incorrect. The J255 LCD display has always been quite accurate showing the temperature within a few degrees of the outside temperature.

I replaced the G17 sensor located in front of the radiator and am still getting bad data on the display. I read the schematics for this and it shows the sensor connected directly via the wiring harness to the J255 panel in the instrument cluster. I checked the resistance of the harness from the sensor to the instrument panel and it is within specification as it is extremely low (spec. is .35 ohms or less)per the schematics.

Has anyone encountered this issue and had a successful resolution to the problem? The only other thing to change is the G89 sensor which is the fresh air intake sensor located under the pollen filter near the firewall of the car. The system displays the lower value of the two sensors on the LCD display so it is entirely possible that we simply replaced the wrong sensor this time around. I doubt that since the display is showing a temperature albeit higher then normal that anything is wrong with the instrument panel.

There are no error codes being shown which I would have expected to see 00779 outside air temperature sensor for G17 or 00787 which is for the fresh air intake duct temperature G89. Neither of these codes has appeared nor anything else related to the sensors.

I will be testing / replacing the G89 sensor this week to see if that corrects the problem. If we disconnect the G89 sensor and there is no change in the displayed value on the LCD panel then it is likely it simply needs to be replaced as it would be then showing us the G17 sensor reading. Could the Climatronic control module need to be recoded?

Any assistance regarding this problem would be greatly appreciated!

ghibliss

My 2004 A8L ambient air temperature gauge has recently been reading quite a bit higher then normal. It is showing deviation of close to +20 degrees which obviously is incorrect. The J255 LCD display has always been quite accurate showing the temperature within a few degrees of the outside temperature.

I replaced the G17 sensor located in front of the radiator and am still getting bad data on the display. I read the schematics for this and it shows the sensor connected directly via the wiring harness to the J255 panel in the instrument cluster. I checked the resistance of the harness from the sensor to the instrument panel and it is within specification as it is extremely low (spec. is .35 ohms or less)per the schematics.

Has anyone encountered this issue and had a successful resolution to the problem? The only other thing to change is the G89 sensor which is the fresh air intake sensor located under the pollen filter near the firewall of the car. The system displays the lower value of the two sensors on the LCD display so it is entirely possible that we simply replaced the wrong sensor this time around. I doubt that since the display is showing a temperature albeit higher then normal that anything is wrong with the instrument panel.

There are no error codes being shown which I would have expected to see 00779 outside air temperature sensor for G17 or 00787 which is for the fresh air intake duct temperature G89. Neither of these codes has appeared nor anything else related to the sensors.

I will be testing / replacing the G89 sensor this week to see if that corrects the problem. If we disconnect the G89 sensor and there is no change in the displayed value on the LCD panel then it is likely it simply needs to be replaced as it would be then showing us the G17 sensor reading. Could the Climatronic control module need to be recoded?

Any assistance regarding this problem would be greatly appreciated!

mishar

If the system displays the lower value of the two sensors and you are getting higher reading than it is not sensor (unless both of them are faulty). I do not have that problem (yet ) but have few problems with harnesses. Contacts are less than perfect so low voltage signals are interrupted. That would bring all kind of errors like airbags, ESP, navigation and so on. Way to deal with that is to clean contacts and apply some contact improving staff. I've just ordered CAIG DeOxIT Liquid. I hope it will help.

ghibliss

I have replaced only the G17 ambient air temperature sensor which provided no change in the readings. This tells me that there was nothing wrong with this sensor and that I most likely changed the wrong part causing the problem. The sensor comes with the cable to connect to the harness and the two pin connector to the harness was perfectly clean and had no oxidation which would cause the problem which you noted.

I will report my findings later this week after I replace the fresh air intake sensor. If this sensor has failed (as in completely dead) then the system is only displaying the results of one working sensor and not the lower value of the two in the circuit.

mishar

If it is displaying the results of one working sensor and that one is good than you would have accurate reading. If the fresh air intake sensor is completely faulty you should have engine errors.

I believe there are few harnesses between sensor and module. Any one can be a bit rusty. Probably not noticeable but enough for that low power signal to be distorted.

MP4.2+6.0

so shouldn't throw engine codes.

For OP, I haven't run into this w/ an Audi since they were put into the C3. Had one physically damaged on a Chrysler (down low in front of radiator; not that different than Audi's). If there is a second one up by the HVAC filter, then I suppose it could be electronically bad (not likely to be physically damaged there). Since that air draw doesn't involve the engine area/heat, if anything I would think it would be less vulnerable to heat soak and thus a faulty reading, at least while driving. Also, any chance the measuring blocks can be read for the sensors like they can for a variety of other components? If so, you could obviously see an implausible reading. Finally, to your original post, unless you did something to alter the coding, I wouldn't expect anything amiss there. In general, the various computer/control boxes are not vulnerable to somehow losing their coding already in place.

mishar

You are right. But simple logic stays that if one of two sensors is good, since the system is displaying lower of two values, getting high reading can't be caused by faulty sensor.