Dear Scotty,
Despite your years of good advice I ventured out and got myself a 2017 Mk1 VW Tiguan 2.0 TSI 4Motion made in Wolfsburg, Germany. I believe its one of the last in production before the Mk2 was released. It has 56,000 KMS, all dealership maintenance, one owner. Everything seems to work fine except for the Ambient Air Temp sensor that whenever you drive the car a little harder, say over 3000 rpm, the outside air temperature starts to go up, its in celcius it has reached 53 C (127 F) when outside temp is closer to 80 F. No codes on high level scan tool. Everything else works fine. Replaced sensor already, problem remains. Car has never been crashed. Took the bumper down with mechanic and we're not sure whats causing it to go high like that. Oil temp and coolant temps both ok. Sensor has been replaced with new one, same problem remains. Is it just weird and nothing to worry about or could it be a symptom of some overheating going on in the engine compartment? Thank you
2017 Volkswagen Tiguan 4motion 2.0 TSI with 6 speed automatic transmission
Sounds like the sensor is placed too close to the engine compartment/exhaust plumbing.
No codes on high level scan tool. Everything else works fine.
Weird for a VAG vehicle..
It doesn't sound like a sensor or wiring issue because it doesn't act up unless "you drive the car a little harder, say over 3000 rpm". You said if you drive the car soft it seems to work OK.
The ambient air sensor circuit is easy to test but the voltages are monitored by the PCM and if the voltages were out of range it would have set a circuit code and your guy with his " high level scan tool" would have seen the circuit code.
The ambient air temperature "sensor" is a thermistor. A variable resistor whose resistance changes with temperature.
They all work pretty much the same. The "sensor" has 2 wires going to it. On your VW, one wire provides 5 volts to the "sensor". That 5 volts is called the 5 volt reference and it comes from the Instrument Panel Control Module.
The other wire is the Ground that goes back to the Instrument Panel Control Module.
And I'm pretty sure the voltage is measured on the Ground side on the VW's. That means when it's Cold outside the resistance is lower (the voltage goes up on the Ground side) and when it's Warm out the resistance is higher (so the voltage goes down on the Ground side). Those voltages are converted to a temperature readout on your dashboard.
And I know what you're thinking. "What if this is a battery charging issue making it read a lower voltage?" But if the charging system couldn't even provide 5 volts for this circuit your car wouldn't run.
So to test the circuit you just unplug the connector at the "sensor", hook up a multimeter (DC volts, 20 volt range) to each terminal of the wiring connector, and turn the key to ON. You should see around 5 volts on the multimeter. That means you have no opens or shorts in the wiring from the dash module to the "sensor".
But like I said, you have no codes and the higher temp readings only happens when you put the engine under load. Otherwise the sensor seems to be working OK and that seems to point to it's genuinely picking up a higher temperature at its location when you put the engine under increased load.
The ambient air temp sensor isn't shielded with any insulation and if you changed the sensor already (hopefully OEM) then I'd suspect the sensor is honestly picking up heat from the Radiator or AC Condenser.
Since it happens under engine load that points to the radiator.
I'd wonder if my cooling fans were kicking on to high speed, or if I had an obstruction in the radiator, or my radiator fins were crudded up, or a sticky thermostat that isn't opening all the way, maybe even the water pump (I've seen the fins on a water pump eroded down to nubs). Something along those lines. Just because you're able to maintain good engine coolant temperature doesn't mean that these components are working optimally.
Seems like an electric problem. Start simple:
1. Is your battery and alternator working properly?
2. Check the wiring, is there any visible damage? Also check with a multimeter for short/open circuit.
3. If the sensor is good, the wiring is good and the power supply is good, it could be a faulty HVAC control module but that seems very odd. (Also not worth replacing for this problem unless under warranty)
Is it just weird and nothing to worry about or could it be a symptom of some overheating going on in the engine compartment?
Question: When it starts to show excessively high temperature, does it immediately go down as you let off the throttle (faulty data/electrical issue)? Or does it stay for a couple of minutes? Maybe there is a dense amount of heat in a very specific area (aka the location of your sensor) when there shouldn't. (missing heat shield, etc.) That is a possibility.
Last question: If you drive softly and let the engine reach it's normal temperature, will the problem show?
Hi, battery is brand new, alternator is working fine AFAIK.
AS far as there being no codes, I found it weird myself, I half expected to have a very scary experience but all that showed up was some rear foglight lamp code that the mechanic cleared. They did run the whole scan (mind you this was at a regular mechanic, not the dealership, but the man has a GTI himself).
The temperature stays high for a while, it doesn't seem to be random data, it seems it does get hot in there. So its located behind the front bumper on the driver side. We took the bumper down and replaced it in the same postion where it was. If there's some insulation missing its a possibility, I'm not really sure. It was a used car and theres bits and bobs missing here and there, say the first aid kit is nowhere to be found, and ther';s minor cosmetic stuff.
IF one drives it soft, the temp seems to be correct until there's harder accelaration. If driven on flat terrain (I live in a hilly place) you can be 5-10-15-20 minutes even and the temperature is normal. If you accelerate hard it will start to go up and going fast uphill is when it gets to very high numbers. Highest I've seen is 53 C. During this whole time the water temp stays right at 90, but I understand in volkswagens it does not really correlate with engine temperature.
It drives well, feels fine, but it drives me crazy to see on the corner of my eye hey its 47 C when its 25 outside.
Some missing heat shield is possible.
IT really seems to happen when going uphill at higher RPMs. I'd say in normal driving Its gotten up to 45 C when in a hilly area. If I'm going flat it stays accurate to the outside weather. There's obviously a delay and goes up in increments. It doesnt suddenly get all hot, starts going up and up 30 C then 31.5 accelarate more soon its 35, then 37 and so on, its gradual and to me its getting hot in there.
Is the sensor in the correct spot? I have to assume it came from the factory that way but as with any used vehicle one doesn't really know
Assuming the one who replaced it is working as it should, easiest fix is to try and move it elsewhere, just a temporary spot with zip ties to see if it goes away.
If it changed nothing: it's picking up the heat of the engine bay, not much to do. Continue for potential electrical problems (less likely):
You mention a lot of uphill situations:
-Could be that the sensor is not properly seated
-Could be that the wiring is not properly seated/protected
-As you accelerate hard, the engine moves a bit, could be that a wire close to the engine is getting eaten up by a piece of the engine everytime it "moves", double check the wires) (As you go uphill, everything moves a bit too)
- It could also be a loose connector
-**Both of these causes could cause higher resistance in the circuit (higher temperature reading) but not enough to trigger a code.
Let us know what it changes.