2005 Audi A4 temperature reading is way low and it's causing the heat to come on when it's hot outside.

Ya ur on the right track..also a loose ground can do that

code p3081 refers to engine temperature too low===causes--allow engine to warm up---cooling system fault
I would check for a thermostat stuck open

code p0322 refers to crank shaft position (CKP) sensor/engine speed (RPM) sensor--no signal===causes--wiring---CKP/RPM sensor---ECM

Checking the pressure with the system not working won't tell you anything. A system with just a half pound of freon will read outside air temp on both gauges with the compressor off.
I guess my first few questions would be - - is the compressor running at idle, what are the gauge readings at idle, and is the cooling fan running at idle ?
The two gauge readings at idle with the compressor running should be 30-45 low and 200-250 high.

You need to diagnose to find out what is CAUSING the coolant error. I cannot tell you what is causing it without diagnosis being performed and although many uneducated peope may try to "guess", neither can they tell you for with any certainty. Diagnosis begins with many questions that must be answered:

> Is the engine running too hot?
> Is the engine running too cold?
> Is there a malfunction in the engine coolant temperature sensor circuits?
> Is the data from the sensor within its designed parameters?
> Is the sensor providing the correct temperature reading to the computer? Or if not, is the reading too high or too low?
> Is the thermostat opening at the correct temperature?
> Etc. Etc..

Replace bad Engine Coolant Temperature (ECT) sensor. That's all the job. Good Luck!

You likely have low coolant causing a large air pocket. This will cause the sensor to pick up the hot steam but the lack of flow through the heater core will not heat up the interior.

vent the hot water system.....undo the highest hot hose clip to vent air,if problem persists then replace thermostat.

There are four sensors for ambient tempurature and they work in unison to provide information to the temp reading on the dash, the heater control head ( where to direct air, blending of warm/cold/outside/inside air flapper controls) depending on the ambient temp and the inside air temp sensor located just above the radio as well as the sun sensor on the top of the dash as well as the a/c compressor head.

When you start your car, the body control module takes the readings from all sensors, outside air temp located in front of the radiator, air temp sensor located in the airbox ( senses temp of air being drawn in from the outside into the air box), coolant temp, inside air temp sensor and the sun sensor on top of the dash (this is why it takes a few seconds for the climate control system to begine when you start the car). The intake air sensor is 1st priority, inside air second, coolant third, ambient 4th and sun 5th. For instance, if the sun sensor reads the sun is hot but the interior sensor reads cold, the inside akes priority. The goal is for the system to achieve a tempurature inside the car that matches the selected temp. It uses all of the sensors to set the system up to achieve that goal as quickly as possible.

Example; Its mid afternoon, sunny and 40 degrees outside adn your in stop and go traffic. The intake sensor reads 40 degrees, the outside sensor reads 60 degrees (heat from radiator...engine heat protrudes into cabin) and the sun sensor reads high (sun is strong). The system is set for 72. priority one sensor reads 40, inside sensor reads 65, ambient reads 60= system will blow hot air to the floor out put, dash outlets will lightly flow 65 degree air so the sun doesnt roast you yet your feet are cold(if it blew hot air from all outlets, your upper body would be hot but your legs/feet would be cold). as the interior sensor reaches desired temp, air will be distrubuted through thee dash, defrost and floor with the warmest air coming out the floor and defrost, coolest air out the dash vents. Its a complex system!

The two sensors that will screw the system up the most are the intake and interior sensors. the system will function reasonably well with just those two sensors though it wont blend air temps between outlets if the sun sensor isnt working. If the outside sensor fails, it simply uses the intake sensor, if the intake sensor fails it will rely on the front sensor. However, since the intake takes priority over the outside sensor, if the intake sensor sends incorrect resistance info rather than failing, it will take priority and cause the unit to malfunction such as in your case.

The intake air sensor can be changed from the outside with patience. If it where me, I would pay the two hrs labor and let the dealer do it right.

Kevin,
Kevins Small Engine service,
South Berwick ME. 03908

Say Eliz make sure your radiator is full of antifreeze and make sure your over flow is at proper level.. If your low on fluid at all the heater will not get hot water to it to work properly .. this is a good start if it has been working in the past ... and thanks jerry

My 2002 Audi A4 doesn't produce the hot air, It's an Auto computer control temperature system. I took my car to the local mechanic (gas station), he said that the water pump and the timing belt need to be replaced.

The heating system normally produces by the engine, then normally the "thermostat' is causing the issue, but the temperature gauge doesn't indicate the overheat.

Any idea what's cause this problem?