Radiator Fan on Full Blast

[A4TUNE]

When I start my car and it stays like that. Keeps the temp gauge between 1/4 and 1/2. I did some reading and it seemed the coolant temp sensor might be the culprit but I replaced that and it still does it. any ideas?

[MikeWire]

Thermostat stuck open possibly? I don't know of any other sensor, but have you scanned the car for codes?

[A4TUNE]

no its not throwing any codes.

anyone?

[old guy]

no its not throwing any codes.

anyone?

There are two coolant temperature sensors. The one you replaced at the back of the block is a 4 pin (dual purpose) sensor. It sends a signal to the temperature gauge and it sends a signal to the ECM for fueling adjustments. There is also a 2 pin temperature sensor in the lower radiator hose. This one sends a signal to the fan control module that activates the cooling fans. Sounds like that one may be your problem. Another possibility is a problem with the fan control module. but if you aren't getting any codes I would start with the 2 pin sensor.

[jcg05c]

ETA fixed my coolent temp guage and my thermometer(how ever you spell that) one when out and then made the other go out also

[A4TUNE]

There are two coolant temperature sensors. The one you replaced at the back of the block is a 4 pin (dual purpose) sensor. It sends a signal to the temperature gauge and it sends a signal to the ECM for fueling adjustments. There is also a 2 pin temperature sensor in the lower radiator hose. This one sends a signal to the fan control module that activates the cooling fans. Sounds like that one may be your problem. Another possibility is a problem with the fan control module. but if you aren't getting any codes I would start with the 2 pin sensor.

is the lower radiator hose sensor you're talking about the one that you remove to change your coolant?

[old guy]

is the lower radiator hose sensor you're talking about the one that you remove to change your coolant?

Correct.

[A4TUNE]

am i looking for the sender or the sensor? guy says the sender is 2 pin and sensor is 4.

[old guy]

am i looking for the sender or the sensor? guy says the sender is 2 pin and sensor is 4.

2 pin. Refer to post #4.

[A4TUNE]

There are two coolant temperature sensors. The one you replaced at the back of the block is a 4 pin (dual purpose) sensor. It sends a signal to the temperature gauge and it sends a signal to the ECM for fueling adjustments. There is also a 2 pin temperature sensor in the lower radiator hose. This one sends a signal to the fan control module that activates the cooling fans. Sounds like that one may be your problem. Another possibility is a problem with the fan control module. but if you aren't getting any codes I would start with the 2 pin sensor.

sorry to be persistent with my questions but when i called the audi parts dept. the guy told me there were two parts in question, one was the 2 pin "sender" which i'm guessing is the one you're talking about which sends the signal to the fan control. the other is the sensor which is the part i think is the flange u take out to empty your coolant. just to be sure, which am i looking at replacing?

[Redgoat]

well... apparently you are looking for the sender.. aka 2 pin

[nikkobdenis]

I have noticed the same thing going on with my car lately. I need to check on the 2 pin sensor. Anyone have a part number?

[Redgoat]

I believe its 06A919501A

[old guy]

sorry to be persistent with my questions but when i called the audi parts dept. the guy told me there were two parts in question, one was the 2 pin "sender" which i'm guessing is the one you're talking about which sends the signal to the fan control. the other is the sensor which is the part i think is the flange u take out to empty your coolant. just to be sure, which am i looking at replacing?

Sounds like the parts guy is either an idiot or he is just being a dick. Tell him to look at ETKA for the 2 pin G2 temperature sensor (as per the Bentley) that plugs into the lower radiator hose. The 4 pin one at the back of the block is the G62 sensor that you have already replaced.

[nikkobdenis]

I believe its 06A919501A

Awesome thanks!

[A4TUNE]

Sounds like the parts guy is either an idiot or he is just being a dick. Tell him to look at ETKA for the 2 pin G2 temperature sensor (as per the Bentley) that plugs into the lower radiator hose. The 4 pin one at the back of the block is the G62 sensor that you have already replaced.

thanks for clearing that up!

[mattman]

could any of the above mentioned possibilities result in a CEL?

[texasboy21]

haha maybe you have one of those awesome ebay "chips!"

JUst kidding sorry I couldnt help more

[diagnosticator]

When I start my car and it stays like that. Keeps the temp gauge between 1/4 and 1/2. I did some reading and it seemed the coolant temp sensor might be the culprit but I replaced that and it still does it. any ideas?

Visually check the inside of the ECU box for water accumulation from a leak. This is the key clues that there may be water inside the box and shorting the fan power supply relay.

[A4TUNE]

i replaced the two sensors and it didn't help.. i also just got a CEL yesterday, the code is

P2181 Engine Cooling System Performance

obviously. going to check the ecu box for leaks tomorrow. any other ideas?

[diagnosticator]

I never thought it would happen to me, but several days ago, the alarm started sounding off then stopping on it's own repeatedly. When I when out to investigate, I noticed the rad fan starting to run then stopping before it got up to speed, cycling like this, so I pulled the negative battery cable until I could check the ECU box for water inside.

When I pulled the cover on the ECU box, sure enough, there was water inside the box with the relays 1/2 submerged. I was able to salvage 1 of the relays, but the other two where beyond hope, requiring replacement with a new relays.

Fortunately the problem had not yet progressed to soaking the carpet and the Central Electric and Convenience Modules.

If your ECU box has water inside, don't forget to find and fix the cause of the water leak. Associated with this is to make sure the plenum drain is not blocked with trash. The drain is under the battery.

[Redgoat]

John, I have the "radiator fans kicking on when they feel like it" problem as well still. I replaced the relays below the ECU (inside the box) but it still continues :(

[old guy]

i replaced the two sensors and it didn't help.. i also just got a CEL yesterday, the code is

P2181 Engine Cooling System Performance

obviously. going to check the ecu box for leaks tomorrow. any other ideas?

Most definitely check the ECU box for water. However, I would be surprised if that is your problem. when the fan control relay gets wet you will get erratic operation as diagnosticator experienced or else the fans will run continuously, even when the car is turned off. If I read you original post correctly yours do not run with the car turned off but run continuously when the car is turned on. I checked the Bentley for code P2181 and it points squarely to a sensor problem, either with the sensor itself or the ECU not getting a signal from the sensor. Another possibility is a problem with the fan control module. Since you have already replaced both sensors that narrows it down a little.

My suggestion is as follows:

Check the ECU box for water.

If it is dry you need to purchase a manual or take it to a shop. You can certainly trouble shoot yourself but you will need to increase your information source to continue. For example the Bentley gives you all the information necessary to check out the sensors, wiring and ECU outputs that control the fans. but it requires removing the ECU and knowing what pins to check for output, continuity etc. The one time cost of the manual will be cheaper than one trip to the shop.

Here is a little more info on how the temperature sensors work with the ECU to control the fans:




Engine Coolant Temperature (ECT)
Sensor G62 and Engine Coolant
Temperature (ECT) Sensor
(On Radiator) G83

These sensors both operate as negative
temperature coefficient (NTC) sensors. The
coolant temperature set points are stored in
the Motronic Engine Control Module J220
in the form of maps.

The actual coolant temperature values
are registered at two different points in
the cooling circuit and indicated to the
Motronic Engine Control Module J220 in
the form of a voltage signal.

* Coolant actual value 1 is measured at
the cylinder head coolant outlet by
Engine Coolant Temperature (ECT)
Sensor G62 located in the upper level of
the coolant distributor housing.
* Coolant actual value 2 is measured at
the radiator by Engine Coolant
Temperature (ECT) Sensor (On Radiator)
G83 before the radiator coolant outlet.

Signal Utilization

Comparison of the specified temperatures
stored in the maps with the coolant actual
value 1 temperature gives the pulse-width modulated signal for the application of
voltage to the heating resistor in the Map
Controlled Engine Cooling Thermostat F265.
Comparison of the coolant actual values
1 and 2 is the basis for activation of
the electric Coolant Fan V7 and Coolant
Fan -2- V177.

Effects of Failure

If Engine Coolant Temperature (ECT)
Sensor G62 fails, a defined substitute value
of 203°F (95°C) is used for coolant
temperature control and the first fan speed
stays activated.

If Engine Coolant Temperature (ECT)
Sensor (On Radiator) G83 fails, the control
function remains active and the first fan
speed stays activated.

If a certain temperature threshold is
exceeded, the second fan speed is
activated.

If both sensors fail, maximum voltage is
applied to the heating resistor in the Map
Controlled Engine Cooling Thermostat F265
and the second fan speed stays activated"

Good luck!

[A4TUNE]

well i haven't got it fixed yet but now the fans have completely stopped. my appointment isn't till tuesday.. can i drive my car till then, the temp gauge now stays at the middle and doesn't overheat.

[nikkobdenis]

well i haven't got it fixed yet but now the fans have completely stopped. my appointment isn't till tuesday.. can i drive my car till then, the temp gauge now stays at the middle and doesn't overheat.

Sounds like it is running correctly now, just watch for overheating at stoplights.

[A4TUNE]

well i still have the CEL for engine cooling and the fans don't seem to be working at all.. i know this because after a 20 min drive i stopped the car and popped the hood and they weren't turning..

[j-rod]

Whatever became of this?

My fan comes on full blast only on a cold start and stays on for a few miles then stops. I'm also getting the P2181 Cooling Malfunction code.

[MikeWire]

P2181 refers to the ECT sensor G2 at the back of the block. You can test it - the procedure basically says to jump terminals 1 & 2 (there is a diagram if needed) and replace the sensor if your scan temps are reading +140C. Remove the jumper wire, and replace if the scan temps are -40C. If that doesn't work then move to the ECU and test.

So basically just replace the sensor and clear your codes. It's easier and takes less time.

[diagnosticator]

well i still have the CEL for engine cooling and the fans don't seem to be working at all.. i know this because after a 20 min drive i stopped the car and popped the hood and they weren't turning..

The fans usually are not running while driving because the forward motion of the car provides for the air flow through the radiator core. The fan runs if the car is not moving much like in a traffic jamb or long lights etc.