engine coolant temp sensor mismatch Wiring experts help!

[okar]

1999 Audi A$ Quattro Is it possible to run a 3 pin temp sensor to the 4 wires coming from the harness. ?

please be patient, this has become my problem passed on by p.o. temp gauge was not moving on first road trip, which led me to the present.

Other than switch radiators, and buy one that takes the 4 pin type, which is the obvious and more expensive choice... Is it possible to not use one of the 4 wires.?

I understand that they signal a hi and low fan speed, but I am not sure which does which. seems that the red with brown is high or constant power?
4 wires coming from harness:

1. red with brown tracer

2. brown solid

3. brown with green tracer

4. brown with yellow tracer

3 pin connector has 1. brown with black, 2. red with brown, 3. brown solid. what is the function of each wire color?
Bentley manual only gives color of 3 wires on the diagram and was not much help. Unless I am missing something.


please help

Okar

[okar]

bump

[walky_talky20]

Yes, this is very doable. There are just 2 grounds on the 4-pin version and a single ground on the 3-pin.

Brown and Brown/Yellow are the grounds. Test with a meter to be sure, though. Hook ground to pin #3 on your switch.

Brown/Green is Cooling Fan Relay (Low Speed). Hook this to pin #2 on your switch.

Red/Green is Cooling Fan Relay (Hi Speed). Hook this to pin #1 on your switch.

The switch is merely applying ground to each of those relays. If you use a meter to check the Brown/Green and Red/Green wires, you should see ~12volts that leaks through the relay coil. That's not 12 volts to the switch, it's just indicating there is 12 volts on the other side of the relay coil. Apply ground to that and then the relay will close.

[okar]

Thanks for the reply, I mis-spoke. This is the coolant fan control switch on the lower corner of the radiator .

I was worried before
but the C FC thermal switch just runs the viscous fan.

Thanks again!
I can set this up after work

[okar]

Ok. Walkie, I got the actual Engine control temp sensor, swapped, bought a chinese one first. because audi dealer put me on a long hold, I should have waited!
the chinese one had no O ring, so I used the old o ring. mistake # 2.

on the way home last night the car was herking and jerking, and died once or twice. so today on the way back to the shop I realized that i had a leak, shop filled up with smoke from the leak.. I called dealer and got the oem sensor and o ring. this time it took me 3 minutes to swap.
the problem is that after installing and bleeding the system correctly the i get a stumble on the throttle. I cleaned the MAF sensor and it was a bit better but still the stumble on throttle.
I tried resetting the throttle body with ross tech, and i got an "error" what gives? the car was running great before all of this temp sensor stuff.

[ricekikr]

on the way home last night the car was herking and jerking, and died once or twice. so today on the way back to the shop I realized that i had a leak, shop filled up with smoke from the leak..

Overheat? Does it still smoke? If yes, possible headgasket, warped head. Compression check.

[walky_talky20]

I have no idea what is going on in this thread.

Part 1: How do I wire a 3 pin thermal fan switch to the 4-wire harness?
Part 2: I explain how to do this
Part 3: Something about the viscous clutch fan?
Part 4: Now we're talking about the coolant temp sensor. ?? I don't know why either.
Part 5: Hold music? And then something about chinese parts.
Part 6: Now something is smoking and there is talk of cleaning the MAF and resetting the throttle body.

I am completely lost after step 2.

[okar]

I have no idea what is going on in this thread.

Part 1: How do I wire a 3 pin thermal fan switch to the 4-wire harness?
Part 2: I explain how to do this
Part 3: Something about the viscous clutch fan?
Part 4: Now we're talking about the coolant temp sensor. ?? I don't know why either.
Part 5: Hold music? And then something about chinese parts.
Part 6: Now something is smoking and there is talk of cleaning the MAF and resetting the throttle b
I am completely lost after step 2.

part 3 was what initially had the mismatched wires.. Fan Control Sensor

that was made clear and I thank you .. fixed.

the reason I started digging into this was : dash temp gauge was not working.

which meant that the Engine Temp control sensor was bad.

I replaced it with a Oreilieys part. I did not get an o ring with it.

driving it home it stumbled on acceleration. ran but not very good

the steam and smoke was the Oreilieys sensor (old Oring) was leaking onto header.

I replaced it with an oem sensor. Fixed!.. temp gauge works.!


MY problem now is that the car stumbles and isn't running right.

sorry about confusion.. should i have started a new thread.?

[okar]

I have searched "stumbling" and "hesitation"


My confusion is that why, after changing the ECTS does the car not run right? misfires?

Cleaning the MAF was in reaction to the stumbling and hesitation...

NO the head gasket did not go, (relief) it never overheated.

[walky_talky20]

Ok. I mostly gotcha.

The ECTS is actually 2 sensors-in-1. Kind of like a Shampoo/Conditioner, if you will. (OK, not really). There is one "leg" of the sensor that is the dashboard gauge, and the other is for the ECU. It is entirely possible that the new sensor you have is actually junk. It may give a good dashboard reading, but the values going to the ECU could be completely wrong.

Other possibility is that in your recent dealings with the connector, the wires have become damaged and thus the ECU gets bad values.

Finally, the stumbling may not have anything to do with the recently changed sensor. You may just have a coil pack that decided to give up the same day you changed the sensor. It happens.

[okar]

http://www.audiworld.com/tech/eng47.shtml

hope this helps anyone looking to replace Engine Coolant temp Sensor

[okar]

Thanks again Walky !