Auxiliary Fan Switch

[alexverve]

Does anyone know what sensor controls the secondary electric fan? i am trying to resolve issue with my engine slightly overheating @idle. As i mentioned, fan module was switched - no changes. Now i am going over the sensors that measure temperature. there is a blue 4-pin sensor called Auxilary fan switch, i believe it comes only in one setting. There is also a Auxilary pump switch - 2-pin that controls the way secondary pump and auxilary fan run after engine is off. that one comes with "lower temperature" option. In any case, my questions are:
1. does 2-pin pump fan in any way affects the way fan runs at idle? i want to have my second fan come on earlier. if it does with engine off -does it do same with engine on?

2. are there any 4-pin sensors that have "lower temperature" option as well?


Thanks in advance.

[The_Jerbel]

1. No. It's only with the engine off.
2. You should just replace the sensor with a new one. They get old and less effective over time. It's the sensor on the lower rad hose.

[MacDaddy]

I think the one your referring to is the sensor in the A/C condenser, its on the passenger side, i believe under the headlight and behind the bumper (removing the headlight should provide access IIRC) just remember to mark the headlights original position or you may end up resinstalling it and having your lights mis aligned.

[The_Jerbel]

No, that's an A/C switch. He's talking about a rad fan coolant temp sensor, which is on the lower rad hose, like I mentioned above.

[MacDaddy]

he mentioned four pins, which the sensor on the condenser has, the sensor in the lower rad hose only has two. If you read the information PDF that was for dealers it mentions that sensor and the role it plays in controlling the auxiliary fan.

[mholme]

[alexverve]

^^^thanks.

[MacDaddy]

^^^thanks.

X2

[The_Jerbel]

Ok, I'm not sure if the OP is referring to the after-run switch on the back driver's side of the motor, as well as the aux. fan switch on the lower rad hose, or what he's talking about. The A/C switch on the condenser definitely affects the fans, but I don't think that's what he's talking about.

[MacDaddy]

The A/C switch on the condenser definitely affects the fans, but I don't think that's what he's talking about.

why is that?

there is a blue 4-pin sensor called Auxilary fan switch, i believe it comes only in one setting.

2. are there any 4-pin sensors that have "lower temperature" option as well?

correct me if i'm wrong, but the only sensor i know of that has 4 pins and has anything to do with the fans is the one in the condenser.

[alexverve]

correct me if i'm wrong, but the only sensor i know of that has 4 pins and has anything to do with the fans is the one in the condenser.

4-pin for auxilary fan that controls the fan with engine on.
http://www.ecstuning.com/Audi-B5_S4-...ooling/ES1873/

2-pin auxilary pump switch, the low temperature one - the one that keeps auxilary water pump and second fan on after u turn engine off..
http://www.ecstuning.com/Audi-B5_S4-...ooling/ES3326/

[The_Jerbel]

The first one is the sensor on the lower rad hose.

The second is on the back dr. side of the motor.

[alexverve]

if i want to check whether the first sensor sends signal to the fan at a time it starts overheating, anyone know using VAG what and where i have to check?

[mholme]

You can log the cooling system fan function in blocks 130-140ish I believe. Just dial it up to there and you should be able to check duty cycle of the stages with and without A/C fan activation.

[AudiSportB5S4]

You can log the cooling system fan function in blocks 130-140ish I believe. Just dial it up to there and you should be able to check duty cycle of the stages with and without A/C fan activation.

You are just a book of knowledge.

Let me ask you this, my aux. fan switch in the lower rad. hose is black... The new one is blue correct? Was there a revision? I think mine is busted. I'm having similar issues to Alex now! Once I come to a stop or even through town traffic I'm noticing the temp creeping up a little... I have an EFK and I don't hear it engaging as often it has become sporadic, sometimes it does sometimes it doesn't. And when it does engage its not staying on until the temp comes back down.

Alex- I think ever since you mentioned this to me, my car decided to do the same thing!! THANKS!

[alexverve]

You can log the cooling system fan function in blocks 130-140ish I believe. Just dial it up to there and you should be able to check duty cycle of the stages with and without A/C fan activation.

can u adjust temps with VAG at wich secondary fan comes on?

[alexverve]

You are just a book of knowledge.

Let me ask you this, my aux. fan switch in the lower rad. hose is black... The new one is blue correct? Was there a revision? I think mine is busted. I'm having similar issues to Alex now! Once I come to a stop or even through town traffic I'm noticing the temp creeping up a little... I have an EFK and I don't hear it engaging as often it has become sporadic, sometimes it does sometimes it doesn't. And when it does engage its not staying on until the temp comes back down.

Alex- I think ever since you mentioned this to me, my car decided to do the same thing!! THANKS!

one of the "explanations" of this, can be the fact that we have Oil Cooler in front, blocking part of radiator, reducing air flow. on the other hand, people with FMIC should be screaming "OMG" cause they r blocking way more. but i have not heard them.
is there in the VAST tune that affects those thermo switches? any "secondary" effect?
it is just weird. it only goes up to 103 degrees and then comes back - without fan Aux coming on... it is like WTF???

[AudiSportB5S4]

^ No alex, there is no bearing on the oil cooler, or the tune. Every time you say that, people who read are probably on the floor laughing. No, but seriously the switch in my case is probably busted. I've been running my hardware for quite a long time now and it's probably just shit the bed. Can't forget the parts don't only have X miles on them, they have 8-10 YEARS. This is the only switch that is still factory on my car along with a few others, but in the cooling aspect, it is.

So I'm going to replace the aux fan switch and see if that does it. I have the EFK that nearly blows my engine out of the bay so I think it's just the sensor not telling them to run until its too late.

[mholme]

can u adjust temps with VAG at wich secondary fan comes on?

There's no adjustment through vag-com. The fans activate and deactivate at specified temps. All bets are off with you all that are running FMIC set ups and such that are having issues here. As far as a revision to the part, I'm sure it has been over the years, there have been tons of variations of this part over different platforms, not too sure whether it's specific to the B5. I'd have to look into that, been too long of a weekend for that right now.. If it is an issue, I would second what the jerbel said about just replacing the sensor as their functionality does diminish with age.

[alexverve]

There's no adjustment through vag-com. The fans activate and deactivate at specified temps. All bets are off with you all that are running FMIC set ups and such that are having issues here. As far as a revision to the part, I'm sure it has been over the years, there have been tons of variations of this part over different platforms, not too sure whether it's specific to the B5. I'd have to look into that, been too long of a weekend for that right now.. If it is an issue, I would second what the jerbel said about just replacing the sensor as their functionality does diminish with age.

mine was replaced recently... not sure if with a new or swap (as a trial) from another S4 - did not fix the problem.

[The_Jerbel]

There's no adjustment through vag-com. The fans activate and deactivate at specified temps. All bets are off with you all that are running FMIC set ups and such that are having issues here. As far as a revision to the part, I'm sure it has been over the years, there have been tons of variations of this part over different platforms, not too sure whether it's specific to the B5. I'd have to look into that, been too long of a weekend for that right now.. If it is an issue, I would second what the jerbel said about just replacing the sensor as their functionality does diminish with age.

^ Yup. Can't adjust aux. fan activation or deactivation temps with VAG. The current version of the switch is blue. Replace it, Mike, your problems will likely be solved.

[AudiSportB5S4]

^ Yup. Can't adjust aux. fan activation or deactivation temps with VAG. The current version of the switch is blue. Replace it, Mike, your problems will likely be solved.

Thanks Jordan... How've you been?! I haven't talked to you in quite a while.. Hope you are doing well

[The_Jerbel]

mine was replaced recently... not sure if with a new or swap (as a trial) from another S4 - did not fix the problem.

Check the wiring. That wire tends to get hot and brittle.

[The_Jerbel]

Thanks Jordan... How've you been?! I haven't talked to you in quite a while.. Hope you are doing well

Doing good, man. Just busy as a bee lately trying to get business taken care of and websites built. How have you been?

[bps4]

^ Yup. Can't adjust aux. fan activation or deactivation temps with VAG. The current version of the switch is blue. Replace it, Mike, your problems will likely be solved.

To replace this switch, do you have to drain the coolant? How does the switch attach to the hose?

[bps4]

In case anyone finds this useful now or in the future, I found out we can't the status of the fan relay switch to see if it kicks on when the coolant temp reaches different thresholds. Certain other Audi models can. See 078-907-551-AZA.lbl in your VAG-COM labels directory for more details.

[Samap]

I am going to replace the auxiliary fan switch because it doesn't turn on at all. The fan still works connecting 12V to the fan, and jumping the sensor switch in the lower radiator hose activates it, so it is the fan switch. But I noticed that the clip holding it in to the lower radiator hose is right up against the radiator and if I want to take it out, I might have to flex it and angle it out, or break it and replace it. But then can it be clipped back in from the opposite side just so it's easier. Also, I'm thinking that coolant will come out when removing the sensor, anybody know how much will come out, how fast, and if putting the new sensor switch in real fast will be okay.

[bps4]

Just drain the coolant - theres a good chance your face will get covered in coolant if you don't