996 fans not working

Hi i have a 2000 996 and I noticed today that my car had reached 101c (213f) and my fan had not kicked in at the front but the rear engine one had, however when I turn on the air con they work fine, has anyone else had this? Or know what could be at fault? Any help would be greatful Thanks Dan

Does your air conditioning come on the last setting as you switch on the engine? Mine does and I think that is the normal so in actual fact your fans should kick in anyway. It might be better to have the air conditioning on manual (very low) and then you know that the fans will kick in, when needed, to cool the rads. My temp gauge needle hangs about vertical or on the 0 of the 180F mark. No more.

Yes the air con come on when the engine is switched on and the fans kick in so I know they are working fine they just don't seam to kick in when it reaches the temp they are meant to, 102c as it showed via the display hack on the heater display is when the high speed should come on and still nothing other then the engine compartment fan. Does anyone know if there's a fan switch or if it could be a faulty coolant temp sensor?

Hmm on mine the hi speed fans seem "locked in" to the engine fan. I've never seen one run without the other. That said, I remember some language about coolant temp. and/or pressure, so I'll need to look for you. I think they use the same sensor, but I'll double check. The "switch" is the DME, if I'm not mistaken. I doubt the DME is bad. Minor note, I'm not the only one whose hi speed fans come on at 107-8c (not 102). The only other ways I know to test high speed are either Durametric, or jumper from low speed relay, or 12v power source directly into relay (but be prepared for 30amp draw). Get familiar with that click sound when you turn on your low speed, and feel with your fingers. The high speed relays do that same click when they turn on.

The essential companion writeup is excellent, but it's 2 pages long, so here's a link to that: http://books.google.com/books?id=Raa...essure&f=false That link is those 2 pages, the free sample whatever, at least on my browser.

With the car cold, when you turn on the AC, both fans will run at low speed. Once the car heats up, both fans will run at high speed. If one or both fans don't run on low, then its most likely the ballast resistor. First, swap the relays around (there are 4) to rule out a bad relay and of course check the fuses. If the fan(s) doesn't run on low, but does on high, then its pretty likely its just the ballast. If a fan(s) doesn't work on low or high, then its probably the fan. If its a bad ballast, I would buy both the fan and ballast. The ballast at Partgeek is around $120 and the ballast fan combo is around $170. Once the ballasts start to go, the fans are not far behind, so its easier just to replace both and not have to do the same job over again in a few months.

Thanks for all the replies I have replaced the ballast resistors, cleaned out the rads, fitted a LTT and full coolant flush and refill about 6 months ago. All I can think is it's the water pump causing it to get hot but I'm not sure why the fans are not kicking in

The temp sensor of 996 MkI actually has two independent sensors inside. One connected to the instrument cluster directly (presumably driving the coolant temp gauge) and the other one connected to the DME directly. I don't know which sensor input the climate control uses to report the coolant temp and I wonder if the behavior you observed (cooling fan not turned on at the set temp) could be because of any discrepancy between the two sensors.

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Good thinking. This is then a good place to put this. To the OP: All of my observations regarding at what temperature the fans come on low speed or high speed, and at what temperature the fans shut off, have been made with an OBD2 test tool connected to the OBD2 port and displaying coolant temperature in real time. If in your car's case you are sure the fans aren't coming on when they should yet come on with the A/C this is as others have correctly stated a problem with the fan resisters. I've had one of these fail on my Boxster. The engine coolant temperature ran a bit higher than normal, even allowing for the fact the coolant temperature gage is not that precise an instrument. Same is true with my 996 Turbo, which has had both fans quit at two different times. No real overheating just the coolant temp gage needle running a bit further to the right than I was used to seeing. But at not time did the coolant temperature gage even get close to the scary upper temperature reading range. In your car's case if *both* fans do not come on when they should at the 1st temperature threshold (212F by my observation (but this temperature may be different for your car) the engine will run hotter than normal. The next threshold for when the fans switch to high speed is (for my car at least) is 216F. (Fans shut off at 205F.) As I have mentioned before I have driven in extremely hot ambient temperatures of up to 116F (in the Boxster, even hotter in the Turbo) and even with the Boxster fans on high the coolant temperature stayed at 226F. (The Turbo runs much cooler due to far better cooling, due on part to better aerodynamics, but also due to more aggressive fan operation.) Bottom line is you need to be sure the fans are working correctly.

OP, when your car is cold and you turn ON the a/c, do your coolant fans come on? If they do, that means their low speed is fine so the resistors are fine.

Yes when I turn the a/c on when the engine is cold the low speed fans come on like they should, but when it was showing 101c on the heater panel there was no fans on at all, and when traveling at 80mph the temp still raises to that speed until I have to put the high speed fans on manually which then it drops back down to about 78c-82c

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Ok, that's the way I understood your original post as well. So basically it appears that the DME is not commanding the fans to turn on at the proper temp thresholds. Only the DME controls and commands the coolant fans (the climate control unit talks to the DME directly). Since your fans turn on when a/c is engaged, your DME-fan circuits are fine. I checked. The coolant temp the climate control displays is from the DME so no, I can't explain why the DME sees high temp yet it does not command the fans to be turned on.

I just don't have a clue either, looks like a trip to my local porsche indie to let them look at it

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That's a bug in the climate control hack. Turn off that hack and I bet it works. If not, let it get up to 108c and I bet it kicks on.

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Hello, isn't this what I just posted above?

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What do you mean you have to put the high speed fans on manually. There is no way to put the high speed fans on manually unless you have hacked the cooling system electronics. I have no idea what you are saying. Please describe exactly what you are doing.

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I have a switch tapped into the hi speed fan relays so I can put them on at any time ie for track day, or on occasions like this

Removed the water pump last night and it all seamed to be in good order but fitted a new one anyway seen as I was there, and got a new coolant temp sensor but is there a was of testing the old one to the new one ie plug it in and put it in a kettle abd see if it brings the fans on?

Right so quick update, fitted a new explanation tank, coolant cap, level sensor, water temp sensor, water pump and refilled and bleed the system correctly and it's still running into the 100c mark with no fans kicking in! anyone have any other ideas? Looks like it might have to be a garage job

Have you tried Phil's suggestion of disabling the OBC hack a few post above?

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Yes I have disconnected the battery and reset the system, I removed the fan hack and didn't use the obc hack, I don't see what else could make the temp rise so high under normal driving

If it's really true that your engine purge fan was "on" at 101c, and it's hard to see those blades unless you open the lid, then: 1. The engine fan might be coming on a bit early (according to that book). 2. I'd like to know exactly what temp that engine fan is coming on. 3. I'd be tempted to jumper the low speed relays to the engine fan relay, to isolate this as a DME bug. 4. All the information you've given us is pointing to a DME bug, which I've never seen mentioned in all my browsing. 5. If my DME had a bug, I'd consider that an opportunity to ask for free DME diagnostics, software update, stuff like that.

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The engine fan was on at 98c ish but I'm not sure when it kicks in, how would I link the radiator fans into the engine fan?

The engine fan relay is relay 8 on the DME/Relay panel behind the carpet - behind the rear seats, according to a simple search I just did, you might want to verify it. The concept would be to jumper that to a low speed relay under the dash. The schematics for those, along with some good detail re: sensors, DME, relays, is here: http://www.renntech.org/forums/topic...ting/?p=179562 I like that schematic. It shows that the DME communicates directly with the fan1 relay, and then the fan2 relay feeds off that.

Thank you it might help to do that while I try to find out the reason/reasons for the fans not coming on correctly

Also from that thread - "This is where a PST2 or PIWIS tester is very handy. With one of those testers you can test each circuit individually to narrow the problem down. You can also view the temperature the sensor is seeing. So rather than trial and error you reduce the number possibilities and narrow the problem down." The old money issue.

Upon further reflection, my idea to jumper a low speed fan to the engine fan is really just to prove (to a dealer or indy): "I've proven the low speed fan is capable of responding to a temperature driven signal from the DME, albeit the engine fan signal, so what's wrong with the DME that it's not signaling the low speed fan?" Perhaps an easier idea would be to build (or buy) a relay socket diagnostic light, plug it into a low speed socket, and watch it not light up as temperature rises well past the trigger point. That enables you to say (to dealer or indy) "see, the DME is not signaling the fan like it should." Overkill on this idea would be to also add a light to the engine fan relay so you could say "See, the DME signals the engine fan but not the rad fan." The brute force method (which I always like) is to get a debug trace (diagnostic report) from the DME in regards to when it thinks it's signaling the rad fan. I'll need to search to see if that exists and cost, but it might be a long search.

Wow that some great information thank you, it's a good place to start and trace it back. I'll have a look into making something to light up when the fan is meant to switched on and go from there then. Cheers again

Maybe I'm missing the intricate logic here, guys but Tookey said "Yes when I turn the a/c on when the engine is cold the low speed fans come on like they should, but when it was showing 101c on the heater panel there was no fans on at all". Since the coolant fans are controlled ONLY by the DME (via the fan relays) and the fans do turn on when a/c is engaged, doesn't that already prove the DME has no problem activating the fans, the fans are working so fans not running can only mean DME NOT enabling the fans? Of course the mystery here is WHY the DME is not enabling the fan despite high coolant temp.

I think one thing not clear to me is whether the connection between the DME and the high speed fan relays are intact. Any chance something is disconnected when you hacked into that high speed circuit? Even if the DME was disconnected from the high speed fan relays, I still can't explain why DME does not enable the fans at low speed. Again, the a/c was the proof that the DME can activate the fans at low speed. BTW, how did you tap into the high speed relays for your manual fan operation?

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The fan hack is basically a wire connected to the earth pins on the high speed relays with the other end going to one side of a switch then another wire from the second side of the switch to an earth on the chassis, so when the switch is pressed the relay is earthed and activates the fans. So to clarify yes the low speed fans come on with the a/c but not when the coolant hits the activation temp, how ever the engine purge fan has kicked in fine

Wow, my life's been so crazy it's been forever since I've posted anything. Tookey, did you solve you problem? You said your fans aren't kicking in at 101C, but for what it's worth I ran some tests on my '01 this evening and my low speed fans don't kick in until 103C as shown on the climate control hack. I assume it's the low speed because there's nothing before 103, and it's the same sound as when I turn on the AC which I was told also turns on the low speed (not the high speed). Not sure I've ever heard the high speed. Also, my rear engine fan I don't ever remember coming on (I need to look into that) so I can't comment on the simultaneity of that fan with the fronts.

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The engine compartment fan is also controlled by the DME based on the engine compartment temp sensor, which sits between the plastic intake runners on bank 2. Usually the engine compartment fan turns on only when the car is stationery (e.g., you park your car in the garage after a drive in a hot day). When the car is moving, the engine compartment temp won't get that high to trigger the fan, unless the temp sensor fell down and sat on top of the engine (some ppl had this happened to them so their comp fan turns on quite frequently).

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The ground pins? To which pin (numerical, please) are you referring?

Rather than starting a new thread thought I'd piggy back off of this one with my question/confusion. I have both a 2004 C2 and a 2004 C4S. I just recently noticed that the cooling fans on the C2 only come on at temp, run for a few seconds then shut off. I asked the tech about this as I seemed to recall that with the A/C on at start the fans ran at low speed. Had the WP replaced and cooling system flushed and it was after that that I noticed the fans don't come on as I thought they once did. Tech's reply was the car was not running hot and the fans come on at the proper temp so I don't have an issue. But now that I am paying attention I notice that the fans on the C4S do run at what seems to be high speed with the A/C on at start. Does anyone know how the fans are supposed to behave? If they come on at start when cold with the A/C on do they shut off at some point or do they run constantly? Any suggestions as to what I can do to better observe their operation? Thanks in advance.

On my '03 C2 the fans are ON at low speed whenever a/c is ON. In addition, if the engine temp is really high, the fans are ON high regardless of a/c. When a/c is OFF, the fans will only come on Low at temp, around 200F from memory, then they will come on high at even higher temp.

in my case the fans never came on, this was to blame, although the cluster showed engine temp perfectly

I hate to dig up an old thread, but my 99 Cab fans will not come on at any temperature up to and including 108C (indicated by the AC Hack, and verified - kind of - by the water temp gauge well past the 0 and nearly touching the 2nd mark). Here's the strange thing - I can turn on the low speed fans by just turning on the AC up to and including 100C. The high speed fans with come engage at 102-104C, again, when the AC is on. But when the AC is not on, no fans will come on at all (neither low nor high). This seems bizarre to me...

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Hey mine does the same, Manuel mode of the ac comes on when I turn my key. The compressor is not on tho. I always cut mine off before starting. Should theses be left alone for the front fans to be activated when needed. What I'm asking is, if you turn off everything will our fans still run upfront when needed if the ac is cut off?

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It is bizarre if the coolant temperature is indeed 108C (226F) and the fans are not running at all. If this is truly the case I have to wonder what keeps the coolant temperature from continuing on higher? (Have you checked for a blown fuse in one of the radiator fan fuse locations?) My experience is 226F is the maximum coolant temperature I've ever observed using an OBD2 code reader/data viewer connected to my 2002 Boxster's OBD2 port. One time the ambient temperature was 116F. (Location: southern AZ in July.) The intake air temperature was 135F. Even driving down the freeway at 75mph the coolant temperature stayed at 226F. The fans -- I checked before I got on the freeway -- were running at high speed. The coolant temperature only dropped lower once I drove out of the extreme heat. The next time the ambient temperature was in the mid-90's but I was hammering the car on a nice mountain road. In this latter case I tried to get the temperature to go higher but it never went above 226F. The radiator fans were running at high speed just like in AZ. While I have not observed this directly with a 996 -- I have observed this with my 2002 Boxster and using an OBD2 code reader/data viewer to view the coolant temperature in "real time" -- I believe the radiator fans should come on low speed when the coolant temperature reaches 212F. (I believe my 996 Turbo behaves similarly but I can't recall explicitly checking this. I know the Turbo runs lots cooler under the same ambient and driving conditions.) Furthermore, if the coolant temperature continues to climb to 216F the fans are switched to high speed. In either case the fans run until the coolant temperature drops to 205F (96C). Also, both fans come on at least low speed when the A/C is turned on, the snowflake is lit, to the best of my experience regardless of the ambient temperature (unless the ambient temperature is low enough (near 32F) the A/C compressor is not engaged to prevent possible freezing of the evaporator). Over the years I have had just a couple of radiator fan problems with my Porsche Boxster and Turbo. One with the Boxster was the passenger fan would not come on on its own. This proved to be a bad ballast resister (which is how the fan is operated at low speed). The tech told me these resistors are located in a kind of out of the way location but road splash can take its toll on them. Or what the tech said he sees often is someone has been "in there" and not put the radiator wiring and ballast resistor where it really belongs but just jams wiring/ballast resistor in between some plastic panels. This can result in a shortened ballast resistor life if this new location doesn't shield the resistor from road splash or causes it to run hotter. I do not know if a problem with one side could affect the other side. It didn't in the case of my Boxster though there might be a ballast resistor failure that could affect both sides. Or a problem that blows a fuse. In another case, this with my Turbo, the passenger side radiator fan motor was running but no air was being blown out the radiator exhaust. This proved to be due to the radiator fan motor shaft which had snapped. Fortunately, while the radiator fan contacted the back of the radiator and bent some fins, the radiator was not holed. (CPO warranty though had both the radiator fan motor, fan, and radiator replaced.) The tech told me what I suspected: This is a very rare event. In fact mine was the first one he had ever encountered. At another time the Turbo driver side fan was running but it wasn't moving nearly as much air as the passenger side. There were no blockages. The tech checked and there were no fan stage errors but the current draw was high. I had him replace the fan motor. After replacement the new motor had the driver side radiator fan blowing a gale, just like the passenger side radiator fan. In your car's case a Porsche tech can connect a Porsche diagnostic computer and I believe at least check for fan stage errors, possibly even command the fans to come on low or high speed regardless of the coolant temperature. This "testing" will probably lead to a cause of the behavior.

I didn't check the fuse yet on the basis that if the fans come on with the AC then the fuses cannot be blown. Now that I think about it, though, suppose the resistor ballast are only there for the fans when the AC is not on. Perhaps that could be the clue. I'll have to take a look tomorrow. I am able to turn on all fans and validate that they work with Durametric.

With AC on the fans are both on at low speed. With AC off the fans switch on at low speed when reaching 104C and switch off again when temperature has dropped to 100C. If the temperature would continue to rise at 107C the fans go to high speed. This is on a Mk.1 C2 without a 3rd radiator, temperature read out from the AC display.

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I wanted to come back and let everyone know that my fans are indeed coming on and off at the correct temp. Why then did I post the above? Because the temp reading at the HVAC hack and gauges is WAY off compared to the values you could see when polling the DME through ODBII or Durametric. I suspect this is true for �99s more than others. So for those of you thinking your fans are not coming on or you think your engine coolant temps are high, please check via OBDII or Durametric, not the dash gauge or the HVAC hack. I though I was hitting really high numbers (115C) but in fact was only hitting 101-102C before the high speed fans would come on. It turns out, the fans come on and off at exactly the right temps when measured via ODBII/Durametric.

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^^ Good to know... I could see someone getting obsessed with this and chasing their tail for a long period of time!

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I know this was an old bump, but wanted to search before I made a new thread. I noticed my dash temp gauge seems to be reading higher than I *think* it should at low speeds (although tbh not positive) but never thought of plugging in OBD2 and comparing. Will give it a try.

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Do it!

hello guys I have the same problem I'm going crazy :/ the 2 fans on the radiators worked but a stone pierced the right radiator. I replaced the right radiator and now when the fluid temperature reaches 102 � up to 110 � the fans do not start automatically the fuses are ok the fans run at low and high speed if I activate the air conditioning I checked the temperature of the probe using a Chinese OBD and durametric tool, the probe temperature is ok Using Chinese durametric, I checked if I had any errors on the DME, RAS nothing the left fan should work as the radiator has not been touched remove. I have checked the connection of the electric socket of the right radiator c is ok I understood that it is the dme which sends the order of ignition of the fans according to the temperature but I don't think the DME is bugged after replacing the fans the rear fan radiator for engine is working properly I've been looking for no way out for 3 days however this problem has happened to several (seen on the internet without a solution) thank you

Those 102 � up to 110 � degrees are being reported to the DME - and not the dash gauge/HVAC hack, correct?

" Those 102 � up to 110 � degrees are being reported to the DME - and not the dash gauge/HVAC hack, correct?" dear Mike, I control the temperature with the display dash gauge/HVAC hack and by the plug "Chinese" durametric. I am going to change the temperature sensor near the engine pulley....

On my car, the numbers displayed on the HVAC hack do not match what the DME actually shows. I�ve used a simple ODBII Bluetooth device and iPhone app, and that device shows my temps closer to 97C and 101C when the HVAC showed 107C and 116C. Are your numbers matching up? I�m not sure what a Chinese Durametric is, but a regular (official) Durametric did the same for me. In other words, I used a Durametric to validate my ODBII device was accurate, and it was, but the HVAC/Dash Gauge are not.