[Solved] Car fan controller intermittent - Page 1
Forum section: electronics / repair

author: spilihps
author_rank: Regular Contributor
timestamp: January 20, 2017, 01:33:53 pm
content: Hello everyone!I have a Volvo 850 with an ECC unit, that have been giving me some trouble lately.It sometimes shuts down the fan completely, and it is very random, but tends to be more often at the "first start of the day".It first starts as usual and when it gradually rises the RPM when the Engine coolant-temp rises, and then it just shuts down completely.To get it going again, i just have to restart the car, and in 9 cases out of 10 after that restart it works rest of the day.And i also seem to notice that it is more often when its Cold outside.The ECC consists of a main controller unit that have the user Controls and sensors and such, and then there is a controller unit just for the PWM of the fan motor. It recieves a controller signal from the main ECC Control unit.Ive tried changing the main ECC unit with a known working one, and the problem is still there. So next thing was to pull the fan controller apart. And for a moment i was hoping it to be the main transistor, however after searching the web, i noticed that it seem to be extremely rare with an intermittent transistor.The fan controller board doesnt have much "intelligent" ICs on it, just two op-amps, the rest are just discretes. And also somekind of varistor that is connected over the transistor.Also the ECC unit does have quite a large list with internal diagnostics, but it have not set any fault codes, this leads me to Think that it is "Close" to the Power-transistor of the fan.. I may be completely wrong though..So, any ideas on what too look for or test? I attach a couple of images of it.Any help is appreciated!

author: max_torque
author_rank: Super Contributor
timestamp: January 20, 2017, 05:12:31 pm
content: I think you'll need to break out the scope and monitor the control signal to the fan motor controller. That way you can find out if it's a fault with the control signal, or the wiring loom carrying that signal, or a fault with the fan controller itself. Once you have understood what the control signal is (often a 100Hz square wave PWM signal btw) you can also drive the fan controller directly on the bench and see if it reliably responds etc

author: spilihps
author_rank: Regular Contributor
timestamp: January 20, 2017, 06:15:45 pm
content: Hello!Thank you for your answer.The wiring-loom between the ECC control unit, and the fan control unit is very short, and that is inspected.Also, as stated the ECC control unit is swapped with a known working one so the fault is somewere else.And, the ECC unit does have a fault code for "fan control signal missing" (that i think is somekind of loop-back maybe?) and that is not triggered.and final, ive seen several reports that the fault disapears once the fan controller is changed for a new one.The bench-drive is a very good suggestion, however, i think this will be very hard to catch the fault in the act, since its very seldom that this happen..

author: helius
author_rank: Super Contributor
timestamp: January 20, 2017, 06:25:17 pm
content: Volvo P2 fan controllers come in two types, automatic and manual. The manual type has a huge resistor that is used with the speed control pot to control power to the fan. The automatic type uses a chopper circuit with a power MOSFET 2SK1423 to switch power to the fan with PWM. This device seems to be somewhat under-rated and often burns out.I fixed it with a FDA032N08 which has higher maximum VDS, and applied new Shin-Etsu thermal compound. The MOSFET gets very hot when operating and relies on cooling fins inside the fan airstream. If the air duct gets blocked (by a loose fresh-air door for example) it starts cooking immediately.The diagnosis for failed MOSFET is a short from gate to source using the diode test mode of your multimeter. If it isn't shorted, I believe the transistor is still OK (but thermal paste may be dried up and useless). You can check the control signals between the ECC and fan controller in-circuit to get a better picture of what's happening. Presumably you've tested the fan itself.

author: spilihps
author_rank: Regular Contributor
timestamp: January 20, 2017, 06:30:18 pm
content: Hello!Thank you for your reply!Yes, this is the ECC one with the MOSFET you refer to.And was my main suspect until i read that intermittent FET's are extremely rare?How did yours fail?

author: james_s
author_rank: Super Contributor
timestamp: January 23, 2017, 04:48:51 am
content: Are you sure the fan motor is ok? It's possible that it's drawing excessive current and the controller is shutting down. The fact that it acts up more when it's cold supports this as a possible cause, the grease in a cold fan motor will be thicker and it will draw more until it starts spinning.I also have a Volvo but it's old enough that the fan controller is just a couple of power resistors in the air duct. When the original fan motor failed it melted the fuse.

author: spilihps
author_rank: Regular Contributor
timestamp: January 24, 2017, 09:18:56 am
content: Hello, and thank you for your input.Well, the fan spins freely, and it doesnt make any noise, i know they get squeeky when they get tired, but this is quiet.I the same thought a while back, so instead of auto fanspeed i set the speed to several different speeds to test it out, but it seems to be the same problem even at low speeds..Also, it apperantly have a faultcode for that also, called "siezed fan motor" and that is not triggered either.

author: Robomeds
author_rank: Frequent Contributor
timestamp: January 25, 2017, 03:09:23 am
content: I had a SAAB of about the same time period as the 850. My SAAB had the electronic fan control and a similar circuit to control it. The large power transistor died on mine. Once I replaced it all was well. Note my just stopped working. I didn't have the variable issue you are facing.Not much help but I would start with the power transistor.

author: Armadillo
author_rank: Super Contributor
timestamp: January 25, 2017, 03:42:56 am
content: I am thinking that the fan should be a DC motor with carbon brushes. Maybe you should check the carbon brushes or had it changed anyway if the time is too long. I think you should check the motor separately from the electronics by powering it from the battery directly with wires and discover any intermittent behaviour before going to the mechanic. Run the fan for awhile, say 10 minutes.

author: spilihps
author_rank: Regular Contributor
timestamp: January 27, 2017, 01:35:56 pm
content: Hello again!thanks for all your input.I replaced the FET as a gamble, and its been three Days with no problems at all. However, i will need to test it atleast a week more too be 100% sure that it is OK.Will keep you posted.Thank you

author: 45Overload
author_rank: Contributor
timestamp: January 28, 2017, 05:50:11 pm
content: If the fan control system works OK after a restart, then the problem is not in the PWM fan control module. Is the fan motor itself a d.c. motor with commutator? So many possible problem areas including monster firewall connectors. What about the temp sensor signal? I wouldn't waste any more time on troubleshooting if I were you. just put in a DC_Control fan controller. Mine has been running great for over 10 years. PWM control of high-amp d.c. motors is tricky and the controller should ideally be mounted as close to the fan motor as possible. I can't prove it, but an aging d.c. fan motor could easily be the reason the controller fails.

author: spilihps
author_rank: Regular Contributor
timestamp: January 28, 2017, 06:24:30 pm
content: Quote from: 45Overload on January 28, 2017, 05:50:11 pmThanks for your input.Please elaborate what makes it impossible to be the fan control circuits?We can be sure of that it is no problem with any temp.sensors, for one major reason, it should never shut down the fan completely based on temperature, it Always ventilates the cabin.I will keep the original system design.

author: 45Overload
author_rank: Contributor
timestamp: January 28, 2017, 07:34:09 pm
content: It appears you are talking about the cabin fan and not the radiator fan. Sorry my mistake. Looking at your first post I would say this is a perfect description of a failing fan motor. In other words, the shaft/bearing is getting sticky or for whatever reason spins up too slowly and draws more current than it is supposed to. I'll bet someone on the volvo forums will know about this problem..You mention that after it operates for a while, everything is OK, which would also support the faulty fan theory above. You can put in a bigger FET, but that's really a band-aid. The motor is drawing too much current at cold start.

author: spilihps
author_rank: Regular Contributor
timestamp: January 28, 2017, 07:59:38 pm
content: Hello. Oh okey, that explains it!I Think that a sticky fan motor, would trigger the "siezed fan motor" error code, however there is none.Also, this fault have been in the car for about two years, and it have not been getting neither worse or better.Actually ive only found one more that _exactly_ explains this at the volvo forums, and they replaced the whole PWM controller, and the fault was gone.I have replaced the FET, and the problem have not shown up since then. So far so good. But like i said, in week or so, we will see if the problem really is gone.

author: 45Overload
author_rank: Contributor
timestamp: January 29, 2017, 01:46:35 pm
content: These automotive things don't follow logic too well. Sure, the designer might not have done his job and the controller wasn't beefy enough to last a long time. My Jeep has a similar PWM radiator fan control that fails shorted, but the fan motor is OK. Or, small motors can and do get sticky bearings and require more current to get them up and started. A new module "fixes" the problem because the old one had burned parts. The interesting question is whether the new module is identical the old one, and will fail again after the same time period. Small d.c. motor difficulties are one reason you are seeing more and more BSL electronic motors for radiator fans and so forth. Easy to control but expensive to replace.

author: spilihps
author_rank: Regular Contributor
timestamp: February 09, 2017, 08:57:41 am
content: Just an update.I can now confirm that replacing the FET did the job!The unit have worked flawlessly since i replaced the FET.Very interesting to have an intermittent transistor though..Thanks to all for your help!

author: james_s
author_rank: Super Contributor
timestamp: February 09, 2017, 04:12:00 pm
content: Always good to hear a followup, especially on a successful repair.I've never seen that particular failure before, although I did once have a small signal FET in an audio amplifier develop an intermittent fault where it started producing static in the audio occasionally. In your case I suspect one of the bonding wire welds may have been flaky.