SLK/R170: SLK320 Radiator fan runs constantly at high speed
05-07-2014, 01:00 PM
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2001 SLK320
SLK320 Radiator fan runs constantly at high speed
Hi all,
Previous Work
I've owned a 2001 SLK320 for the past 2 years. I haven't had too many issues, other than replacing the Pneumatic Control Unit due to the classic flooding issue, and replacing the crankshaft position indicator. I did these repairs awhile ago and they went perfectly, so I don't think they're related.
The Issue
As of a couple of weeks ago, the main radiator fan (i.e. the big one that's right in front) has been running at full speed all the time when the car is on. On most days, about 10 seconds after I turn the car on, the fan will just kick into high speed and stay on no matter how long or how fast I drive. If it's a little bit cooler out (say 60-70F, which is cool for this time of year in Texas), the fan won't kick in until the engine warms up a bit, say to the 80-90F level. The fan is incredibly loud when it runs, such that it can be heard inside the car.
Diagnostics
The engine temperature seems to be normal; the car starts off cool, and within a few minutes will warm up to the normal operating temperature of ~180F. It's never gone higher than this. There are no check engine or warning lights. The coolant level is fine, and it has never leaked coolant. I've hooked up an OBD, and there are no warnings and nothing looks out of place. The temperatures read fine, O2 sensors look okay (I think), and the MAF seems to be responding the way I'd expect. Basically, nothing sticks out as been incorrect, although I don't have a great idea of what all the exact values of everything on the diagnostic should be.
Possible Repairs
I've searched and searched for info on this issue, and I've seen the complaint come up a lot, with few people saying how they actually resolved it. Most posters suggest it's one of four things:
1. I've bought a new temperature sensor and thermostat, but haven't installed them yet. Since the engine temperatures read fine both on the instrument cluster and OBD and it's not overheating, I assume these are fine, but the components are cheap and the repair is easy so I'll just do it this weekend just in case.
2. I've heard folks say a faulty Mass Airflow Sensor could cause this. Right now the OBD gives me an air flow rate from the MAF that seems to be reasonable, and it changes when I give the car some throttle, so I assume this is working okay. The ambient air temperature also seems to read fine. I sprayed things with a bit of contact cleaner just in case, but it didn't make a difference. Am I right in thinking that if I can see this stuff on the OBD, the MAF is probably fine?
3. It could be the fan itself. However, I see a lot of posts say people replaced the fan thinking it was it, and it wasn't.
4. Apparently, the fan on this car is not controlled by a relay, but instead, by the car's main computer AKA ECU / ECM. Folks have suggested that something can go bad in the ECU and for some reason the fan won't get a signal from it, causing the fan to go into a failsafe, panic mode of being always on full blast. This is the most expensive repair, requires reprogramming, and is difficult to diagnose, so I'm hoping it's not this. I'm also a bit wary of this fix, because the people I see recommending it conveniently always seem to be working for a company that sells and reprograms ECUs, and I've seen a couple people say they replaced their ECU and it didn't fix the issue.
I also am not too sure that the ECU failure makes sense; if the fan was never getting a signal, shouldn't it always be on? How could this issue be sensitive to temperature if the fan doesn't know what the temperature is? Is there somewhere else the fan can get temperature information from?
Questions
1. Has anyone here had this issue and resolved it?
2. Am I right in thinking that if the OBD looks okay, the MAF is okay?
3. Is there anything else I should be checking out in the OBD? For example, what should the O2 sensors be reading? What are some normal MAF values?
4. Is my logic about the ECU correct?
5. If the ECU is "bad," does anyone have any idea what about it goes bad? I have a lot of hands-on electronics experience, so if it's just some cap or relay that goes bad, I have no problem with taking that sucker out and fixing it.
6. I've also heard someone mention that this could be an issue with the fan clutch..? i.e. the fan only has one speed right now because the clutch has failed. How would I go about testing it?
7. Any other ideas about what might be wrong?
Thanks for your help!
Previous Work
I've owned a 2001 SLK320 for the past 2 years. I haven't had too many issues, other than replacing the Pneumatic Control Unit due to the classic flooding issue, and replacing the crankshaft position indicator. I did these repairs awhile ago and they went perfectly, so I don't think they're related.
The Issue
As of a couple of weeks ago, the main radiator fan (i.e. the big one that's right in front) has been running at full speed all the time when the car is on. On most days, about 10 seconds after I turn the car on, the fan will just kick into high speed and stay on no matter how long or how fast I drive. If it's a little bit cooler out (say 60-70F, which is cool for this time of year in Texas), the fan won't kick in until the engine warms up a bit, say to the 80-90F level. The fan is incredibly loud when it runs, such that it can be heard inside the car.
Diagnostics
The engine temperature seems to be normal; the car starts off cool, and within a few minutes will warm up to the normal operating temperature of ~180F. It's never gone higher than this. There are no check engine or warning lights. The coolant level is fine, and it has never leaked coolant. I've hooked up an OBD, and there are no warnings and nothing looks out of place. The temperatures read fine, O2 sensors look okay (I think), and the MAF seems to be responding the way I'd expect. Basically, nothing sticks out as been incorrect, although I don't have a great idea of what all the exact values of everything on the diagnostic should be.
Possible Repairs
I've searched and searched for info on this issue, and I've seen the complaint come up a lot, with few people saying how they actually resolved it. Most posters suggest it's one of four things:
1. I've bought a new temperature sensor and thermostat, but haven't installed them yet. Since the engine temperatures read fine both on the instrument cluster and OBD and it's not overheating, I assume these are fine, but the components are cheap and the repair is easy so I'll just do it this weekend just in case.
2. I've heard folks say a faulty Mass Airflow Sensor could cause this. Right now the OBD gives me an air flow rate from the MAF that seems to be reasonable, and it changes when I give the car some throttle, so I assume this is working okay. The ambient air temperature also seems to read fine. I sprayed things with a bit of contact cleaner just in case, but it didn't make a difference. Am I right in thinking that if I can see this stuff on the OBD, the MAF is probably fine?
3. It could be the fan itself. However, I see a lot of posts say people replaced the fan thinking it was it, and it wasn't.
4. Apparently, the fan on this car is not controlled by a relay, but instead, by the car's main computer AKA ECU / ECM. Folks have suggested that something can go bad in the ECU and for some reason the fan won't get a signal from it, causing the fan to go into a failsafe, panic mode of being always on full blast. This is the most expensive repair, requires reprogramming, and is difficult to diagnose, so I'm hoping it's not this. I'm also a bit wary of this fix, because the people I see recommending it conveniently always seem to be working for a company that sells and reprograms ECUs, and I've seen a couple people say they replaced their ECU and it didn't fix the issue.
I also am not too sure that the ECU failure makes sense; if the fan was never getting a signal, shouldn't it always be on? How could this issue be sensitive to temperature if the fan doesn't know what the temperature is? Is there somewhere else the fan can get temperature information from?
Questions
1. Has anyone here had this issue and resolved it?
2. Am I right in thinking that if the OBD looks okay, the MAF is okay?
3. Is there anything else I should be checking out in the OBD? For example, what should the O2 sensors be reading? What are some normal MAF values?
4. Is my logic about the ECU correct?
5. If the ECU is "bad," does anyone have any idea what about it goes bad? I have a lot of hands-on electronics experience, so if it's just some cap or relay that goes bad, I have no problem with taking that sucker out and fixing it.
6. I've also heard someone mention that this could be an issue with the fan clutch..? i.e. the fan only has one speed right now because the clutch has failed. How would I go about testing it?
7. Any other ideas about what might be wrong?
Thanks for your help!
08-10-2014, 09:59 AM
#4
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2002 SLK320
Radiator Cooling Fan
On my 2002 SLK 320, Replaced the Temperature Sending unit and this did not solve the problem. The direct input to the Fan is a Control Module and looking at this next. However this module is not cheap and i have heard from other that replacing this module did not solve the problem. It would be great if someone could come up with a solution and post it. If Ido will post!
09-05-2014, 11:42 AM
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2002 slk 200k
www.youtube.com/watch?v=NT8aSUCT50s
09-25-2014, 09:08 AM
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2002 slk 200k
My problem was slightly different when the car is turned off the fan would start up after 5sec and blast full speed non stop till the battery was drained completely. I managed to sort this problem out by replacing the fan controller. alu box with two thick wires and two thin ones. my reservoir bottle light also came on.
