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Radiator Fan turns on HIGH and randomly on/off after when car is off
Hi All, 2010 E350 4matic - 130k miles (my dad's)
Issue basics:
all it takes is opening the car with the car keys and the radiator fan kicks in on HIGH.
Turning key to ON position alone triggers the radiator fan to run HIGH as well as turning the car on
when the car is off the radiator keeps going on high for few minutes then turns off.
when car is off, the radiator fan also keeps going on and off for few minutes randomly
I checked the relay that activates it (which is N in the front driver size box). i can hear the relay clicking, then the radiator kicks on for few minutes, relay kicks off and radiator fan stops. this repeats every few minutes.
we did have a huge storm come thru the night before this happened (not sure if this effected anything? ECU maybe?
any ideas what this could be? right now i'm getting down to ECU issue. The only thing that i'm about to check tomorrow morning is the coolant temperature sensor has oil that dripped on top of the connection from last oil change my dad attempted and overspilled oil while changing the filter. I'm going to take that our clean it tomorrow morning and put it back on as well as check all connections.
Anything else i should check? you're input is much appreciated.
You need a decent bi-directional scanner to speed up the troubleshooting and verify a few things.
There are a few "commands" which can make a fan go HIGH speed where it was not supposed to do so.
You had a huge storm, but was the car parked outside and get the fury of rain and wind ?
If so, water leak into car can cause lots of problems with electric stuff, when and if the wet areas are electric sensitive one.
Thank you, i'm also going to run the scanner on it tomorrow. i have the icarsoft MB II scanner. hopefully that will have enough options to troubleshoot it.
The FAN command is done by to N3/10 or Engine Computer, not HVAC computer N22/7.
Among others which can cause FAN to go maximum speed or 90% duty cycle ( OFF is 10% duty cycle ) , are :
01. Defective coolant temperature sensor, be it shorted or reading VERY HOT erroneously
02. High pressure of HVAC refrigerant, usually when at engine off for say 10+ hours or complete cool down, you then read the pressure of R134A being 20BAR, that can trigger the cooling fan maximum speed.
The normal pressure for R134A is temperature based ( after car cool down back to ambient temperature ). See here : https://www.igasusa.com/pt-charts/R134A-PT-Chart.pdf
The AAC N22/7 HVAC computer has this data.
03. The ambient air temperature sensor, the one at the bumper. This could be a culprit, but not a strong suspect.
Thank you for that feedback, i scanned it last night and here are the 7 codes i'm receiving that has when i went into the radiator fan options. i'm currently looking them up to see what to look for but maybe someone here can guide me if they understand them better. Remember the car doesn't have a check engine or any kind of light normally. It seems to me that it's saying the radiator fan has shorted?
i was told by a mechanic just by talking on the phone that it's most possibly the coolant sensor and to change that first, but can a coolant sensor really do this?
Out of the 7 codes, only 2 are current. Would you mind erasing the DTC codes (you already took pictures anyways), and restart the engine to see what new shows up?
I don't think your temp sensor is involved this time.
My clue is none of the codes point to sensor...
So to me this mean, sensor is likely off the hook for now but we keep it mind to go read its data PID - Nice & simple troubleshooting - no wet finger guessing for divers
big clue!
When you consider the string of DTC faults... they involve the fan. That's a call to focuss on testing it.
I translate "... short circuit to positive" as bad GND circuit!
The next step is to locate fan GND and clean it better than factory new.
Please take before & after pictures for us.
Do remove power before dealing with live 100Amp circuit
Last edited by CaliBenzDriver; Aug 2, 2023 at 01:21 AM.
thank you guys for the nice points so i got working again on it today and here are some more screenshots. here is what i did
1. checked fuses and relays and all seem good.
2. i reset the DTC codes above and only 2 came back on (see pictures below)
3. i decided to look more into the data while car is running and found that the coolant temp is running pretty high - around 125 celcius, from what i'm finding it's supposed to be from 80-100.
4. last thing i notice is that i don't beleive the fan is getting the signal to go high but it's still going to 90% but again correct me if i'm reading this wrong.
correct me if i'm wrong but this tells me that temp sensor is working. specially that i see it going up and down few degrees. or could a sensor be reading wrong?
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I read a while back if the fan doesn't get a signal from the ECU the fan goes into high mode like you have.
Would disconnect the fan plug and give it a clean, reinstall it and see if that does anything as an easy test.
Even better to check the fan 4 pin plug for proper inputs.
You seems to have 2 issues.
01A. If indeed your coolant temp sensor is correct and read 127C, that is already overheating and I believe it should have triggered overheating which if I remember correctly is 125C.
01B. You may have a coolant temp sensor drifting its value and seemingly 127C while it is not......... well this thermistor will drift overtime and bye-bye.
02. It seems you did not get the 10% duty signal from ECM to fan controller module, hence FAN module will give 90% or full power as safety measure.
This 01 and 02 will produce the same maximum speed fan command at 90% duty cycle or emergency step is probably a better description.
Try to tell us per every photo, which module produce those DTC ?
Those DTC does not exist in MB modules...... A10D1 at least. There is no "A" as far as I know in DTC list.
Like this one : Starts with P or what ? There is no P2357 in my engine computer DTC list
Why can't iCarsoft simply follow MB DTC like all others ???
thank you for the feedback, it's my fault as i should of listed where i clicked to get to those, most had to do with fan controls but first one that has the A was part of something that had to do with power i believe. i'll recheck and let you know.
This car is for my dad and unfortunately he doesn't have time to keep waiting on me to troubleshoot so he took it to the shop to get it looked at, i'll update everyone here what they find out. i'm sure they will figure it out. i'm hoping it's not the ECU and that's why i'm helping him troubleshoot it.
some more info from yesturday i did find out that the AC pressure was on near 80-90 psi and i brought it down a bit but not all the way to the specs. i did read on some threads that this can be the cause but it didn't make a difference.
I'll keep you updated on what we found out on solution
thank you for the feedback, it's my fault as i should of listed where i clicked to get to those, most had to do with fan controls but first one that has the A was part of something that had to do with power i believe. i'll recheck and let you know.
This car is for my dad and unfortunately he doesn't have time to keep waiting on me to troubleshoot so he took it to the shop to get it looked at, i'll update everyone here what they find out. i'm sure they will figure it out. i'm hoping it's not the ECU and that's why i'm helping him troubleshoot it.
some more info from yesturday i did find out that the AC pressure was on near 80-90 psi and i brought it down a bit but not all the way to the specs. i did read on some threads that this can be the cause but it didn't make a difference.
I'll keep you updated on what we found out on solution
I am having the same issue where you able to find it?
thank you for the feedback, it's my fault as i should of listed where i clicked to get to those, most had to do with fan controls but first one that has the A was part of something that had to do with power i believe. i'll recheck and let you know.
This car is for my dad and unfortunately he doesn't have time to keep waiting on me to troubleshoot so he took it to the shop to get it looked at, i'll update everyone here what they find out. i'm sure they will figure it out. i'm hoping it's not the ECU and that's why i'm helping him troubleshoot it.
some more info from yesturday i did find out that the AC pressure was on near 80-90 psi and i brought it down a bit but not all the way to the specs. i did read on some threads that this can be the cause but it didn't make a difference.
I'll keep you updated on what we found out on solution
I have exact same issue and car, just walking near car and the fan comes on full speed, anybody know what the solution was? I am also getting a random grey temp alert on dash info.
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