Code 27B8

[randrews15]

I got a over heat warning today with code 27B8. Luckily, I was stopping as the alert came up and it was actually cold here in Florida. Drove home after several hours without an issue and no alert. Using ISTA I got code 27B8, cooling fan not functioning. There seems to be limited information on this. I used ISTA to activate the fan and no joy. Using an electrical tester I have 12 volts at the harness, good ground, and almost 5 volts with the fan is requested to come on at the signal wire. I even tried turning the air on and it does not turn the fan on. Also, the fuse is good. Has anyone else experienced this? I suspect it’s the fan and even tried to jump it with no luck. The fan is $1000 and want to make sure I’m not missing something else. Thanks for any help.

[yardbro]

Your troubleshooting looks good so far. I have attached the wiring diagram for the electric fan, but you have probably seen it already.

If you can be absolutely sure that your power and ground can carry a load (not just show 12v and a path to ground with a multimeter) then you aren't missing anything in terms of what that fan needs to run. Battery voltage at all times via terminal 30, ground, and a relay signal from the DME.

Just to be thorough before you condemn a pretty expensive fan, trying to pull at least 5A on the main power and ground feeds just to be sure they are actually solid under some load. If you find these to be okay, it's time to look for a new fan :/

[Scrippy]

Fuse checked out I see. I’d check the relay. I’d also just apply 12VDC to the fan itself and see what happens.

[CTMike]

Doing this from memory at the moment and will dig a little more… when I picked up my M3 a few years ago, turns out the fan was on its way out. Shop replaced the fan… but things still didn’t work. There’s a fan relay under the passenger footwell if I recall…ultimately, they followed the trace back all the way back near the battery and had to re-solder… their thinking was along the lines of it being due to excessive current draw as the fan was failing. Ultimately got it working and no issues since.

[randrews15]

Originally Posted by Scrippy

Fuse checked out I see. I’d check the relay. I’d also just apply 12VDC to the fan itself and see what happens.

I did use a power probe to try to activate the fan and no such luck. I am assuming the relay is still good since when I use ISTA to activate the fan I see the draw on the signal wire goes up to 3.5 volts and then drops back down when it’s done.

[randrews15]

Originally Posted by CTMike

Doing this from memory at the moment and will dig a little more… when I picked up my M3 a few years ago, turns out the fan was on its way out. Shop replaced the fan… but things still didn’t work. There’s a fan relay under the passenger footwell if I recall…ultimately, they followed the trace back all the way back near the battery and had to re-solder… their thinking was along the lines of it being due to excessive current draw as the fan was failing. Ultimately got it working and no issues since.

I hope I don’t have to go digger deeper. I found it interesting there’s no information as to how much voltage the signal wire can put out. As I look back, I do recall seeing the fan turning on and off the other day while idling in the garage. I thought it was weird but just dismissed it. The A/C was on which should have it running all the time. I suspect the fan was on its way out and just went. I am curious to where they had to do the wire repair. It seems like this isn’t a common problem.

[randrews15]

The best part was the instructions in ISTA was very plain for checking the fan.

1) check wiring at fan.
2) replace fan if wiring appears fine.

I’d like to seem some specs on the signal wire for voltage to confirm it’s within spec.

[pirategenes]

Seems like this is pointing to the fan motor as the culprit. You can probably save some coin by swapping in the E60 535i fan blade and motor assembly. Idea from this Sal's Garage DIY YouTube video:

[CTMike]

Originally Posted by randrews15

I hope I don’t have to go digger deeper. I found it interesting there’s no information as to how much voltage the signal wire can put out. As I look back, I do recall seeing the fan turning on and off the other day while idling in the garage. I thought it was weird but just dismissed it. The A/C was on which should have it running all the time. I suspect the fan was on its way out and just went. I am curious to where they had to do the wire repair. It seems like this isn’t a common problem.

Here’s what I had noted at the time… get you a little closer: “They inspected the fan circuit again and found an overheated contact by the rear fuse carrier, near the battery.”

[randrews15]

First, I wanted to say thanks for everyone’s input as it was a great help. After digging around and checking wiring again I found the culprit. The signal wire on the fan side of the connector was loose. There is no real retaining clip with some wires. I could tell since the weatherproof seal was about half way out when I went to check voltage on that side of the terminal. After re-seating it the fan came back to life and functions as it should. I can only suspect that when I unplugged it to replace the upper coolant line that it became dislodged. The lesson here is check the wire when plugging the connector back together. Now to put the car back together.

[Kross]

Sorry to dig up an old post but this one has been most informative so far so I'm hoping for some help with a similar problem.

08 e90 m3 + ESS VT595 + do88 big pack

I'm looking for help diagnosing and fixing my radiator fan not kicking on, causing overheating at idle.

I'm only getting 7 volts to the fan plug with the car running and AC on full blast - I blieve I'm supposed to be getting continuous 12v.

I've checked fuse 88 behind the glove box. Looks ok, a little corrosion, gett 12v+ on both leads.

Not really sure where to go from here, any help is appreciated!

[yardbro]

Originally Posted by Kross

Sorry to dig up an old post but this one has been most informative so far so I'm hoping for some help with a similar problem.

08 e90 m3 + ESS VT595 + do88 big pack

I'm looking for help diagnosing and fixing my radiator fan not kicking on, causing overheating at idle.

I'm only getting 7 volts to the fan plug with the car running and AC on full blast - I blieve I'm supposed to be getting continuous 12v.

I've checked fuse 88 behind the glove box. Looks ok, a little corrosion, gett 12v+ on both leads.

Not really sure where to go from here, any help is appreciated!

Please clarify which pin you are measuring this at, and what state the vehicle is in when you're measuring. The cut-out relay for the fan is generally not energized with the key off and the vehicle asleep I believe. Make sure ignition is on to be safe.

There should be 3 wires there at the fan plug; Brown is ground, red is battery +, and I think blue, which would be the duty cycle control wire. If you're seeing 7V on the red wire with absolutely no load and only your multimeter then, yeah, you have a problem there.

[Kross]

Originally Posted by yardbro

Please clarify which pin you are measuring this at, and what state the vehicle is in when you're measuring. The cut-out relay for the fan is generally not energized with the key off and the vehicle asleep I believe. Make sure ignition is on to be safe.

There should be 3 wires there at the fan plug; Brown is ground, red is battery +, and I think blue, which would be the duty cycle control wire. If you're seeing 7V on the red wire with absolutely no load and only your multimeter then, yeah, you have a problem there.

Thanks for the feedback. I was measuring between the two primary (red and black/brown) wires, not the signal. I found the issue - the 150A relay, found under the carpet in front of the passenger seat, had failed due to moisture. Replaced it and the fan's working again.

[Brandoch]

Originally Posted by Kross

Thanks for the feedback. I was measuring between the two primary (red and black/brown) wires, not the signal. I found the issue - the 150A relay, found under the carpet in front of the passenger seat, had failed due to moisture. Replaced it and the fan's working again.

Fan......tastic!

[yardbro]

Originally Posted by Kross

Thanks for the feedback. I was measuring between the two primary (red and black/brown) wires, not the signal. I found the issue - the 150A relay, found under the carpet in front of the passenger seat, had failed due to moisture. Replaced it and the fan's working again.

Excellent work. Thank you for the update.