Mischievous violet / purple radiator wire and a ECM-6110 (engine cooling fan relay - signal missing)

Post by **- Pete -** » 21 May 2026, 22:15

This is on my wife’s 376,000 mile 04 XC70.
I replaced the original radiator (blue box actual Volvo part), because it got a hole, replaced the heater core for the same reason.

I noticed it running hot on a few occasions over this past winter. Now that temperatures are warmer, it seems to want to run hot more frequently. I also noticed that the cooling fan does not seem to kick on. Verified with Vida that the ECM is calling for the fan, but the fan does not kick on. Tested a known, working fan on this vehicle and again, the fan did not kick on. Tested the fan out of the vehicle this thread is about on another vehicle and the fan did work.

What I am asking is this; is it most common that the purple wire is broken at some point between the fan connector and the ECM? Also, if it is typically a wire problem, where is the most common junction where this failure occurs? Or is it most commonly a fault within the ECM itself?

Thanks for your time everyone, can’t tell you all how much I love and appreciate this place.

Post by **jonesg** » 21 May 2026, 22:49

yes, a signal tracer or fox and hound, can trace signal along its length to the break. $25 amazon.
https://www.amazon.com/VDIAGTOOL-V210-A ... 209&sr=8-7

Post by **- Pete -** » 22 May 2026, 00:00

jonesg wrote: 21 May 2026, 22:49 yes, a signal tracer or fox and hound, can trace signal along its length to the break. $25 amazon.
https://www.amazon.com/VDIAGTOOL-V210-A ... 209&sr=8-7

Yeah…you pretty much rock Gerard. Can’t thank you enough. That will surely streamline my efforts immensely. Thank you so much!

: IMG_3309.jpeg (45.21 KiB) Viewed 1464 times

Post by **vtl** » 22 May 2026, 04:54

Did you check the relay and fuse?

Post by **- Pete -** » 22 May 2026, 06:54

vtl wrote: 22 May 2026, 04:54 Did you check the relay and fuse?

I looked for one that coincided with what was talked about out online and listed on the fuse panel lid but ultimately I found out that “the relay is built into the power module on the backside of the fan…” according to my research. Is that incorrect?

Post by **vtl** » 22 May 2026, 07:16

- Pete - wrote: 22 May 2026, 06:54
vtl wrote: 22 May 2026, 04:54 Did you check the relay and fuse?
I looked for one that coincided with what was talked about out online and listed on the fuse panel lid but ultimately I found out that “the relay is built into the power module on the backside of the fan…” according to my research. Is that incorrect?

You have to remove the upper panel in the fuse box, the relay will be under it. A bunch of screws and fighting with plastic catches.

Post by **jonesg** » 22 May 2026, 07:20

Early models had external relay, yours is molded into the module on the fan.

note, I snipped the violet wire near the headlight because I didn't want to back feed voltage into the ecm, disconnected battery too.
I don't like messing with the electronics on this car at all.

a coat hanger soldering clip helps hold the wires for soldering, i used heat shrink and liquid tape to seal the joint from moisture.
its an awkward position, you can only get one hand in there.

Post by **jonesg** » 22 May 2026, 07:29

The relay in the power distribution box is for the 12v feed, if you detect 12v at the fan plug its good, ..... I think.
Vs the signal switched relay in the onboard fan module.

Post by **- Pete -** » 22 May 2026, 07:45

vtl wrote: 22 May 2026, 07:16
- Pete - wrote: 22 May 2026, 06:54
vtl wrote: 22 May 2026, 04:54 Did you check the relay and fuse?
I looked for one that coincided with what was talked about out online and listed on the fuse panel lid but ultimately I found out that “the relay is built into the power module on the backside of the fan…” according to my research. Is that incorrect?
You have to remove the upper panel in the fuse box, the relay will be under it. A bunch of screws and fighting with plastic catches.

1.jpg

2.jpg

Yeah I did see that FFM8 listing but in all the years I’ve been wrenching on Volvos never once realized there was a 2nd level to that fuse block! I’ll have to check on that. My fan is the style that has the power module molded into the rear by the way.

Post by **vtl** » 22 May 2026, 07:48

- Pete - wrote: 22 May 2026, 07:45 Yeah I did see that FFM8 listing but in all the years I’ve been wrenching on Volvos never once realized there was a 2nd level to that fuse block! I’ll have to check on that. My fan is the style that has the power module molded into the rear by the way.

The "forever" fan, with brushless motor. Either that 60A relay is cooked, or ECM.