406 HDi: Message "Coolant too hot"

[marsalek]

Dear Guys,

my father's 406 HDi 109 BHP, Mk2 prints a message "Coolant too hot" and beeps, although the engine temperature is fine, e.g. immediately after cranking up a cold engine. The coolant thermometer stays always below 90 degrees. The thermometer gives believable readings, so the "coolant too hot" message is somewhat ill.

The message comes ONLY WHEN THE AIRCON IS ENGAGED. Any ideas? Tha aircon works fine, it has been refilled after it started printing the stupid message, but the situation has not changed. The engine cooler fan engages as soon as the aircon is switched on.

What shoul I check? Is it a common/known issue?

Thanks a lot in advance
Karel

[Peter.N.]

I don't have a clue and neither does anyone else apparently, I would have said a faulty sensor but the fact that it only does it with the aircon on rather suggests that it isn't although doesn't eliminate it. Its obviously some electronic gremlin but if the car is all right otherwise and drives OK I wouldn't worry about it, its likely to be expensive to diagnose.

Peter

[marsalek]

Dear Peter,

thank you for your kind reply. In the meantime I got a hint from a German forum. A couple of guys reported the same symptoms when one of two resistors for the engine cooler fan was burned. The resistors are in series with the fan and define the fans speed, controlled over three relais. Actually not the resistors itself but the thermal protection fuse get burned, so one can replace only the "fuse" (located inside the resistor block), when you find out the temperature ratings.

Regards
Karel

[Northern_Mike]

I seem to recall this happening on a Picasso I put the lexia on for a friend at work. I'm sure it was one of the coolant sensors. I think I tested all the fans on high and low speed, and they were ok, but they were getting an overheating message almost instantly on start up. I think it was the coolant sensor in the head.

[marsalek]

I seem to recall this happening on a Picasso I put the lexia on for a friend at work. I'm sure it was one of the coolant sensors. I think I tested all the fans on high and low speed, and they were ok, but they were getting an overheating message almost instantly on start up. I think it was the coolant sensor in the head.

Dear mike,
was the behaviour related to the aircon on/off as it is in my case?

Regards
Karel

[marsalek]

Hi guys,
we can close this thread. I found the fault. The resistor for the slow speed of the engine cooler fan was burned. Not exactly the resistor itself but the thermal fuse that is in series inside the resistor assembly. The thermal fuse blew itself as its terminals got hot due to lose contacts. As soon as the engine ECU wanted to switch the fan to the low speed, the fan stopped working and we got the message "Coolant too hot" and the medium speed was engaged within a second or two. So quite fail proof design

Thanks for your help
Karel

[patrickgledhill]

Hi Guys, I have had the exact same problem and the fan relay solved it. Glad you got it sorted
Pat