Cooling fan only works when coolant sensor unplugged 1.6HDi

[xsara92]

Hi,
I know there have been other threads about this, but hopefully this is worthy of a new one...
I've tried to diagnose a inoperative radiator fan on my 1.6HDi 16V. 2005 plate. Xsara Picasso Exclusive with fully automatic climate control.
Finally a breakthrough. Unplugged the coolant temp sensor with the engine on. Hey presto, fan unit does work! A YT video gave the pointer...
So, this would implicate the relay(s) that control the fan switching as I understand. Is this the only possibility?

Edit: Fan has never come on when A/C is on car stationary.

Possible other gremlins, however suggest:
- Fan did not switch off with ignition. Didn't want to wait and see if it switches off, in case I drained my battery. Should I test?

- I get the MIL light occasionally when pushing the engine, e.g. up long gradual hills at 40-50mph in uplands, or when full boost (overboosting?), the car has cruise control and using the "pause/play" button seems to WOT the engine to resume a high speed triggering MIL.
However the dash guage has never shown engine temp above the 3 bars.
So I want to know if the ECU detecting fan not working can give MIL with this design?

The A/C is working to a degree, enough to demist windscreen but not to cool the car recently when its like 20-25C outside and humid.

Last thing, I was surprised that when I finally got the fan on, it seemed like the min speed, as was really quiet...but I thought the failsafe design switches it on to max speed which is loud.

[mickthemaverick]

You may find the info in this link useful for clarification of your problem:

https://xerodrive.com/auto-guides/coola ... -it-fails/

[xantia_v6]

You really need to get the engine ECU and BSI scanned for fault codes and check the live data, as it is the engine ECU that interprets the signal from the temperature sensor and decides whether to run the fan, it interacts with the BSI ECU to handle cooling when the A/C is switched on.

[xsara92]

Thanks both, is there a reader someone can recommend for this level of scanning?

[xantia_v6]

All modern readers will do the engine ECU, and most will do the BSI. For other things like entertainment systems, it varies, so best to check or ask the supplier.

[xsara92]

Looks like I need a Lexia!