K-series water temperature sensor.

[BigBen]

The fan on my k-series (1.8 VVC) has stopped coming on even at high (105deg temperatures) so far I have tried the following:

- Disconnect the temperature sensor to the ECU, this causes the fan to come on as expected thus showing the relay, power supply and ECU are ok.

- Changed the sensor twice once for a used unit I had 'in stock' and the second time for new one. The fan still does not come on with temperature.

The combination of these two tests suggests that the ECU, wiring loom and logically the sensor are all ok but they don't work in combination. Any suggestions as I am running out of ideas.

My only remaining thought is that that of the two wires from the sensor to the ECU one could be broken / causing high resistance so making it impossible for the sensor to trigger the fan.

Cheers

Ben

[stevieturbo]

How are you measuring this temperature ? In dash gauges tend to be very innaccurate.

Although if the fan had previously been on at the same position, it could be a concern.

Any mechanic with diagnostic equipment would be able to see if the ecu is getting the proper temperature signals though.


Although the fact that when you unplug the temp sensor the fa comes on...does suggest the ecu does still have the ability to operate the fan.

[dan19evans]

loose/corroded wiring connection ?

surely any bad connections would affect the voltage input to the ECU, so the ECU may be sensing that the engine is colder than it is ?

Edited by dan19evans on Saturday 3rd July 01:24

[Justin S]

don't know if it is the same as a Lotus VVC, but the blue sensor does feck all (literally) and the black sensor runs the dash temp, ecu and the fans............which one are you dosconnnecting? Is there 2 ?

[Mr2Mike]

Air lock? If the cooling system is not bled properly (and it can be fiddly on the mid-engined installs), then the sensors can incorrectly indicate a lower temperature.

Edited by Mr2Mike on Sunday 4th July 13:50

[BigBen]

Justin S said:

don't know if it is the same as a Lotus VVC, but the blue sensor does feck all (literally) and the black sensor runs the dash temp, ecu and the fans............which one are you dosconnnecting? Is there 2 ?

Should be the same but has a brown and a blue sensor, the blue one only does the dash and the brown the fan. Of course the problem could be with the blue sensor giving over readings to the dash giving the impression it is hotter than it really is, however the conditions involve make me think the fan should be coming on based on past experience.

Knackered wiring would be a good shout, shame as it is not necessarily easy to mess about with even given the open nature of the Atom.

Next thing I will try (as its next easiest) is measuring the resistance of the sensor as it heats up and confirm 'vs some plots of expected values I have seen on the web.

Cheers

Ben

[BigBen]

Had a bit more of a play around today (finally) and noted the following:

-Made a jig up to vary the resistance fed to the ECU and can make the fan turn on and off at expected voltages. This also proves the wiring from the sensor to the ECU.

-Measured the resistance of the temp sensor as the engine warmed up and it was as expected.

Therefore I think whoever suggested that dash temperature gauges are wildly inaccurate could win the prize here, but am I brave enough to run it to 115 deg to find out.......

Ben