CTS and ATS question

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_kid_
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CTS and ATS question

Post by _kid_ »

My xantia is good with the exception of terrible fuel consumption. I believe its around 3-4 miles per gallon less than what it should be. All the usual things have been looked at, it has flown through the emissions on 3 mots (inc one last week) so im happy it not lamada related. Also brakes are spinning fine, filters all new. No fuel smells either.

I have put a new coolant temperature sensor on but no difference. I have measured the ohms on the CTS and also the air temperature sensor (which is original AFAIK) and am getting different readings. With the engine around 80c, the cts was around 400 ohms, whilst the ats was 1200 ohms, i believe the cts is showing a good reading. Is it normal for such a large variation in figures?

The one clue i have re consumption is the engine management light stays on for 5 seconds after the engine is started and then extinguishes, whereas i believe it should go off immediately, would it be possible the ats is not fully functioning but still the ems will operate albeit at a self determined less efficient level, and therefore keep the ems light off.

I am going to get a diagnostic reading soon, but would like some advice anyhow.
currently no citroens :-(
1.4 2000 forte now gone too
xantia 1.8i 16v dimension 1996P now gone,
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AndersDK
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Post by AndersDK »

Hi kid -

Both the ats and cts are standard NTC resistor elements - i.e. generic sensors. They even operate over the same ohmic value range.

The ohmic value varies greatly - i.e. there is nothig like "56.5degC = 1012.8 ohm" - not at all.
Its more like "56.5degC ~ approx 1000 ohm +/- 25%".

The NTC resistor element has a very large ohmic value variance over its temperature range - so its pretty useful to determine whereabouts the sensor value is in terms of engine operating conditions.

As a rule of thumb these sensors varies from approx 5000ohm/0degC down to approx 300ohm/85degC.
For testing purposes - you can always short out the sensor leads to signal the ECU "its hot here". Or the opposite : you can always remove the plug/leads from the sensor to signal the ECU : "its darned cold here".

NOTE : the ats senses the intake/manifold AIR temperature. As the air is constantly flowing in and renewed - it will always be at ambient temperature - like the air you breathe. Unless the engine stalls of course - then the ats temp will raise to the manifold temperature.

Conclusion : the sensor values you have read out are fully normal - not indicating anything else than they work as supposed to.

If the engine light stays on - it may be its trying to signal about stored error codes. Have you tried get the fault codes read out ?
Last edited by AndersDK on 26 Jul 2006, 21:35, edited 1 time in total.
Anders (DK) - '90 BX16Image
_kid_
Posts: 206
Joined: 07 Oct 2005, 07:05
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Post by _kid_ »

Thanks anders, a full explanation as always :)

I have checked the sensors now, when the engine was slightly cooler and sure enough the reading have increased on both sensors by around 400 ohms, so guess there are doing what they are supposed to- i wanted to be sure the variation of readings was acceptable- obviously it is then.

Re the engine man light, i think that’s worth a go as i cant thing of anything else to try.
currently no citroens :-(
1.4 2000 forte now gone too
xantia 1.8i 16v dimension 1996P now gone,
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