Hello Rednal mate.
Interesting readings -
Can I confirm a couple of thinks though -

REDNAL3 said:

With the ignition OFF the resistance (ohms / Kohms) between the two terminals of the PLUG is 1.028

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Can you confirm that is 1.028 Kohms (1028 ohms) ? the meter should show a 'K' depending on the make.

REDNAL3 said:

With the ignition OFF the resistance (ohms / Kohms) between the two terminals of the actual sensor 2.28 and coolant temperature at time 26 degrees

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Same above - please confirm that this is Kohms ? - I am sure it is...
Also, can you confirm the engine had not been running therefore the water in the system was presumably at ambient temps (26C ?)

Joe

Joe_H said:

Hello Rednal mate.
Interesting readings -
Can I confirm a couple of thinks though -

Can you confirm that is 1.028 Kohms (1028 ohms) ? the meter should show a 'K' depending on the make.


Same above - please confirm that this is Kohms ? - I am sure it is...
Also, can you confirm the engine had not been running therefore the water in the system was presumably at ambient temps (26C ?)

Joe

Click to expand...

Also, where did you get the replacement CTS from ?
(the most important thing I need to know at this time is that the 26C coolant temp was based on engine not been run and ambient temps outside !- very important!)

Joe

Hi yes car was left overnight and only taken round block (1 mile max) about 3 of hours ago. It was 15 degree first thing this morning before going round the block. When I came back it was about 31 degrees and when I carried out those tests about 3 hours later it was 26 degrees.I have attached pic of my t ester

The replacement sensor was from Eurocarparts and the brand was Haas. They supply parts by cross checking registration number.

This is really important re the coolant temperature - I wish you had measured the sensor resistance before driving it anywhere.
That reading for the sensor indicates a coolant temperature of around 60C not 26C.
HOWEVER - because you have driven the car it is very difficult to be certain as the engine can act as a huge heat storage source.
Also, that kind of reading would not cause a starting issue - meaning - if you went out now and tried to start it - it should start fine as it thinks it is at 60C.
(default failsafe with no sensor is 80C.)
Does the engine even feel warm to the touch (warmer than ambient for example) ?

Having driven it it is confusing the issue as to known accurate coolant temps - also under-bonnet temps can be higher in the sunshine and also maintain heat more after driving - even only a mile on a warm / hot day. !

Do you have access to the vehicle now or are you working ? - we need two readings of the resistance across the CTS (plug removed of course - just the resistance of the sensor) - - one when the engine has stood overnight - without starting it first !- and one when it is up to normal operating temperature. ( according to what you have said when warm it will not start properly)
The reading after overnight prior to any starting - should be taken and ambient noted. Then drive it until the engine is fully up to temperature on the gauge, then check the cts resistance again.

Sorry, but by driving even a small amount I cannot rely on those figures.

It is quite possible that the coolant IS still at around 60C hard to tell after being driven even a short amount on a hot day.
If you take those readings as I suggest - first thing in the morning and then when fully up to temp on the gauge - it will be meaningful. If you are trying to do it while going to work - for example - then it needs checking before start in the morning - then driving far enough (even if it means going a lot further than normal!) to get if fully up to temp and then check again.

It cannot be half measures unfortunately - check when stood overnight - then when up to normal temp. if you have to - drive it around UNTIL it gets fully up to normal temp on the gauge in the car.

I must stress this again -This is really important - we are basically left with 2 possible diagnoses - first is the cts itself (not convinced yet - and - the problem did not improve with replacement) and second is the ECU.
Only those accurate reading will tell.
Joe

You can ascertain if the new and old sensors give different resistances easy enough. I would put both sensors in the same location, like the kitchen for an hour so that they stabilise with each other. Then measure the resistance of both. Assuming the kitchen is about 23°C you should see a resistance of around 3.8 K ohms.
A wildly different resistance between them, could well be your issue. If they both measure similar readings at room temperature, try submerging both in a pan of hot water. Let them stabilise for a few minutes, then measure the resistance again. I would think that 2 K ohms would be about right for hot tap watet. Again you are looking for wildly different resistances.

Ok will get those readings. I'm at home on holiday for a few days.
The outside temperature here is only about 15 degrees (unfortunately).The engine is not warm to touch at moment and coolant temp is now 18 degrees.
The car will take multiple attempts to start if coolant temp is above 15/16 degrees. If I remove coolant sensor plug it will start every time regardless of temperature.

Hi Nodge, the issue was there before the new CTS - it did not change with a replacement which is highly unusual - there is also a table for resistance v temp included in this thread. I agree that the sensor can be tested out of the vehicle no worries, however, it can also be tested really simply by the tests I said - checking it after standing overnight (It cannot be more than ambient at that point!) and then again when fully up to temp) - that test can be done on one single journey in about 15 minutes depending how long it takes to get up to temp.
I do not, at this stage, think this is a cts sesnor issue - and again, the checks either on the car or off will tell. It is easier ON the car to be honest. ! - just dont drive it first to confuse things .

As you have a TD4, you could perhaps do a quick test for me ? - remove the cts plug - ignition off - measure resistance across the plug terminals (not the CTS) - the cts resistance is useful if you know the temps - ie stood overnight or fully up to temp.
Measuring across the plug ignition off helps by checking the resistance of the lower resistor in the potential divider in the ECU. - it is not definitive but his is about 1k which is possibly / probably normal.
Also, with the ignition on and plug disconnected, measure the voltage across the terminals of the plug.
The TD4 system uses the 'reference' voltage from the centre tap of a potential divider in the ecu - this voltage will be fixed with the plug disconnected - but will vary according to temperature when connected to the cts - as the cts and bottom resistor of the potential divider are then in parallel - would be useful to compare.
Joe

REDNAL3 said:

Ok will get those readings. I'm at home on holiday for a few days.
The outside temperature here is only about 15 degrees (unfortunately).The engine is not warm to touch at moment and coolant temp is now 18 degrees.
The car will take multiple attempts to start if coolant temp is above 15/16 degrees. If I remove coolant sensor plug it will start every time regardless of temperature.

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How are you determining the coolant temp at 18 degrees at the moment mate ?
If you are sure it is below 20C then what is the cts resistance reading now then please ? - with you being at home we can probably determine the issue now.
Joe

I knew it was 18 as I had just checked it with the i930 tool before last post. I briefly cranked it once at same time to see if it would fire up but as expected it didnt.
The resistance between plug terminals right now is 2.96 and the coolant temperature is 19.1.

REDNAL3 said:

I knew it was 18 as I had just checked it with the i930 tool before last post. I briefly cranked it once at same time to see if it would fire up but as expected it didnt.
The resistance between plug terminals right now is 2.96 and the coolant temperature is 19.1.

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19°C should read as over 4K ohms not 2.96.
2.96 should show a live temp of around 50-60°C.
It looks like the potential divider in the ECM could be screwy.

Nodge68 said:

19°C should read as over 4K ohms not 2.96.
2.96 should show a live temp of around 50-60°C.
It looks like the potential divider in the ECM could be screwy.

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First off - to Rednal3 - I presume you mean the resistance of the CTS terminals - not the 'plug' terminals as you wrote ? (that is with the plug disconnected of course ?
2.96 is about 45C on the chart from Rave. - that would indicate a very strange thing...
Firstly - IF the chart in Rave is correct - then the CTS is screwed - not the ECU .
However - it then begs the question of - where the Feck does the i930 read it's cts from ????

Hi Nodge The 2.96 is the resistance between the sensor terminals not the plug

REDNAL3 said:

Hi Nodge The 2.96 is the resistance between the sensor terminals not the plug

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Well, the plot thickens - I have definitely checked rave again - page 124 under EDC CTS.... the chart is the correct.one definitely for the EDC (TD4).. so, how the hell is the i930 reading the bloody CTS (unless of course the RAVE chart is incorrect.....)

Nodge, are you in a position to check your cts sensor resistance in relation to perceived temps ? - this is crazy...

Rednal3, in the picture of the meter you posted, you had it set to 2Kohm range - try the test again with it set to 20Kohm range (it would appear your meter is selectable 2K 20K 200K )- I am sure it will make no difference - but ---- ........................................

Yes I had tried that setting first and it doesn't read anything at the 2k option.It just remains at 1.
Once I select 20k I get the readings.Right now its sitting at 3.08 and coolant temperature is 19.05 degrees

Have you local store that you can get a sensor from ? - one that you can take your meter with you ? - you can measure the resistance of the sensor at room temperature and it should be about 4K ohms. if it is then you have the wrong one fitted. I am still baffled by the i930 reading though - it does not make sense. I am wondering if the chart in RAVE is wrong ???

BTW, there is nothing added to this engine is there - ? - no 'remap' no 'magic box' 'performance increase' device ?

The old sensor was in my jacket pocket in shed outside. The temperature outside is 14 degrees and the resistance between terminals on this one is 2.44

is there a part number on that cts ?

I put the tip of sensor in boiling water and resistance reading went to 0.00. I removed it and Its been cooling down rapidly for past few minutes. It is no longer warm to touch and is now reading 1.62
Its a BMW part The part number bmw 1433076