Hi Well bear with me 
... I did disconnect a temp sensor previously when Nodge suggested it could be a possibility. It didn't make difference unfortunately and rather than buy a new one I had worked on the assumption that the ecu would input a default reference which kind of ties in with comment above. However its now suddenly dawned on me that I have been a complete idiot and have checked the wrong sensor. The sensor I was referring to above is sited inside the ecu box not the one in front of cylinder head . I will nip out and disconnect the correct one later to see if it has any effect. My icarsoft i930 reader does show cars coolant temperature and there is no eml illuminated which led me to believe all was well but Ill defo check it out just the same. .
... I did disconnect a temp sensor previously when Nodge suggested it could be a possibility. It didn't make difference unfortunately and rather than buy a new one I had worked on the assumption that the ecu would input a default reference which kind of ties in with comment above. However its now suddenly dawned on me that I have been a complete idiot and have checked the wrong sensor. The sensor I was referring to above is sited inside the ecu box not the one in front of cylinder head . I will nip out and disconnect the correct one later to see if it has any effect. My icarsoft i930 reader does show cars coolant temperature and there is no eml illuminated which led me to believe all was well but Ill defo check it out just the same. .
Ok I removed the MAF sensor and it didnt have any effect. I then removed the coolant temperature sensor and put everything back together. It started straight away.so I took it round the block. The red temp light is on as I expected it would but the fan is also on constant. Even after switching off engine it remained on for about 2 minutes. Is this what you would expect to happen ? Ill try to start it again a little later tonight to see if starting problem is resolved. It shouldn't normally start so if it does it will be very very promising. Dont want to get ahead of myself but assuming it does start tonight Would it be ok to use it for another day with fan running constant or do you think it may be in danger of burning motor out ?.
Nodge68
Well-Known Member
The fans are kicking in because the ECU can't tell how hot the engine is. It simply defaulted into safety mode. The fans should be able to cope with one day of running flat out. If you, like me has the heating control set at windscreen/floor all the time, then the fans run at slow speed constantly anyway.
The CTS is a last resort but can cause some running issues on occasion.
The CTS is a last resort but can cause some running issues on occasion.
Well now I am getting very hopeful as it started again no problem. The fan and engine management light is on as expected but I genuinely cannot get smile off my face . Ill fit a new sensor tomorrow and keep my fingers crossed. Ill let you know outcome thanks again for your help and advice
The fan and engine management light is on as expected but I genuinely cannot get smile off my face . Ill fit a new sensor tomorrow and keep my fingers crossed. Ill let you know outcome thanks again for your help and advice Hi all looking for one final push to get over the line as I'm not out of the woods yet. The new coolant sensor hasn't fixed the issue. The Situation is that if i disconnect the coolant sensor plug the car starts 1st turn of key every time. If I put plug back on it resorts to taking six or more attempts. There must be something in this circuit causing the issue.
The sensor only has two wires (blue/white and green/brown). I tested the voltage with key at on position and I get 5 volts from plug connector at blue/white wire side. I get zero from the green/brown side. If I test resistance between each side of the plug connectors I get a reading of 1.0.
If I take resistance reading from white/ blue side to earth I get 1.0.
If I take resistance reading from green/brown side to earth I get zero resistance 0.00. Can anyone decipher from these readings ???
The sensor only has two wires (blue/white and green/brown). I tested the voltage with key at on position and I get 5 volts from plug connector at blue/white wire side. I get zero from the green/brown side. If I test resistance between each side of the plug connectors I get a reading of 1.0.
If I take resistance reading from white/ blue side to earth I get 1.0.
If I take resistance reading from green/brown side to earth I get zero resistance 0.00. Can anyone decipher from these readings ???
Nodge68
Well-Known Member
The ECU will send +5 Volts down one wire and will calculate engine temperature by monitoring the Voltage returned on the other wire. There's nothing more to it than that really. Your starting issue is resolved if the ECU is defaulted to a hot engine by removing the CTS plug, but worsened on a warm engine. It's almost like the ECU is confused somehow, although that is unusual tbh.
It is a strange fault which might need T4 to resolve, at this point anyway.
It is a strange fault which might need T4 to resolve, at this point anyway.
Do you know if the other readings taken from the plug are what would be expected ? My suspicion is that there is a damaged wire in the loom. The plug loom goes into a plastic junction box a few inches below the sensor.It does look like it has been compressed at the entry point and I thought I could see tiny strands. See pics. I stripped back but once stripped i couldnt really see any obvious damage.. What do you reckon ? Its really difficult to see where these two wires head to next. as ideally would like to find both ends and test further.
Joe_H
Well-Known Member
I agree with Nodge. however, I thought you bought an Icarsoft reader ??? surely this can read CTS and monitor it ? Otherwise you need to back-probe the two wires to the ECU. The white blue is supply from the ecu (pin 28, the green brown is the signal to the ecu. Pin 32.
NEVER put a multi-meter on resistance range between a supply wire and ground !
You have 5v apparently, and you have a signal return to the ECU (otherwise if no signal return it would be in 'limp mode' all the time) So either you are losing the reference voltage or something is impeding the signal return.
Start off with the Icarsoft and see if the readings for cts are sensible. (you have a relative with the same type of car so you can check on his with the icarsoft to look at a normal range)
Then test the cable runs to the ECU. You can also test the 5V from the ecu to ground using a suitable automotive test light that places no more than 100 or 200 mA load via the bulb - it should light. (it is known it the automotive world as a 'scope on a rope' - NOTE - NOT a standard 12v bulb - a proper test light - which should be in every mechanics tool box. Taking reading with DMM's is often misleading due to the extremely high input impedance.
Surely this is one of the main reasons you bought the diagnostic kit ?
Joe
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Hi thanks again for input ! Yes I had checked coolant temp on my icarsoft previously and compared readings to brothers car.
Mine was showing 20.2 prior to starting compared to brothers 36.25. Once started at idle mine was reading 33 and his showing 32.
He sold his car at weekend so unable to revisit his. The fact it was registering similar readings was a smoke screen and led me to believe there was no issue with my sensor. I had also read that a failed sensor triggers a eml and fault code. Obviously given recent developments the plug ,wires or confused ecu on this circuit do hold the answer to my issue.
If you look at picture posted above you can see there appears to be something on the wire but it was too small to tell if it was fraying.Both wires were definitely creased where they entered the plastic junction box casing. My thinking is that any damage to these wires would affect the variable resistance figure going to the ecu. My plan is to check continuity from the sensor plug to the two ecu port numbers you have kindly identified for me. This of course is on the assumption they both go direct to ecu and zero resistance is expected. Do you know if this is correct ?
Mine was showing 20.2 prior to starting compared to brothers 36.25. Once started at idle mine was reading 33 and his showing 32.
He sold his car at weekend so unable to revisit his. The fact it was registering similar readings was a smoke screen and led me to believe there was no issue with my sensor. I had also read that a failed sensor triggers a eml and fault code. Obviously given recent developments the plug ,wires or confused ecu on this circuit do hold the answer to my issue.
If you look at picture posted above you can see there appears to be something on the wire but it was too small to tell if it was fraying.Both wires were definitely creased where they entered the plastic junction box casing. My thinking is that any damage to these wires would affect the variable resistance figure going to the ecu. My plan is to check continuity from the sensor plug to the two ecu port numbers you have kindly identified for me. This of course is on the assumption they both go direct to ecu and zero resistance is expected. Do you know if this is correct ?
Joe_H
Well-Known Member
According to the schematic on Rave - yes, the wiring is direct from the sensor to the ECU
I suggest you get a copy of Rave >2001 for your model
Thanks for this ! Yes I have copy of rave and was looking to find a diagram of this. All I could find however was this small paragraph ...
Engine Coolant Temperature (ECT) Sensor
The ECM monitors Engine Coolant Temperature (ECT) via the ECT sensor. The ECM
(C0914) provides a feed to the ECT sensor (C0169) on a KG wire. As ECT rises, the
resistance of the sensor falls. By measuring the voltage returned from the ECT sensor
(C0169) on a KB wire, the ECM (C0914) can determine ECT.
Did you manage to get those ecu wire port details from RAVE ? I clearly need to explore rave much further or perhaps I am just searching wrong section.
Engine Coolant Temperature (ECT) Sensor
The ECM monitors Engine Coolant Temperature (ECT) via the ECT sensor. The ECM
(C0914) provides a feed to the ECT sensor (C0169) on a KG wire. As ECT rises, the
resistance of the sensor falls. By measuring the voltage returned from the ECT sensor
(C0169) on a KB wire, the ECM (C0914) can determine ECT.
Did you manage to get those ecu wire port details from RAVE ? I clearly need to explore rave much further or perhaps I am just searching wrong section.
Joe_H
Well-Known Member
The circuit diagrams are accessible from the main page on rave where you normally open 'Workshop manuals' don't open that - simply look down the list for 'electrical library' - below that is 'electrical circuit diagrams' - ALSO let me correct the description I gave above with regards to operation and which 'wire colour does what! - the GREEN BROWN IS GROUND VIA THE ECU - on PIN 32 of connector CO606 of the ECU !!!!
BLUE WHITE is 'sense' on pin 28 of connector CO606 of the ECU -
PLEASE NOTE THE ABOVE !!!!!!.
I would first like you to check the info you have posted in the above post of yours ?
Where exactly in rave did you read that ? - and - is that for the TD4 as it differs in colour codes and description from my data - considerably. ! - also, are you sure you definitely got a TD4 sensor ? (No Worries as we can check - keep reading)
After looking at the data I have here. The system on the TD4 works like this -
Internal to the ECU is a potential divider, from the centre of the potential divider is a sensor wire (could also be considered a 'feed - but is not really that in the way we normally consider these things)
This is pin 28 on the centre connector block of the ecu (CO606) -(there are 5 connector blocks) and is 'slate and Blue' - effectively your white/blue
The Green Brown wire from pin 32 on the same ecu connector is a GROUND !.
What happens is this - the ecu provides - and reads - the voltage from it's internal potential divider.
In the EXTERNAL CTS, there is a negative temperature coefficient thermistor. (consider this a resistor) .
This is in parallel with the lower resistor in the potential divider inside the ECU
As the coolant temperature rises the resistance of the thermistor drops, as this is in parallel with the lower resistor in the potential divider, the voltage at the junction of the two resistors in the ECU potential divider changes. - hence the voltage sensed by the ecu changes.
SO, you should be getting 0 (zero) ohms from Green brown to ground with the multi-meter and - reading of 'X' volts at the Blue/white (slate) connector - X as as don't know the actual voltage from the potential divider. - (let us presume it is indeed 5 volts)
As the 'resistance' of the thermistor in the CTS decreases with rising temps. then the voltage X (let us presume 5V)) will drop as the temperature increases.
(let me know If you want the math)
So, according to the data - is you measure the green / brown terminal to body ground it should be 0.0 ohms.
Now, WITH THE MULTIMETER on VOLTAGE DC - If you measure the Blue / White to ground it should be - some sort of voltage - presume around 5 V. - this should be the same if you measure the voltage across the two terminal in the plug - blue white and green / brown.
Ok, let me know the results.
Now, put the multimeter back to OHMS range (K ohms here !), and measure the resistance in ohms between the two terminals of the CTS (with the plug disconnected - note - the CTS terminals only in this case - with the plug disconnected - NOT the plug - the CTS itself ! - let me know the result. (also the approximate temperature of the coolant which is going to be around ambient of not run for a considerable time - or - about 80 / 85 degrees C (edit - originally I put F- doh) or so if run recently (you will have to guess that bit) - should be between 1 and 4K ohms depending on coolant temp)
It is now obvious that this CTS does not operate as a lot of them do. In most cases a constant voltage is fed to a terminal on the CTS, the CTS is then grounded through the engine block. The other terminal senses a variable signal back to the ECU. THIS - on the TD4 is not how it works - it is different - ! (as described above - it operates by applying a parallel resistance to the R2 of the potential divider inside the ECU. - a failed lower resistor in the ECU (R" in the divider could account for the issue but we need to check other areas first.
Please do the above checks very carefully and again, let me know the results.
reminder - When checking the resistance across the CTS sensor with the plug disconnected - the meter should be on Kohm range. (unless of course your meter is auto ranging) - also make sure you are reading the correct RANGE on the multi meter. for example - not 1 ohm - but possibly 1K ohm - the meter will tell you.
Joe
BLUE WHITE is 'sense' on pin 28 of connector CO606 of the ECU -
PLEASE NOTE THE ABOVE !!!!!!.
I would first like you to check the info you have posted in the above post of yours ?
Where exactly in rave did you read that ? - and - is that for the TD4 as it differs in colour codes and description from my data - considerably. ! - also, are you sure you definitely got a TD4 sensor ? (No Worries as we can check - keep reading)
After looking at the data I have here. The system on the TD4 works like this -
Internal to the ECU is a potential divider, from the centre of the potential divider is a sensor wire (could also be considered a 'feed - but is not really that in the way we normally consider these things)
This is pin 28 on the centre connector block of the ecu (CO606) -(there are 5 connector blocks) and is 'slate and Blue' - effectively your white/blue
The Green Brown wire from pin 32 on the same ecu connector is a GROUND !.
What happens is this - the ecu provides - and reads - the voltage from it's internal potential divider.
In the EXTERNAL CTS, there is a negative temperature coefficient thermistor. (consider this a resistor) .
This is in parallel with the lower resistor in the potential divider inside the ECU
As the coolant temperature rises the resistance of the thermistor drops, as this is in parallel with the lower resistor in the potential divider, the voltage at the junction of the two resistors in the ECU potential divider changes. - hence the voltage sensed by the ecu changes.
SO, you should be getting 0 (zero) ohms from Green brown to ground with the multi-meter and - reading of 'X' volts at the Blue/white (slate) connector - X as as don't know the actual voltage from the potential divider. - (let us presume it is indeed 5 volts)
As the 'resistance' of the thermistor in the CTS decreases with rising temps. then the voltage X (let us presume 5V)) will drop as the temperature increases.
(let me know If you want the math)
So, according to the data - is you measure the green / brown terminal to body ground it should be 0.0 ohms.
Now, WITH THE MULTIMETER on VOLTAGE DC - If you measure the Blue / White to ground it should be - some sort of voltage - presume around 5 V. - this should be the same if you measure the voltage across the two terminal in the plug - blue white and green / brown.
Ok, let me know the results.
Now, put the multimeter back to OHMS range (K ohms here !), and measure the resistance in ohms between the two terminals of the CTS (with the plug disconnected - note - the CTS terminals only in this case - with the plug disconnected - NOT the plug - the CTS itself ! - let me know the result. (also the approximate temperature of the coolant which is going to be around ambient of not run for a considerable time - or - about 80 / 85 degrees C (edit - originally I put F- doh) or so if run recently (you will have to guess that bit) - should be between 1 and 4K ohms depending on coolant temp)
It is now obvious that this CTS does not operate as a lot of them do. In most cases a constant voltage is fed to a terminal on the CTS, the CTS is then grounded through the engine block. The other terminal senses a variable signal back to the ECU. THIS - on the TD4 is not how it works - it is different - ! (as described above - it operates by applying a parallel resistance to the R2 of the potential divider inside the ECU. - a failed lower resistor in the ECU (R" in the divider could account for the issue but we need to check other areas first.
Please do the above checks very carefully and again, let me know the results.
reminder - When checking the resistance across the CTS sensor with the plug disconnected - the meter should be on Kohm range. (unless of course your meter is auto ranging) - also make sure you are reading the correct RANGE on the multi meter. for example - not 1 ohm - but possibly 1K ohm - the meter will tell you.
Joe
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Joe_H
Well-Known Member
No worries mate, at least the problem sees to be isolated at the moment.
There is another measurement I want you to take please. With the ignition OFF please measure the resistance (ohms / Kohms) between the two terminals of the PLUG for the CTS unit - so with ignition off - and cts unplugged - measure the resistance between the two pins of the plug one with the green and brown and blue white wires connected to it. - this - in theory - should measure the resistance of the lower resistor (R2) of the potential divider inside the ecu.
There is another measurement I want you to take please. With the ignition OFF please measure the resistance (ohms / Kohms) between the two terminals of the PLUG for the CTS unit - so with ignition off - and cts unplugged - measure the resistance between the two pins of the plug one with the green and brown and blue white wires connected to it. - this - in theory - should measure the resistance of the lower resistor (R2) of the potential divider inside the ecu.
Skinny Mike
Well-Known Member
Hi mike, When nodge first mentioned the ecu possibly being confused I nipped out disconnected the negative lead and then removed the plugs from ecu for 20 minutes. It didnt resolve anything but looks like its also worth giving your method a try as well. Ill be able to get on to it after work tomorrow .cheers
Hi All, I have carried out the checks above and here are the results...
With the ignition OFF the resistance (ohms / Kohms) between the two terminals of the PLUG is 1.028
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
With ignition key on the voltage between two terminals of plug is 5.03v. I get same 5.03 between blue/white and ground.
Hope these readings make sense.
In addition to above I removed both battery terminals for 24 hours to see if that would reset ecu in case it was confused. I also got hold of replacement working loom just to help rule out damaged coolant wires. Both coolant wires on old loom turned out to be fine as showing zero resistance between plug and ecu . Replacement loom same readings.
What do you reckon based on above ?
With the ignition OFF the resistance (ohms / Kohms) between the two terminals of the PLUG is 1.028
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
With ignition key on the voltage between two terminals of plug is 5.03v. I get same 5.03 between blue/white and ground.
Hope these readings make sense.
In addition to above I removed both battery terminals for 24 hours to see if that would reset ecu in case it was confused. I also got hold of replacement working loom just to help rule out damaged coolant wires. Both coolant wires on old loom turned out to be fine as showing zero resistance between plug and ecu . Replacement loom same readings.
What do you reckon based on above ?
