temp sender circuit high

[cooper12000]

hi all I have a 57 plate ford focus 1.6 with the dreaded vvt engine. the original fault was the temp gauge didn't move and engine fan was running continually and heater didn't work was tepid at best.  I had the thermostat changed (***** expensive for a thermostat) and still have the engine fan running with no temp gauge.  however the heater works well so the thermostat was definitely  part of the issue.

I have had someone plug in their reader as the eml is on and it said coolant temp sensor circuit high.  when I asked them to elaborate what that ment they clearly didn't know and after much prodding said of its over voltage it should be 5v but its more than that so its out of parameter.  (what a load of rubbish)

 

my question is the coolant sensor defiantly part of the thermostat housing etc and what would cause this fault 

 

many thanks coop

[JW1982]

Temp Sender Circuit high means that there is an open circuit. This can either be caused by a defective temperature sender or a wiring defect.

Personally I would start with measuring the resistance of the temperature sender. The resistance of the temperature sensor is related to the temperature. The condition of the temperature sensor can be determined based on the temperature and the resistance value.

As far as I know the temperature sensor of the 1.6 TI-VCT is not integrated into the thermostat housing. The electric connector on the thermostat housing is for the (expensive) electronic thermostat.

[cooper12000]

where is the sender located if it isn't part of the housing

many thanks

coop

[JW1982]

The temperature sensor is located in in the coolant outlet cover below the ignition coil.

 

 

 

 

Depending on the production date op the car the cover can be made of aluminium with a threaded temperature sensor or made of plastic with a cylindrical shaped temperature sensor which is held in place by a metal retaining clip.

[isetta]

correct me if I am wrong. The temp sensor is a resistor that varies it's resistance with heat. cold = high resistance, hot = low resistance. If you take the connector plug off and bridge the two terminals in the plug on the end of the wire then the temp guage should go right up. if it does then you know it is faulty sensor (or poor connector terminals).

This is based on my knowledge of working on cars many many years ago. I assume the principle has not changed.   Hope someone points it out if I am wrong.

[JW1982]

Disconnecting and bridging the connector will only generate a DTC code because the resistance value is out of range. To make this work you have to bridge the connector using a resisitor of the correct value to simulate a certain temperature.

As far as I remember the resistor value must be 2800 ohm to read approximately 90 degrees Celsius.

[cooper12000]

2 hours ago, isetta said:

correct me if I am wrong. The temp sensor is a resistor that varies it's resistance with heat. cold = high resistance, hot = low resistance. If you take the connector plug off and bridge the two terminals in the plug on the end of the wire then the temp guage should go right up. if it does then you know it is faulty sensor (or poor connector terminals).

This is based on my knowledge of working on cars many many years ago. I assume the principle has not changed.   Hope someone points it out if I am wrong.

I do this a lot on my p6 sure fire way of checking if the gauge is knackered albeit fuel or temp etc short the sender wire to earth and the gauge goes full scale (or in my case it doesn't but when you short the other end to earth it does... meaning you have to trace through miles of bad rewiring but that's another story)  But as jw1982 says with modern cars it wouldn't work as anything out of range gets ignored by the ecu and generates a fault code causing the plane to crash (airbus 330) one of the reasons I much prefer older cars

thanks for all the replies it has given me something to check out which makes a lot more sense than what I was told this morning

coop

[JW1982]

Also be aware that the temperature gauge of the Focus MK2/MK2.5 is completely controlled by the PCM. The temperature gauge displays a calculated value and not the realtime value. The PCM uses data of several sensors to calculate the temperature. Every single one of these sensors can affect the temperature that is shown on the gauge. I have seen before that a defective sensor that is not directly related to the engine temperature caused incorrect temperature gauge readings.

On an engine with an electronic thermostat like the 1.6 TI-VCT a defective temperature sensor can be a cause of engine damage. If the resistance of the temperature sensor is way higher than it should be at a certain temperature but still within its resistance range the PCM "thinks" that the engine is still cold while in fact the engine already reached its normal operating temperature. Because the PCM "thinks" the engine is still cold the thermostat will not be opened which causes the engine to run hot. 

This is quite a bad design in my opinion. This is probably also the reason why Ford changed over to a normal mechanical thermostat on the later versions of the 1.6 TI-VCT.

[cooper12000]

hi all,  got round to doing the sensor today as I have been working nights seems to of fixed all the issues thanks so much for all your help

Coop

[Botus]

my understanding is the electric stat connected into the engine management systems,  can open rapidly if you accelerate hard / or uphill etc.  its was emission driven and allegedly benefits fuel consumption.  when it dies the fan runs frequently and you get  P0599 thermostat control circuit high    or similar P0597 circuit open, P0598 circuit low

 

[cooper12000]

17 hours ago, Botus said:

my understanding is the electric stat connected into the engine management systems,  can open rapidly if you accelerate hard / or uphill etc.  its was emission driven and allegedly benefits fuel consumption.  when it dies the fan runs frequently and you get  P0599 thermostat control circuit high    or similar P0597 circuit open, P0598 circuit low

 

the thermostat was replaced at great expense but the symptoms continued and the code I had was temp sender high circuit an electronically speaking ambiguous statement.  Turns out there was a broken wire at the plug and when tested the temp sender was fine so a more accurate statement would of been temp sender open circuit. 

 

[Botus]

my one was much happier after the new stat went in, cooling system back to normal fan operation returned to std... 

a year later much happier with a new coil pack, no sign of missing or codes, till a puddle built up in cam area (from the washer jet joke design directly above it).... but when coil pack changed the whole car drove differently to how it had been for the at least the last 3 years (I actually wonder if it had been swapped out years before for the wrong unit before we got it - there are 3 to pick from dependant upon chassis / engine code)