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at what temperature , 3.3volts off top of my head will be around degrees 12c the hotter the car gets lower the voltage at sensor colder volts will max out around 5volts, the sensor has one signal/feed and the other wire to it its a switched earth from the ecu. the other wires to thermostat are also direct back to ecu but these run on a 12volt rail and once again is switched earth through the ecu, the ecu is a MEV 17.4 this allows piloted thermostat ie the ecu can open and close it when it wants to,, never bother sticking the cheap thermostat housing on them there is a updated one cost around £120 and honesty a must do job for anyone the older type as just rubbish the plastic cracks then dont open and close at correct times cause all kinds of problems , if your having over heating issues this is one area the other is the water pump and coating come away or jockey wheel,
if put a temp sensor on its plug and lightly use a heat gun on end of it see if the voltage changes ie should drop to 0.1v of a volt when at 268c ie its limit
 

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Discussion Starter · #3 ·
Yes it's when I first turn car on. It's 3.3 so I was thinking it may be the ecm. So I did do a thermostat when we first got the car. My fan doesn't run unless I unplug the coolant temp sensor.
 

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Yes it's when I first turn car on. It's 3.3 so I was thinking it may be the ecm. So I did do a thermostat when we first got the car. My fan doesn't run unless I unplug the coolant temp sensor.
that sounds right at 20c ish 3.3volts is correct, and will reduce as car warms up,
there is a recent thermostat housing update part with piece of wiring due to oil getting to hot engine getting t hot and plastic housing cracking with heat below link shows what, it cures so many issues they all get with time, must be genuine part cheap Chinese ones are rubbish more harm than good,
 

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i have lost count the amount of problems that were fixed by just using a genuine housing and sensor
 

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Ok thanks for the info I will try a genuine thermostat housing
i would those engines are touchy at best of times, they also eat 02 sensors and genuine bosch ones is only way forward with them that said stretched timing chain tends to be why they fail and also oil burning due to valve stem seals on exhaust valves mainly
 

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car running pull the temp sensor plug off the temp sensor, within 5 seconds the fan should cut in,, if does not then you have a problem with fan circuit, ie fan, or wiring, or fuse gone or relay, or fan speed controller ie resistor pack,
i would next send a voltage with a probe tool to fan ee if it turns, of does then not fan at fault.
most common is fan as is resistor
 

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3.3volts is correct at sensor the hotter the car gets lower the voltage ie the sensor with heat increases resistance ie restricts the voltage back to ecu, if you put a jumper cable across the two pins on temp sensor this will throw fan on and eml and code for short to positive fault code, i do this to test the circuit from sensor to ecu, also check the earth return wire is in fact earthed with multi meter,
also diagnostics on live data you can watch coolant temp increase and rev car for a good 40 minutes at 3000 revs to induce loads of heat to the system while watching temp on live data , or probe the temp sensor on signal wire and watch the voltage at set times or recorded heat via diagnostics live data, its only way to begin to understand the system, also can monitor the piloted thermostat housing below it ie has a 12v feed to it, if this was faulty and not closing the engine would not get hot enough to throw fan on and effect everything else, the top rad hose is the feed from the thermostat pipe so the heat is forced downwards have seen people fit pipes the wrong way around and get in to all kinds of issue where it air bubbles at temp sensor and sensor only reads the hot air lock and not the coolant, this dont end well for many with engine damage if driven on like it, to check as car from cold warms up the top house should get hot first and bottom last, around 90c should start opening to move water through fully open around 105c on new housings and good knows what on cheap housing
 
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