How Coolant Temperature Sensors Work :: EFI Explained by Matt @ M-Tech Automotive

How Coolant Temperature Sensors Work :: EFI Explained by Matt @ M-Tech Automotive


I’m Matt from mtech and in this video of the F I explained we’re going to talk about these the coolant temperature sensor what we’re going to cover is what they are how they work what relevance they have to EFI how to test them what to watch out for when using them and some further in-depth technical electronic fuel injection formation regarding these actual sensors so first of all what are they well this is a Bosch 2 pin type mini timer type engine coolant temperature sensor and this is the sensitive be used in conjunction of the engine management system not the dashboard gauges example because they usually have one wire connection on them and they air through the chassis at the sensor whereas this one actually goes through two pins on top of the sensor standard mini timer type two pin connector and the other types of sensors for example this forward one has a style of character like what we would call a dead so type connector and wouldn’t be compatible with any intervention it uses these type of sensors and that is because of the way they work now these sensors are a negative temperature coefficient sensor which means it’s resistance decreases as the temperature increases and each type of these sensors has their own particular calibration curve and if we go ahead and draw a curve one of these sensors they look something like this given a temperature which increases and resistance in ohms which increases that way the resistance Falls other temperature increases and this curve is specified for each type of sensor though these Bosch sensors and indeed the Bosch air temp sensors all follow a similar sort of curve and so most general range margins and after market management systems all come normally set up for these Bosch sensors of course you can calibrate in these curves into into your international systems or any interventions that we’re going to be tuning with so one means a nose as well as the curve is not a straight line curve it’s a logarithmic curve which means the sensitivity is reduced as the temperature increases and that’s something we’ll talk about later on when we discussed the further technical information about these sensors so what is the use of these sensors with relationship electronic fuel injection well the first thing is back in the day of carburetors most people would have to pull out a choke whence first up in the car and the reason for that is the way engine is cold the petrol doesn’t atomized very well so what you need is in a bit more fuel in there to get a good combustion we get a good burn from the engine itself so the ECU of the enzymatic system is looking at the temperature reported by this sensor and if the engine is cold it’s going to put in slightly more fuel a multiplier of the fuel table so I some additional fuel and it’s also used during cranking and starting so that the engine note the engine running system knows engine is cold when cranking or it’s hot when cranking so again you can put in the right amount of fuel to get the engine running properly now the throughout the 90s and the early 2000s these sensors were usually independent for the engine management system the dashboard gauges and the cooling fans would usually have additional sensors to control those different areas of the cars but lately more modern systems what they tend to do is just having one sensor in the cooling system and that would then send off signals for the ECU to trigger the cooling fan and also perhaps over CANbus indicate that the driver the temperature of the engine on the dashboard and again there’s some things for account for when wiring these into cars which will go through shortly so how to test these senses well being a thermistor and a simply resistor we can measure its resistance across these two pins checking against the calibration curve or the datasheet for the sensor to make sure it’s read correctly and we do a short video on that and how to test them which one need to below so what to watch out for in terms of using engine management systems and these sensors well as I’ve previously said every sensor has a different type of curve depending on their part number although Bosch type sensors are usually very similar forward sensors again completely different as are most Japanese sensors so when using an energy management system or changing a coolant temperature sensor is important to get the one that’s matched for the issue you’re using or usually see which has a programmable table such as our systems or knotek or Android or emits or any of these higher level systems which we have to calibrate in the curve of these sensors so what’s our watch out for with these sensors well if you’re looking at fitting aftermarket management to a more modern car it’s probably going to using this sensor to drive the dashboard you might be driving the dashboard directly more than likely driving it through the original factory ECU on the car trying to a turn out to CANbus and then staying back to the driver so it’s always good to assume that you could tap into this sensor line for your ECU well that’s not going to be possible and the reason for this is on how the upper two ECU system uses these sensors to monitor the engine coolant temperature the way it works is you have the ECU and what the ECU does is it outputs a voltage which goes through the thermistor or the coolant sensor which looks like that to ground now sometimes that ground will come back to the ECU for a sensory ground or sometimes that will just go to a common ground on the car but the problem is if you t piece into this with your aftermarket engine management system so I put aftermarket ECU and you come in like this for your coolant sensor line what happens is the resistance within this system here can affect the reading of the coolant temperature sensor and not only that more modern easy use due to the way the curve is logarithmic well sometimes switching an extra bias resistor to get more accurate readings as the engine temperature increases again most engines since when support that so it’s very important if you want to retains time – program fitting into mountain systems you even feel you have a dashboard had an independent coolant temperature sensor or you fit another engine coolant temperature sensor specifically for your ECU another thing to note as well is if removing a factory ECU and fitting one of these coolant sensors the cooling fan may have been driven by the original ECU in which case you will need to install relay and user programmable output only all aftermarket management to drive a fan at specified temperature otherwise entry could overheat and it might not be something that shows up immediately under testing so it’s something to watch like so let’s go through how these coolant temperature sensors are used with an ECU in terms of mapping we’ve already said how in a traditional car with a carburetor you would use a manual choke we’ll try to enrich the mixture and therefore let the engine run better so let’s go through exactly what these do in terms of a modern link to you or an aftermarket ECU and the various tables that they’re used within within these ECU’s so the first table would be the warm-up enrichment table and this table typically looks like this okay what we can see here is this is a temperature that this sensor is reporting degree centigrade and this is the enrichment percentage of fueling so look up it’s basically willing from the main table which might say five milliseconds or seven milliseconds and they would check this table to see how much enrichment it wants to add some fuel depending on this temperature sensor so the curve might typically look like this and as you can see when the engine reaches its normal temperature around ninety degree centigrade it then puts in a hundred percent of the normal fuel so that’s just what we feel like you’re saying if no other correction applied related to this engine management sensor also another setting that we they’ll be a scalar setting would be the temperature which the fan should come on and which have had to turn off and there be another factor for this sensor which would be the starting and cranking which again would look similar to this but might relate to a pulse width to apply when cranking the engine below a certain rpm as to how much to inject to get the engine start properly there also in the end after starting enrichment which would be a very short time of enriched fuel again raising to this coolant temperature sensor and for example in a hot start a condition like 15 G off and then momentarily back on very unlikely the sensor will cause much difference to the engine so it’s a third-tier sensor lot of priority sensor it’s more of a help the engine run properly sensor one thing to note is that this is a coolant temperature sensor because it has the enclosed sensor element inside of there if we compare it to an air temperature sensor you can see how the element is exposed and this is because the coolant temperature sensor doesn’t need to react very fast to changing changing statuses because the coolant itself takes a while to change in temperature where is the air temperature can fluctuate quite rapidly especially on turbocharged cars and so the elements of the thermistor is actually exposed so that it can have a faster reaction time and that’s all for this video on coolant temperature sensors to check out more sensors and more videos and more technical guides and what else we plan on covering Tech Zone be sure to subscribe with the link below and we’ll see you next time you


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