Automotive Technology Course | ECT IAT or Engine Coolant Temp. Sensor Testing

Automotive Technology Course | ECT IAT or Engine Coolant Temp. Sensor Testing


you you you the ECT sensor as seen on screen is composed of the sensor buddy thermistor and the to wire connector on the side the ECT sensor is a thermistor device with a negative temperature coefficient this means that as temperature goes up resistance and voltage output go down and vice-versa a high voltage value equals a low temperature on a low voltage value equals a high temperature the ECT sensor has the two terminals labeled ECT ground and reference voltage wire engine coolant temperature sensors operate with a five volt reference signal it is precisely the function of the ECT sensor to modify our changed as 5 volts reference according to the engine temperature the other light four terminal on the ECT sensor is the ground line this wire is often called sensor ground and it is shared by all the other sensors the five Philips reference line is always connected in series with an internal ECM resistor this forms the voltage divider network needed for the ECT sensor to function properly in the event that there is an ECT faulty code and the five Philips references present but no change can be seen that the scan tool suspect of faulty internal resistor in this case you would have to replace the entire ECM unit the IAT sensor or intake air temperature sensor is a close cousin of the ECD sensor the IAT sensor is also tested at exactly the same way just remember that the IAT sensor measures only air temperature and not that of the engine coolant the ECT sensor is basically tested by testing it’s two wires the ECD ground and the 5 volt reference wire both of these terminals the ground and the 5 volts reference signal wire are provided by the ECM the 5 volts references provided through an internal ECM resistor which sometimes tends to go bad remember the job of the ECT sensor is to bring this 5 volts reference closer or further away from ground depending on the coolant temperature the first step in testing the ECD is spaghetti baseline reading using the scanner this step will allow you to make comparisons later on after repairs have been completed step number two is to prove the ECT wiring using the scanner by disconnecting the ECT sensor connector and watching its signal voltage on the scan tool a value close to 5 volts reference should be seen this is the open-ended ECT voltage and can only be seen with the ECT sensor disconnected this open voltage also signals a low engine temperature then with the ECT sensor still disconnected jump the two ECT terminals when the ECT connector is jumped the scan tool should show a very low voltage signal or close to ground this also corresponds to a very high engine temperature which again corresponds to the negative temperature coefficient nature of the ECT sensor remember as temperature goes up voltage goes down and vice-versa first with the ICT sentencer disconnected the scanner shows low limit or low temperature limit this also corresponds to a high ECD voltage output level not all scan tools will show the actual voltage output from the ECT with the ECT disconnected the ECM is simply indicating that the signal is at its highest possible voltage level and lowest temperature indicating a very cold engine this says that the relationship between voltage and temperature is inversely proportional with the ECT connector jumped the scanner should show a high limit or lowest CD voltage this indicates that the lower the voltage the higher or hotter the engine will run in our case the high limit indicates a low voltage setting which should be very close to ground the C CT scanner testing procedure will never do away with the actual manual testing needed it is simply a preliminary way to test the ECT sensor using a scanner in the event that the scanner value doesn’t change while jumping the ECT connector it is a good indication that there are impending wiring problems also remember that it may be necessary to turn the engine on for the scanner to function and for this test to be viable a final point on testing the ECT sensor is to use the graphing feature of the scanner by glancing at the ECD voltage and taking the vehicle for a road test any impending wiring problems may show up on the ECD graph the glitch that we are looking for will definitely show up on the scanner screen watch as we jump and disconnect the ECT connector while watching the ECD graph this is exactly what you would see if you were Road testing the vehicle not all scan tools have the graphing capability but if it does use it it may save you a lot of diagnostic time step number three is to prove the ECT circuit using a digital multimeter start by crimping the red multimeter lead to the a CD ground wire and then connect the black multimeter lead to the battery ground in actuality you are doing a voltage drop across sensor ground and battery ground a normal reading of 100 millivolts for lowers desirable regardless of engine speed remember that the 100 millivolts rule can also be used to prove an test any other computer-controlled ground circuit double-check the ECT ground by swapping the digital black multimeter lead to battery voltage at this point in time you should see battery voltage at the multimeter screen step number four is to prove the 5volts reference circuit remove and change the black multimeter lead to battery ground then change the red multimeter lead to the AC T sensor signal or reference wire at this point in time you should see exactly what the ECT sensor is signaling the ECM remember you can only see the 5 volts reference with the AC t connector disconnected it is precisely the job of the ECT sensor to bring this 5 volts reference value further or closer to ground depending on engine temperature also with the multimeter nect sensor connected to a performance test by raising the engine speed and verifying a signal change at the multimeter screen by having into the ECT signal wire and disconnecting the ECT connector you are simply proving the five Philips reference line this 5 volts reference is provided and regulated by the ECM and it is the one that is shifted closer or further from ground by the ECT sensor itself as temperature changes the intake air temperature sensor or IAT is tested in exactly the same manner as the ECD sensor just remember to look for anything that affects the air temperature or air passage through the throttle body or intake manifold a cloud catalytic converter will make the exhaust gases backed up into the intake manifold which will raise the IAT censors value however this technique to test for a cloud converter only works if the IAT sensor is located right at the intake manifold and not the air duct you you


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