Mini Cooper ECT issue
Found this Mini with a no start on cold start but can get it to start eventually when playing with the throttle. Once it starts it runs rough and you have to keep the idle high. Once the engine warms up it runs fine. As of now there is no codes. Found when the engine is cold (sitting over night) the ECT temp data pid reads at 165 degrees F. The thermostat housing has been replaced twice by another shop which includes a new ect sensor. With the ect unplugged I am only getting 3.3 volts coming from the computer. Getting the same voltage at the computer connector. Looked up info on the sensor and found the computer should be sending out 5 volts. The engine computer has also been updated by the other shop. Would there be any other reason the computer would only be sending out 3.3 volts other then a faulty computer?
It's possible the ECT signal wire has a resistive short to ground, pulling the signal voltage down partially. Find the ECT signal wire at the engine computer and cut it in an easily repairable location. Now check voltage on the computer side. If it's now 5V, there's a wiring problem.
Something else on the 5V ref circuit is bringing the voltage down. You will need to refer to an OE wiring diagram and find out what is shared on that circuit.
I like Tyler's approach, i might add checking PCM powers and grounds if other 5v ref circuits are showing the 3.3v also.
I forgot to note that the other 5 volt ref circuits all read 5 volts. Also there are no codes which is strange.
Some of these MINI Coopers have gone through a few updates of the ECT. Since the thermostat assembly has been replaced, then it should have the latest ECT arrangement, but there is also an adapter wire harness for the updated design which I have seen people install incorrectly. So, make sure the old ECT sensor that is located in one of the coolant hoses near the thermostat (if this car still…
3.3V is normal. French engine right? They also are 3.3V at the sensor unplugged. Not relating to starting problems, but the colour of the CTS is also important. Overheating problems with fans not coming in, CTS not exactly matched with software. In my examples, only dealer CTS successfully brought the fans in at the correct temp.
Before cutting the wire at the computer , put a lab scope on the circuit in case the voltmeter is averaging out the voltage, that way you can rule out wires from injector or ignition interference , some times temperature can expand and separate things. just a thought
If it has direct injection the high pressure pump is defective,fuel pressure on cold start will be about 170 then build to 1200 when warm
I actually own 2 R56 Mini Coopers. First….there are 2 types of thermostat housings. One is kind of a internal set up and requires a special harness to mate to an earlier vehicle harness. The standard thermostat housing has a replaceable coolant sensor. Even the name brand replacement plastic thermostat housings have complete crap Chinese coolant sensors…they puke out or don't work at all. All…
I cut the ect wire at the computer and still found the 3.3 volts coming out of the computer. Double checked the other circuits and all tested good and with all other sensors with a 5 volt ref. unplugged the same voltage was found. Removed the new temp sensor and performed a resistance test and compared to spec. Found the sensor reading way out of spec. Replaced the temp sensor and now it's…
Nice. I wonder if there is a resistor or 2 in the ECT circuit and the 3.3v i a bias voltage 🤔
You are correct Brandon. I have seen some ambient temp sensors with the same. I can't remember which ones though.
even Though the problem is fixed I ld like to add. If the sensor was reading 165 warm and 3.3 on the signal wire then unplugging it what did the scanner show. I assume it would be whatever open ckt voltage would be which for the most part is -40. so if you had something else pulling the ckt low with the sensor unplugged it would only affect that signal ckt . You can have another reference ckt…