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Mulptile thermostats replacement, P0128, and fan constantly running
I have a 2011 Mini Cooper S convertible with 79K miles. At some point I got a check engine light and a P 0128 code for low coolant temperature. The high-speed fan was also running constantly even for a significant amount of time after the car was off. You would expect the fan to run if the car was hot, but the maximum temperature achieved even with spirited driving was 67C.
Based on that diagnosis I replaced the coolant temperature sensor on the top the of the thermostat housing. That did not change anything and the P0128 code persisted, and the fan was continuously running. I then replaced the entire thermostat housing with an Mahle one. Nothing changed after the replacement, so I took it to a Mini mechanic.
The mechanic stated my thermostat was bad and replaced it with an OEM one they bought from the dealer. That also did not fix the issue. The mechanic then replaced the auxiliary coolant pump for the turbo in the hopes that would resolve the issue. It did not. The coolant temps are still at 67C or below and the fan constantly runs even after the car is off. The mechanic then used their Autologic tool to run diagnostics on all the CAN connected modules and found no issues. They then updated all the modules to the latest version. That still did not fix the issue or have any noticeable changes.
At this point we are both stumped as to what could be causing the problem. Clearly the car is not getting up to temperature in the prescribed amount of time so the P0128 code is accurate. At this point any help or suggestions would be more than welcome.
It looks like your "mechanic" is a parts changer not a troubleshooter.
Also, Mahle is the OEM supplier to MINI for the thermostat; the only difference between the Mahle stat and the dealer stat, is the MINI stamped into the side of it.
See the schematic below; you'll need to find someone with a lab scope that knows how to use it.
In the schematic, you'll notice MINI changed the cooling temp sensor circuit (arrows at the top) in 2012, you car (2011) is on the right side of the vertical red line. You'll notice there are four wires that go to the connector of your MAP controlled thermostat. The schematic indicates that pins 1 and 2 are a pulse-width modulated heater circuit that is used to open and close the thermostat; for example. During full throttle, the DME will send a signal to the thermostat to heat it up (opening the thermostat) providing additional cooling to the engine. The temperature sensor (pins 3 & 4) appears to be the temperature sensing circuit; it also appears to be a ground controlled circuit, meaning the DME switches the circuit on when you start the car. The reference voltage comes from Pin 14 of the DME; It's probable a 5 volt reference circuit.
Connect a lab scope (back probe) to pin 4 (yellow wire) on the back of the thermostat electrical connector, and monitor the voltage on the circuit. Start this test when the engine cold (stone cold), and record the voltage. Look for a change of state (voltage change) as you start the car and the engine warms up. Let us know what you find.
It looks like your "mechanic" is a parts changer not a troubleshooter.
Also, Mahle is the OEM supplier to MINI for the thermostat; the only difference between the Mahle stat and the dealer stat, is the MINI stamped into the side of it.
See the schematic below; you'll need to find someone with a lab scope that knows how to use it.
In the schematic, you'll notice MINI changed the cooling temp sensor circuit (arrows at the top) in 2012, you car (2011) is on the right side of the vertical red line. You'll notice there are four wires that go to the connector of your MAP controlled thermostat. The schematic indicates that pins 1 and 2 are a pulse-width modulated heater circuit that is used to open and close the thermostat; for example. During full throttle, the DME will send a signal to the thermostat to heat it up (opening the thermostat) providing additional cooling to the engine. The temperature sensor (pins 3 & 4) appears to be the temperature sensing circuit; it also appears to be a ground controlled circuit, meaning the DME switches the circuit on when you start the car. The reference voltage comes from Pin 14 of the DME; It's probable a 5 volt reference circuit.
Connect a lab scope (back probe) to pin 4 (yellow wire) on the back of the thermostat electrical connector, and monitor the voltage on the circuit. Start this test when the engine cold (stone cold), and record the voltage. Look for a change of state (voltage change) as you start the car and the engine warms up. Let us know what you find.
I have an r55, 2011 clubman with no turbo. Same issue. This happened to me about 2.5 years ago while living in Texas. I replaced the sensor - no change. However, since I didn't have my garage and was stationed down there for military duties, I elected to get the replacement done at the Dallas Mini dealership. They replaced the thermostat with a new factory one. Problem gone ... Until now.
I tried just the sensor first. O'Reilly's had the only one in stock, and it is aftermarket. Just like in Texas, the new sensor did nothing. I replaced the whole thermostat with an aftermarket from Amazon that had good reviews. I elected to use the sensor I got from O'Reilly's rather than the one that came with the thermostat (for now).
No luck. I reset the codes many times with my personal code scanner. Whether engine is running or just key in "on" position, resetting the codes won't clear that one. I took it to a local mechanic i trust, and they supposedly cleared it with their fancy $5000 snap on computer. I drive around for a bit, and the code is still there, "permanent".
Where my mini is not the turbo, should I follow these same steps? What can I do if I don't own a lab scope? Will a volt meter suffice?
Note - when I have the car "on" but engine not running, and i reset the code then, even though the code stays, the fan will stop. The car heats up to normal temps. In fact, usually, the fan won't come on for the rest of the day, and the car runs normal. Usually, the next morning the fan comes on steady again though, before the car even has time to warm up.
Simply put, the two wires that goes to the ETS(engine temperature sensor) located on top of the thermostat is not making contact. Take the two wires off the plug and plug them directly to the ETS terminal and watch the fan shut off when turning the car off. I’ve had the same exact problem what you have and it works beautifully.
note: the two wires are polarity but don’t worry, it won’t hurt the DME if wires installed the wrong way, simply flip it around. Also use a heatsink on one of the wires so they don’t touch each other.
Simply put, the two wires that goes to the ETS(engine temperature sensor) located on top of the thermostat is not making contact. Take the two wires off the plug and plug them directly to the ETS terminal and watch the fan shut off when turning the car off. I’ve had the same exact problem what you have and it works beautifully.
note: the two wires are polarity but don’t worry, it won’t hurt the DME if wires installed the wrong way, simply flip it around. Also use a heatsink on one of the wires so they don’t touch each other.
I kindly thank you for your response. I do have a follow on question - if this is the case, how come I get a steady reported temperature to my OBD scanner while monitoring live data? The fluid heats up exactly as one would expect it to, all the way up to the 200-215F range. I'm not unwilling to try, because that connector is cheap and easy to replace. I just don't understand why that would change or improve anything if it's currently getting a good temp reading anyways. The connectors and wires all look like they're in very good condition.
That ETS sensor on top of the thermostat does run the fan. I had this same issue for quite some time and now my issues with the fan has been "SOLVED" and fixed.
I have an r55, 2011 clubman with no turbo. Same issue. This happened to me about 2.5 years ago while living in Texas. I replaced the sensor - no change. However, since I didn't have my garage and was stationed down there for military duties, I elected to get the replacement done at the Dallas Mini dealership. They replaced the thermostat with a new factory one. Problem gone ... Until now.
I tried just the sensor first. O'Reilly's had the only one in stock, and it is aftermarket. Just like in Texas, the new sensor did nothing. I replaced the whole thermostat with an aftermarket from Amazon that had good reviews. I elected to use the sensor I got from O'Reilly's rather than the one that came with the thermostat (for now).
No luck. I reset the codes many times with my personal code scanner. Whether engine is running or just key in "on" position, resetting the codes won't clear that one. I took it to a local mechanic i trust, and they supposedly cleared it with their fancy $5000 snap on computer. I drive around for a bit, and the code is still there, "permanent".
Where my mini is not the turbo, should I follow these same steps? What can I do if I don't own a lab scope? Will a volt meter suffice?
Note - when I have the car "on" but engine not running, and i reset the code then, even though the code stays, the fan will stop. The car heats up to normal temps. In fact, usually, the fan won't come on for the rest of the day, and the car runs normal. Usually, the next morning the fan comes on steady again though, before the car even has time to warm up.
Yes you can use a multi-meter, but if you have a scan tool with "live data" you can pull up "ECT" (engine coolant temp) under the DME heading. In my experience the MAP controlled portion of the thermostat fails much more frequently than the temperature sensor.
My sons mini had some coolant leaking issues so we replaced the Thermostat. After that, there were still some issues that culminated in overheating. We have rebuilt the cylinder head (include fly cut and valve seat grinding so that looked like new.
replaced timing chain and guides.
replaced all gaskets and seals
added metal coolant cross tube.
new water pump and pulley
new belt
Did not replace the thermostat that was on the engine when it overheated.
All back together ok and runs well, but has code 2947 coolant temperature sensor, signal: Permanently stuck at low.
If I look at the signals with my scanner, I can see 2 temperature values:
Coolant Temperature (I assume from the sensor on top of the thermostat housing)
Engine Control Temperature (I assume is from the lower connector of the Thermostat housing)
-This may be derived from something else. The coolant temp rises as expected as the engine runs. The Fan is running all the time so not sure if it reaches full temperature or not. The Engine control Temperature does rise and change a bit but seems to stay around 100 Deg F.
Data recorded by XTOOL D9SPro
I have not been able to find information about this data to determine a course of action.
No other codes of interest.
What is the expected relationship between these two measurements?
Do I just order another Thermostat and get on with life?
The engine coolant temperature (ECT) sensor is reporting a ridiculously high coolant temperature (353F). Did you thoroughly bleed all air from the cooling system?
Otherwise, replace the thermostat assembly and then go from there.
And the two electrical connectors on the thermostat assembly are for the ECT sensor (top) and MAP thermostat (bottom).
Last edited by Maybe, maybe not; Today at 08:50 AM.
There is a units display issue here. I believe both are shown a Fahrenheit values even though it says degrees C...
I used a vacuum bleeder to load the coolant and I'm not seeing any issues and the temperature when running also feels "cool" is anything.
I'd like to understand if the chart shows anything useful with the traces. I have another thermostat on order :(.
The scan tool is possibly reporting temperatures in Celsius because the commanded MAP thermostat temperature could make sense (104C/220F).
In contrast, the 177C/353F is crazy high for coolant temperature, fitting with the idea of a bad ECT sensor and the observed constantly running radiator fan.
Here's a new test drive. I reset the codes and went for a drive. There were no codes after this short drive and the curves look the same. Still running a bit cold. Ambient temp is 82 F.
How many total minutes was the test drive? Is the captured live data at the end of the drive?
Does the radiator fan still run continuously or does it now operate as expected?
I wonder if you will get higher coolant temperatures when the fault code reappears. If not, one possibility is that there are two separate problems: (1) a stuck open thermostat and (2) a bad ECT sensor.
I don't know what the engine control temperature measures. I had earlier assumed that it was the target coolant temperature set by the DME via the MAP thermostat but that doesn't make sense with the low 115F reading. Does your scan tool describe the engine control temperature?
Total time was about 29 minutes. So I would expect a bit higher temp.
Next Steps: Check for air in system again. Heater, bleeder at Thermostat...
Replace thermostat when the new one arrives.
03-02-2022, 04:52 PM
