P0128 Code after replacing thermostat?
 

Hi everyone,

I'm at my wits end with my car. It's bitter sweet to drive it because I love it so much but if it's not one thing it's another so I need a little help.

I drive a manual 2009 Clubman S and recently the thermostat housing cracked open.

I managed to replace it myself with the wonderful guide I found here that linked back to the YouTube video of how to do the repair.

Long story short it's been three months since then. My car had been serviced and everything has been fine until it threw a CEL yesterday and when I checked the code was P1028. After searching the forums it seems like every post suggested that the thermostat needs to be replaced but it's brand new!

Any suggestions would be so helpful.

Thanks.

Check the wiring at the sensor and make sure both sensors wires are clipped back in and did not pop out due to a busted clips ( it happens ) . Also make sure you did not cut or chaff one of the wires on the wire bundle near the passenger side of the engine then it finally grounded out or something. Have not seen it happen much but a new one could have went bad again. If you got it at a dealership the thermo comes with a 2 year unlimited miles at most.

What thermostat did you use? According to Engine-Codes, possible causes are:

- Leaking or stuck open thermostat
- Low engine coolant level
- Insufficient warm up time
- Faulty engine coolant temperature sensor
- Engine coolant temperature sensor harness is open or shorted
- Engine coolant temperature sensor circuit poor electrical connection

OBD-II gives some good information too here, with some suggested solutions. I'd check out all of the above and see if it may help resolve your issue.

Thank you I'm going to dig back in there right now and check all the wiring. Ill let you know how it goes.

The connection at the sensor on the thermostat housing (lower back sensor) did not look disconnected at all but when I tugged on it it came right off as though it wasn't pushed in all the way. It appears the clip has been loosened enough it doesn't want to stay clipped. I pushed on it to no avail so I finally just reached down there and pushed the clip on the underside closed.

No idea if this will make any difference as it really did look like it was pushed in all the way but we will see soon if the CEL comes back on.

Yes, you are welcome. We have had a couple people break the tab on the plug socket and then it wiggles loose and throw a code.

Let me know after you do that and clear the code , if it comes back up again. :thumbsup:

Well I almost made it through my commute without the CEL coming back on but it did.

It was much farther then before though! My commute is 60 miles round trip and it came on almost at the end of that so I'm hoping that the clip just came loose again. I'm going to open it all back up again tonight and see how long it takes tomorrow.

Any other suggestions?

Well I got back in there today and all of the plugs were secure...

Does this mean I need to replace the Thermostat Housing again or are there any other things I can check before we go that route?

You could also make sure the pins are in full contact with the thermostat. Wiggle the plug while its running and see if you see a code. Its could just be loose enough on and off. Check the contacts. If still no good then the thermostat will need replaced.

Is it safe to do that with all of the air intake stuff removed?

You will have to try to reach it by the wire , don't remove the top portion or box of the intake, the lower tube ( that goes up by the headlight ) should be ok to remove just for this.

Alright I wiggled the plugs and unfortunately no code was thrown, is this confirmation that the thermostat housing needs to be replaced again?

Last time I purchased it from a seller on eBay so there was no warranty, is there a website that offers a warranty on these purchases? I'm baffled it has only been 3 months since I replaced it.

Was it a genuine MINI part from Ebay ? New or used?

Sounds like a bad part.

We have it here and if you have any issues the future, we are here. :)

Thank you for your support. I hadn't realized that the part I purchased was not genuine mini. That's a bummer but I'm sure the genuine part will last longer then 3 months!

I made an unfortunately confusing discovery today that I really need clarification on.

Everything went smoothly with the installation and she's running like new again BUT.

When I was working with the upper sensor on the thermostat housing I realized that the plug that goes into it is green plugging into the brown plug on the thermostat. This is exactly how it has always been I have been very careful not to mix these up. On the same bundle of plugs there is another that is brown that has been plugging into the top part of the air intake system.

Now in the video for this repair ( <a href="https://www.youtube.com/watch?v=ek4YJUvZTPc">Replace R55/R56 MINI Thermostat Housing Cooper S / Clubman S P0597 OBD code </a> )he specifically says that brown goes to brown and you can see that at the end the green goes into the air intake part (sorry I really don't know what that specific part is called) and this is the opposite of how they have been plugged in on my car since I have owned it.

SO what is what?!
If it helps the green one specifically has two bright yellow wires inside of it.

Hi, it's been a while and no one responded..

I've just replaced my thermostat housing (started leaking), it is a non genuine part, but I needed it quickly to get my Mini back on the road.

About the connector colours, the sensor on the top of the housing has a brown connector and this DOES have the green wire plugged into it (I have a pic).
The grey(UK spelling) plug has a grey connector in the block.

However I've not been getting any overheating warnings, or and ODBII codes.
It's been 3 weeks since replacing and the other day whilst queuing in traffic the orange check engine light came up on the dash, lost power trying to pull over to side of road. Turned off, checked coolant all ok, checked temp reading on hidden menu and about 100C/212F, was all ok on the remaining few miles home after that. I've been monitoring the coolant temp reading today and appears ok at 105C/221F..

I hope my new thermostat housing is working as designed, if not I might replace with a genuine one when I am able to get one.

Sounds like possible bad aftermarket unit. Where as it purchased ? But I would also make sure that the water pump or anything else leaking. Also those plugs at the top can get brittle break off and work loose. Reconnect them and while you are at it looks at the pins on the factory wire harness , al the plugs should clip tight into place. If they wiggle loose , then you will get a CEL code for temp sensor or a engine fault.

Got it from EuroCarParts UK. Circoli MFR.http://www.eurocarparts.com/ecp/c/MI...d303cd2&000325

I was the only place with one in stock over the weekend. The local BMW/MINI dealers were advising back order from Germany, 4 week wait and didn't have any.
No other leaking that I can see.

I've checked the cooling fan, runs ok on low speed after a few minutes with the aircon on. Relays OK and bypassing the relays the fan starts on slow and fast.

I'll check the plugs again in the morning. During UK MOT annual check, the engine is left running on the ramp to ensure the fan starts when the engine gets hot, I've left the engine running on the drive for 10 minutes when warm and the reading hovers around 100/104C, never gets hotter.

What is the other sensor for on back of the thermostat housing? (Return from radiator?)
Which sensor is the reading in the hidden menu on the rev counter?

Thanks

never heard of that part brand,

But....Rev counter is the temp sensor on top, the other plug goes to the rad and the ECU control and if for the built-in electronic valve. Check both those connections. Make sure the harness plug are connected to the actual tabs. After that still no good. I would get a replacement from that company if the connectors are fine, might just be a bad aftermarket until, even though the valve must be working as you dont overheat.

I was messing around with my ATF plug and I think I might have dislodged or screwed up the temp sensor.

Would this CEL (even when cleared) cause an emissions failure?

Should not come up as emission code. Unless you bumped some other wires also.

Just as an update, I was getting this code, replaced a lot of things but the thing that did it was swapping out the thermostat for a OEM version that was more expensive than the aftermarket housing and thermostat combined. Comparing the two, the OEM one did look far better.

I was getting this code and the fan kept being on after turning off the car.

You don't need to drain the coolant to replace the thermostat. A few tiny drops came out. My car was very cold though.

If you changed your thermostat on an R56 without draining the coolant and you didn't lose any coolant, you may be low on coolant.

@mathew,

were you able to resolve the problem? I have 2010 mini r56 turbo, the dealer replaced thermostat housing and I'm still getting P1028, not very long may be less than 100 miles. Did plugging green into green , brown into brown for thermostat sensor. Please help.

I also was getting the P0128 and 2F07 (Map Thermostat, Mechanism). I first replaced the coolant temp sensor but that didn't work, so I went and bought a new OEM Mini thermostat housing from ECS Tuning and it fixed the problem (its also on sale right now). Both codes were gone once I started it back up and re-scanned for the codes.