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Discussion Starter #1
Hey guys, I'm having a bit of a strange issue with my 2001 325xi.

I first started getting this P0128 code that suggests that my thermostat might be stuck open. I looked it up on the forums and then found that i should probably replace the Thermostat, so I got myself an eBay thermostat (no temperature rating) for around $20. After replacing it, i drove it around for about 3 days, and the code came back on. I cleared the code, and again, the code shows up later. So i look up what else i could have done wrong, and i find myself getting the sensor that goes on top of the lower radiator hose. I replace that and clear the code, but it pops up again.

I end up getting the more expensive Wahler Thermostat that's rated at 97c (celcius) (207 Farenheit) because i thought that maybe the eBay one was built to a different spec or something. So i replace it and same story.

After i installed the Wahler Thermostat, I hooked up my OBD2 reader and monitored the coolant temperature reading. I started it up, and then the temperature rose fairly quickly (while driving) up until 108c (226F), then it dropped down to around 75c~80c (167F ~ 176F), which told me that the thermostat had opened up. and I thought, cool, it worked! But the next day, cold start, temp starts climbing, but much slowly and it never goes past 80c (176F), so that's when the DREADED P0128 code pops up again.

It felt like that the thermostats are all getting stuck open and not closing again.

I also read that there are other coolant temperature sensors on the block, could those be preventing the thermostats to close? if so, do i need to replace both? which one gives the reading to the thermostat? is this thermostat not controlled by immediate temperature alone (like other conventional ones?

Any advice would be greatly appreciated.
and if you have any questions or have advice on something i could do to help diagnose this, i would gladly make videos or take pictures as well.

Thank you for your time.
 

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See this is your first post, so I will go easy on you.

First things first, the P0128 code is usually pretty accurate and an indicator that there is a problem.

The $20 thermostat was a BAD idea, but is not in the car now, so we will move on.

Be careful what you read, the temperature sensor in the lower radiator hose likely had no impact on the P0128 code what so ever.

Hold off replacing any more parts at this point.

These engines should run consistently around 96C. The fact that your engine got up to 108C is a bit troubling. Did you properly bleed the cooling system?

The engine never getting above 80C is a problem and this is why you are getting the P0128 code.

How much did you pay for your Wahler thermostat and where did you get it?

Do you now if the water pump has ever been replaced?

Does this car have the factory radio?

What OBDII tool do you have and can you generate Log files with it?

Suggest you also read this thread - http://forum.e46fanatics.com/showthread.php?t=964491

There may be more to cover, but need to get some initial info from you.
 

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Ok, that question has me stumped. Was it an easter egg to see if we're paying attention? :hmm:

Edit: Wait, I think I got it. If the radio has been replaced then the HVAC may have been hacked up?
You made me laugh the first sentence, I figured there may be questions, but I did not want to go down the road of explaining why a non factory radio may be a problem.

But there are 2 temperature sensors behind the radio. One for the AC evaporator and one for the heater core. If these sensors get screwed up/disconnected (mainly the one for the heater core) it can command the thermostat heater on full time and cause the engine to run too cold.

The simple check is just disconnect the connector on the thermostat and see if the temperature gets warmer, if so, then there is a problem that is commanding the thermostat heater on that needs to be traced.

I do not think this is the case in this situation, however, we will find out more when the OP responds.
 

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2004 330Ci 85k miles
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You made me laugh the first sentence, I figured there may be questions, but I did not want to go down the road of explaining why a non factory radio may be a problem.

But there are 2 temperature sensors behind the radio. One for the AC evaporator and one for the heater core. If these sensors get screwed up/disconnected (mainly the one for the heater core) it can command the thermostat heater on full time and cause the engine to run too cold.

The simple check is just disconnect the connector on the thermostat and see if the temperature gets warmer, if so, then there is a problem that is commanding the thermostat heater on that needs to be traced.

I do not think this is the case in this situation, however, we will find out more when the OP responds.
I didn't know that the heater core temp sensor values made their way to the DME to influence the engine thermostat heater. I thought they were only read by the IHKA for internal air control.
 

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Some sort of "safety" feature to keep the heater core temperature from getting too high. If the heater core gets too warm, it will enable the thermostat heater.
 

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Discussion Starter #7
See this is your first post, so I will go easy on you.

First things first, the P0128 code is usually pretty accurate and an indicator that there is a problem.

The $20 thermostat was a BAD idea, but is not in the car now, so we will move on.

Be careful what you read, the temperature sensor in the lower radiator hose likely had no impact on the P0128 code what so ever.

Hold off replacing any more parts at this point.

These engines should run consistently around 96C. The fact that your engine got up to 108C is a bit troubling. Did you properly bleed the cooling system?

The engine never getting above 80C is a problem and this is why you are getting the P0128 code.

How much did you pay for your Wahler thermostat and where did you get it?

Do you now if the water pump has ever been replaced?

Does this car have the factory radio?

What OBDII tool do you have and can you generate Log files with it?

Suggest you also read this thread - http://forum.e46fanatics.com/showthread.php?t=964491

There may be more to cover, but need to get some initial info from you.
First of all thank you for your brief response, I wasnt able to respond right away because i've been pretty busy, but today I made sure to bleed the system of any air bubbles right after starting it up.

Initially after replacing the thermostat, I believe i might have had some air in the system and that's why it got so hot. But After today's cold start, that didnt happen.

I got the thermostat off of my shop's parts distributer IMCparts.net and paid around $50ish USD.

I got the car around 6 months ago and i am not sure if the water pump has ever been changed.

and i still have the factory radio.

Here's a video i recorded of the coolant temp as my car started. I sped it up but i put a timer so that you could possibly follow along. while i was recording and the car was warming up, that code pops up again.

So i think that the car is taking longer than usual to warm up, it never reaches 96C.

It likes to stay between 86C and 90C as you can see in the video.

link: https://youtu.be/dCwczNBQmk0
 

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You need to learn how to use the Logging feature in your App, it is FAR easier and more accurate that what you are tying to do.

I see you have Torque, its an OK App, however, I prefer OBDFusion. It is only $3.99 and $1 cheaper than Torque Pro last I checked.

I have not bothered to do a write up about Logging with Torque, but it is similar to OBDFusion.

Suggest you read the PDF in this link - http://forum.e46fanatics.com/showthread.php?t=1097893

I do not want to comment until I can see the bigger picture with a decent Log because there are so many other variables that may impact the engine coolant temperature.

Also post the associated Freeze Frame data for the P0128 code.

The problem may be a simple as replacing the thermostat again or something slightly more complicated to resolve.
 

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Discussion Starter #9
You need to learn how to use the Logging feature in your App, it is FAR easier and more accurate that what you are tying to do.

I see you have Torque, its an OK App, however, I prefer OBDFusion. It is only $3.99 and $1 cheaper than Torque Pro last I checked.

I have not bothered to do a write up about Logging with Torque, but it is similar to OBDFusion.

Suggest you read the PDF in this link - http://forum.e46fanatics.com/showthread.php?t=1097893

I do not want to comment until I can see the bigger picture with a decent Log because there are so many other variables that may impact the engine coolant temperature.

Also post the associated Freeze Frame data for the P0128 code.

The problem may be a simple as replacing the thermostat again or something slightly more complicated to resolve.

Hey thank you for taking your time again, I got the app and played with it a bit to get the setting all right. I'm a bit confused on the dropbox side of things. I use it on my pc and phone, but the instructions read that I can't have it installed? is this correct? Should i uninstall the app from my phone and the software from my pc before i do any logging?
 

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Hey thank you for taking your time again, I got the app and played with it a bit to get the setting all right. I'm a bit confused on the dropbox side of things. I use it on my pc and phone, but the instructions read that I can't have it installed? is this correct? Should i uninstall the app from my phone and the software from my pc before i do any logging?
If you already have a DropBox account, this is not a problem.

I just WARN people that have never used DropBox to be careful because DropBox can and will start mirroring your files and if you have a sizeable number of files, your "Free" DropBox account will be QUICKLY filled up and you will be prompted to purchase more DropBox space.

This is all configurable, but most people do not need or want more BLOATWARE operating in the background on their computer.

So if you already have a DropBox account, just go into the App and enter your DropBox credentials, typically your email address and your DropBox password.
 

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Discussion Starter #11
You need to learn how to use the Logging feature in your App, it is FAR easier and more accurate that what you are tying to do.

I see you have Torque, its an OK App, however, I prefer OBDFusion. It is only $3.99 and $1 cheaper than Torque Pro last I checked.

I have not bothered to do a write up about Logging with Torque, but it is similar to OBDFusion.

Suggest you read the PDF in this link - http://forum.e46fanatics.com/showthread.php?t=1097893

I do not want to comment until I can see the bigger picture with a decent Log because there are so many other variables that may impact the engine coolant temperature.

Also post the associated Freeze Frame data for the P0128 code.

The problem may be a simple as replacing the thermostat again or something slightly more complicated to resolve.
Okay, I got the three logs needed. Thank you for your time and help.

https://www.dropbox.com/sh/cupo36d1og4gp0o/AAD1Oad8Sxc2J6q0aqKkVS1Ca?dl=0
 

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I am not sure you should be so worried about the P0128 code for the moment!!

Not sure what is going on with your engine fuel management system, but in ALL Logs the System Fuel Status is in mode 8 or in ERROR. The engine is not running in Closed Loop fuel management control.

I am not exactly sure where to tell you to start looking for the problem

What I can tell you is it appears the O2 sensors are working well enough for the moment and I do not think these are the root cause of your problem.

The MAF reading appears to be under reporting slightly, this may be due to a vacuum leak that would need to be ruled out first. But again, not sure this is the root cause of the current problem.

I would start with checking the fuses inside the DME box and also verifying the O2 sensors are connected to the proper engine bay connector.

See my comments here - http://forum.e46fanatics.com/showpost.php?p=17079127&postcount=41
 
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