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Old 11-10-2017, 05:22 PM   #1
nu246
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Red Line OBC TEMP -128!!

Hello all,
I have lurked on this board for years now and have gained so much insight from the members posts, so firstly thanks to all who contribute. Well, I've come into a situation that has me baffled and from what I can glean from using the search, it's fairly uncommon. This morning with temps in the 50s I got to start my car and the temp gauge goes directly into, and past the red! This, accompanied with the exclamation triangle, the radiator symbol and the brake light illuminated, has me grasping for answers. First thing I did was tried to read the temp from the OBC, and to my surprise it was -128. Am I correct in assuming that this is a default or short value? So I changed the temp sensor in the thermostat--nothing! Changed the sensor at the lower radiator hose and again, nothing! Even when as far as to change the coolant level temp sensor and still-nothing. BTW had these spare parts lying around didn't just throw $ at the problem. I'll stay tuned and bump with more info as it comes up. Again, thanks for the help and all the previous advice I've gotten. ALSO, the car will start and run as if nothing is wrong. WTH

Last edited by nu246; 11-10-2017 at 05:26 PM. Reason: More info
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Old 11-10-2017, 05:26 PM   #2
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BTW last week my expansion tank burst out of nowhere, however, I assumed that it was just old, as this seems to be a common happening. It was the original exp tank. Just replaced the upper intake boot, DISA oring, cleaned MAF and ICV. This all occurred 12 hrs after driving home with no symptoms whatsoever.
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Old 11-10-2017, 05:43 PM   #3
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That's not a temp sensor in the thermostat housing, that is a heating element so the computer can open the thermostat if needed. It's otherwise a normal wax thermostat. The temp sensor is in the lower hose. Did you purge the cooling system after you replaced the expansion tank?
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Old 11-10-2017, 05:59 PM   #4
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Your car has two coolant temperature sensors One at cylinder 6 on the head (ECT) the other in the lower rad hose (CTS) YOu also have an ambient temp sensor that tells the outside air temp. Lurling for years as you state you must realize the importance of a scan tool like BMW Scanner to pinpoint the source problem. My bet is the ECT at cylinder #6 as it is the source for the OBD reading and feeds the temp needle in the cluster.
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Old 11-10-2017, 06:06 PM   #5
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Quote:
Originally Posted by turbo1168 View Post
That's not a temp sensor in the thermostat housing, that is a heating element so the computer can open the thermostat if needed. It's otherwise a normal wax thermostat. The temp sensor is in the lower hose. Did you purge the cooling system after you replaced the expansion tank?
I did purge it, following instructions posted here, and it ran fine for about 5 days with a 100 mi commute. I was referring to the element installed in the thermostat sry.

Last edited by nu246; 11-10-2017 at 06:10 PM. Reason: boneheaded reply by me
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Old 11-10-2017, 06:09 PM   #6
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Quote:
Originally Posted by BMW-North View Post
Your car has two coolant temperature sensors One at cylinder 6 on the head (ECT) the other in the lower rad hose (CTS) YOu also have an ambient temp sensor that tells the outside air temp. Lurling for years as you state you must realize the importance of a scan tool like BMW Scanner to pinpoint the source problem. My bet is the ECT at cylinder #6 as it is the source for the OBD reading and feeds the temp needle in the cluster.
Indeed I do have the scan tool, whats weird is that it isn't throwing codes. I surmise that it is the ECT. I just want some more veteran info before attempting to replace it needlessly. Are these common symptoms of a failed ECT sensor?
Thank you both for your replies.
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Old 11-10-2017, 06:13 PM   #7
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I have also read here that the fan should run for 30 seconds at startup. Is this true bc my fan is not working at all now?
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Old 11-10-2017, 07:28 PM   #8
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Not so many replies, but thanks to those who chimed in. I was able to find a post by BMW-North about this issue. Tomorrow I'll do the ETC sensor and report back. Guess i'll do the gaskets to, why not right? Here's the relevant thread if anyone else finds this thread someday. Cheers
https://forum.e46fanatics.com/showthread.php?t=980358

I'm starting to wonder if the DSC and Brake indicators are unrelated, as a few days ago I hit some unmarked roadwork, which made me feel like I was driving General Lee! the DSC light blinked but went off. Gonna check a few brake related factors, too.

LOL all this on my wife's birthday and the night before we head to the mountains to celebrate our 3 year anniversary. Geeezz The BWM will have to sit out for acting up and the Camry will have to do. YUCK!
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Old 11-10-2017, 08:16 PM   #9
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Hope this link will help, post #31 https://forum.e46fanatics.com/showthr...=929803&page=2

If you can reach and remove the plug without removing the intake, and you have another sensor, you can plug the new sensor into the harness first. That's just to verify that the wiring is good. If your gauge and lights are still acting up, it's probably a wiring problem, so no need to remove the old sensor. If it starts working, try plugging it back in to the original sensor, could be a bad connection and reseating the plug may fix it.
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Old 11-10-2017, 08:36 PM   #10
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Originally Posted by turbo1168 View Post
Hope this link will help, post #31 https://forum.e46fanatics.com/showthr...=929803&page=2

If you can reach and remove the plug without removing the intake, and you have another sensor, you can plug the new sensor into the harness first. That's just to verify that the wiring is good. If your gauge and lights are still acting up, it's probably a wiring problem, so no need to remove the old sensor. If it starts working, try plugging it back in to the original sensor, could be a bad connection and reseating the plug may fix it.
Thanks for the follow up turbo. Great advice. I'll put them both on my meter to get an idea of what's going on. I wonder if it was this fella who posted that.



I have it all apart now. Def wasn't looking forward to removing the manifold. I'll post my findings tomorrow, maybe aggregating the info here will help someone in the future. Lord knows how many all threads I've read.
BTW 202,000 miles=it's about time anyway

Last edited by nu246; 11-10-2017 at 08:42 PM. Reason: verb conjugation lol
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Old 11-10-2017, 08:56 PM   #11
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You could just probe the ECT sensor wires for resistance after unplugging the corresponding DME connector. Then compare that resistance to what it should be at your ambient temperature. Just Google or look up the ECT sensor resistance range in the Bentley manual.
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Old 11-11-2017, 05:14 AM   #12
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Quote:
Originally Posted by nu246 View Post
This morning with temps in the 50s I got to start my car and the temp gauge goes directly into, and past the red! This, accompanied with the exclamation triangle, the radiator symbol and the brake light illuminated, has me grasping for answers. First thing I did was tried to read the temp from the OBC, and to my surprise it was -128.
First I want to clarify the last sentence above. You used the Hidden OBC Menu as outlined in this thread and looked at #7 which will display the engine coolant temperature on the dash above the odometer - https://forum.e46fanatics.com/showthread.php?t=239619

Or are you referring to the Outside Air Temperature that you can display by pushing the BC button on the end of the turn signal lever?

I think the last sentence in the above quote is a red herring that has people running off in the wrong direction.

So lets remove the last sentence and re-read what happened and just take this part of your post for face value.

Quote:
Originally Posted by nu246 View Post
This morning with temps in the 50s I got to start my car and the temp gauge goes directly into, and past the red! This, accompanied with the exclamation triangle, the radiator symbol and the brake light illuminated, has me grasping for answers.
Based on what you stated above, I am starting to think this may be a cluster problem. Suggest you check out www.bmwgm5.com and depending on what you do or do not find regarding the cluster problems, email Scott and see what he has to say.

We have seen COUNTLESS cases of the temp gauge going full hot on initial start and never really seen a solid resolution posted for follow up that I am aware of. Given you had other lights come on, this is sounding like a cluster issue IMHO.

I do not know the default behavior of the temp gauge when the sensor is disconnected in the rear of the cylinder head (which is the engine coolant temperature sensor), but I would assume it would cause the temp gauge to drop to full cold?? It will do one of two things, drop to full cold or full hot, you really need a "good" car to verify this behavior.

Since you actually have a scan tool, if it supports Live/Realtime data, just look at the engine coolant temperature when the engine is cold and compare it to the intake air temperature and/or the outside air temperature. If the engine coolant temperature is correct on the scan tool, but not on the dash either by the engine coolant temperature gauge and/or the Hidden OBC Menu #7, then the cluster likely has a problem.

If the engine coolant temperature is way off, could be the sensor, wiring or possibly there could be coolant or oil that migrated up the wiring in the DME. I do not wan to send you down this path quite yet, but I have more info on this if necessary.

I am unaware if any of the DME fuses blowing could cause this problem, but it might be worth checking the 5 fuses inside the DME box as well.

FYI, the sensor in the lower radiator hose is the radiator outlet temperature sensor and this is primary used for electric cooling fan control. it does have other things is controls, but this is the primary purpose of this sensor as I recall.
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Hidden OBC Menu - Check Voltage, Temp, Fuel Level - https://forum.e46fanatics.com/showthread.php?t=239619

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Lower hose temp switch O-ring - BMW #13621743299

Last edited by jfoj; 11-11-2017 at 05:24 AM.
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Old 11-11-2017, 07:28 AM   #13
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The temperature sensor is most likely a “negative temperature coefficient” sensor. Basically, the sensor, a thermistor, decreases in resistance as its temperature increases. The gauge wil go to full cold when the sensor is disconnected.


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Old 11-15-2017, 05:43 PM   #14
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Okay guys,
Sorry for the ask and ditch, my wife and I were in the mountains celebrating our anniversary. So, I couldn't for the life of me get access to the sensor via the method in the video, so the hard way it is. I was able to remove the intake mani and replace the sensor. it definitely looked fouled. When I got it all back together, I had the same symptoms. So I slept on it and viola! When I started her up this morning, only a yellow brake light and DCS was on. Took her around the block and everything is back to normal! Is it possible that the ECU had residual capacitance stored and needed to discharge? Does that sentence even make sense?
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Old 11-15-2017, 05:46 PM   #15
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You may want to check the DME for coolant damage as well if you found that the coolant sensor was "fouled".

https://forum.e46fanatics.com/showthread.php?t=1052977

http://www.bimmerfest.com/forums/sho...21#post9977321

https://forum.e46fanatics.com/showthr...1#post16833498

https://forum.e46fanatics.com/showthread.php?t=870338
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Solve your misfires, lean codes, rough idle - https://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - https://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - https://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temp, Fuel Level - https://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose temp switch O-ring - BMW #13621743299
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Old 11-15-2017, 05:47 PM   #16
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Thanks again for the replies!
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