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7 Series - E38 (1995 - 2001)

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  #1  
Old 12-28-2010, 09:24 AM
dritchie dritchie is offline
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00 740i - Map controlled thermostat circuit/control code

I have a 2000 740i. Using a Bavarian Autosport code reader I got the map controlled thermostat circuit/control code. Is replacing the thermostat warranted here? Also should this prevent the car from starting?

Last edited by dritchie; 12-28-2010 at 09:25 AM.
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  #2  
Old 01-14-2012, 07:10 AM
kimokk kimokk is offline
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Any update on this? I have the same code.
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  #3  
Old 01-14-2012, 11:24 AM
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joyism5 joyism5 is offline
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Few things about the thermostat (map one).

The control of the engine cooling system with a conventional thermostat(regular) is determined by the coolant temperature only, while the characteristic of the map thermostat, are that temperature can now be influenced specifically within the thermostat control range.As a result the engine can be operated at a higher coolant temperature in the partial load range, on the other hand, lower coolant temperatures are intentionally set under full load operating conditions. This achieves more eficient combustion thus reducing fuel consumption and pollutant emissions.
The map thermostat is controlled by the engine control module dependent on a characteristic map, determined by the following factors: engine load,engine speed,vehicle speed,intake temperature.
The thermostat still works like conventional one (this one opens at 110Celsius degree ), however, a heating element is additionally integrated in the expansion element . In the event of control intervention by the DME control module, power (12 V) is applied to the heating element integrated in the thermostat. Heating the expansion element means that the thermostat opens at lower coolant temperatures 80- 103Celsius degrees.
The line connection and the function of the characteristic map thermostat are monitored by the diagnosis function in the DME control module. Any faults are stored in the fault code memory of the DME control module. When the coolant gauge is showing the mid-position for coolant temperature means that it reached o 75C - 113 Celsius degrees.

Knowing this , few things that will trigger the map cooling thermostat code could be :
-fault thermostat heating element,
-fault in the coolant temp sensor (the one on the thermostat housing),
-any wiring problems with the above sensor/element,
-a mechanical fault in the thermostat itself.

Any of this could cause the coolant to be out of map , and the code will be stored by the DME.

The thermostat element can be checked with a voltmeter for continuity/OHM, and if receives 12 V at the connector when temp is 73-103C. The thermostat itself can be checked using a infrared thermometer , taking values at the hose after the thermostat.

I thought this might be helpful.
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Last edited by joyism5; 01-14-2012 at 11:31 AM.
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  #4  
Old 01-14-2012, 03:54 PM
kimokk kimokk is offline
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Thanks sir! Good info to know. I guess I better do some testing. On the cluster test nr-7 it's reading normal temp: 109C. Does this mean the thermostat is working correctly?
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Last edited by kimokk; 01-14-2012 at 03:55 PM.
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  #5  
Old 01-14-2012, 04:31 PM
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joyism5 joyism5 is offline
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Quote:
Originally Posted by kimokk View Post
109C. Does this mean the thermostat is working correctly?
If the engine temp does not go over the 113C ,or if is not opening before 103C, mechanically, yes .If it works according with the map, I don't know. The question now is, if it opens when the DME is heating the element inside.

EDIT : You could watch the temp on the instrument cluster, when you cold start the engine, and check the hose after the thermostat. When the hose starts to be HOT means that the thermostat is fully open. At this time you can check again the temperature on the IC, so you will know at what temp did the thermostat start to get full open.
Mechanically the thermostat should start to be open between 103-110 C degrees . If is opening (fully) before 103C or if it stays closed over the 113C degrees, the thermostat is out of MAP range and is faulty.
The DME might intervent by opening the thermostat between 80-103C degrees. Here the heating element plays his role. You could check if the heating element is working, by applying 12V to the thermostat(not temp sensor) connection when the engine is stone cold. When applying power to it, with the engine running check if the hose after thermostat (the one that goes to the radiator) is getting warm in the same time with the engine. If it is,means that is working and you need to check the wiring. If it's not , the heating element is not working. Using a voltmeter I would make sure which one is ground and which one is positive. Use a fused wire also.
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Last edited by joyism5; 01-15-2012 at 06:23 AM. Reason: Remembered a few tips
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  #6  
Old 01-15-2012, 10:37 AM
Brummel Brummel is offline
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The thermostat in our cars can also be working ok, but on some instances have been known to leak small amounts of coolant through the heating element plug and cause the conector to short out.

Check out the thermostat electrical connector for coolant residues, the heating element should give out 12 to 12.5 ohms if working properly.
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  #7  
Old 01-20-2012, 04:55 AM
kimokk kimokk is offline
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Quote:
Originally Posted by Brummel View Post
The thermostat in our cars can also be working ok, but on some instances have been known to leak small amounts of coolant through the heating element plug and cause the conector to short out.

Check out the thermostat electrical connector for coolant residues, the heating element should give out 12 to 12.5 ohms if working properly.

I checked connenctor, wiring and ecu box no coolant residue or broken wires. How do you measure the resistance? Can you describe to me where to place my probes, on the connectors on top of the thermostat housing? Thanks.
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Last edited by kimokk; 01-20-2012 at 07:24 AM.
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  #8  
Old 01-20-2012, 06:55 AM
Brummel Brummel is offline
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Yes, set the meter to 200 ohms and test the connector on top of the t-stat.
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  #9  
Old 01-20-2012, 07:26 AM
kimokk kimokk is offline
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Thanks, do these wear out frequently? I just changed the t-stat housing (OEM) about a year ago. I thought BMW parts come with a two year warranty?
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  #10  
Old 01-20-2012, 09:03 AM
Brummel Brummel is offline
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I don't know how many years the t-stat should last, but I'm sure it should last longer than the one you replaced a year ago.

The resistance in the t-stat itself is rated at 11.5 ohms, but after testing it I get 12 ohms. I have 2 extra t-stats and they both give the same reading.

Joism5 gave you a good starting point information on how a heated t-stat works in our cars, take it from there, double check the wiring, the red/blue wire should have 12v, the DME provides ground through the brown/white wire when certain criteria is met.

Last edited by Brummel; 01-20-2012 at 09:21 AM.
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  #11  
Old 01-21-2012, 02:02 PM
kimokk kimokk is offline
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I tested for continuity and voltage on both the tstat sensor and wiring to DME. Good continuity on sensor and good voltage on positive side of wiring (this is with key in position 2). However, no continuity on ground side of wiring plug. Is this because ground is controlled by DME map and is open until set parameters are met and then switch is made? Thanks.
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  #12  
Old 01-21-2012, 05:09 PM
Brummel Brummel is offline
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You got it kimmok, that is how the system should operate. The MAP t-stat is a fail safe switch that kicks in to protect the engine from unusual high temperatures, other than that, it operates just like a regular mechanical t-stat.
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  #13  
Old 01-22-2012, 09:59 AM
kimokk kimokk is offline
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Quote:
Originally Posted by Brummel View Post
You got it kimokk, that is how the system should operate. The MAP t-stat is a fail safe switch that kicks in to protect the engine from unusual high temperatures, other than that, it operates just like a regular mechanical t-stat.

I guess the system is working normally or is there a fault in the DME? On another forum one guy says he's just lived with the code for the past two years with no other issues.
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Last edited by kimokk; 01-23-2012 at 08:26 AM.
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  #14  
Old 02-01-2012, 05:47 PM
SilbergrauBMW SilbergrauBMW is offline
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My wires on that element are fried and mines not even plugged in. I don't have a check engine light either.

There is another sensor though that's plugged in on the thermostat. Is that like a retrofit for that. Plug or is it a temp sensor. Either way my heating element is not even plugged in I found and the plug looks like absolute junk, no ses lights so I left it.
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  #15  
Old 02-01-2012, 08:11 PM
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joyism5 joyism5 is offline
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Connected on the thermostat housing has to be temp sensor and heating element. Heating element is essential for different performance reasons. I would address more attention to those wires before something gets fried.
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  #16  
Old 02-02-2012, 07:36 AM
SilbergrauBMW SilbergrauBMW is offline
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Quote:
Originally Posted by joyism5 View Post
Connected on the thermostat housing has to be temp sensor and heating element. Heating element is essential for different performance reasons. I would address more attention to those wires before something gets fried.
I'm pretty handy with electronics so I thought about fixing the plug and plugging it back in. I haven't owned the car for long so I just discovered this. I have an extra DME for some reason in my trunk, so that's another sign that says that plug may have caused issues. I'm a little hesitant right now to try and mess with it, I don't have any ses lights and I've put 500 miles on the car already
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  #17  
Old 02-02-2012, 08:23 AM
Brummel Brummel is offline
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Not all e38 are coded to throw a light when the t-stat heating element circuit is open.

SilbergrauBMW, we know you drive an e38, but for all we know it could be a m60, m62, or m62tu. Update your profile, a 325i info doesn't help at all.
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  #18  
Old 02-02-2012, 09:18 AM
SilbergrauBMW SilbergrauBMW is offline
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Originally Posted by Brummel View Post
Not all e38 are coded to throw a light when the t-stat heating element circuit is open.

SilbergrauBMW, we know you drive an e38, but for all we know it could be a m60, m62, or m62tu. Update your profile, a 325i info doesn't help at all.
325i is my wifes car, was before I bought the 1999 740il.

I'll update it later

I guess ill try to see if I can find a replacement plug off a donor car, provided the harness is okay. Is it likely if I fix the issue the sensor will leak again and short it out? Right now I've sent the cluster off to be repaired and now I've got to some down time to fix stuff.

Last edited by SilbergrauBMW; 02-02-2012 at 09:20 AM.
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  #19  
Old 02-03-2012, 09:10 PM
Brummel Brummel is offline
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If the t-stat connector shorted out the plug, it is likely to happen again unless you find the source of the problem (t-stat leaking).

My 7 did not throw a code when I unpluged the map t-stat, so I decided to use a m60 t-stat( 95F).......couldn't be happier.
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  #20  
Old 02-04-2012, 01:24 AM
SilbergrauBMW SilbergrauBMW is offline
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Quote:
Originally Posted by Brummel View Post
If the t-stat connector shorted out the plug, it is likely to happen again unless you find the source of the problem (t-stat leaking).

My 7 did not throw a code when I unpluged the map t-stat, so I decided to use a m60 t-stat( 95F).......couldn't be happier.
Im probably going to cut the plug off and shrink wrap the wires seperately and then in one sheeth and call it good.
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  #21  
Old 09-23-2013, 03:42 AM
jasone65 jasone65 is offline
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Smile Under Voltage

Sorry to revive old post, but i have searched everywhere about my problem and this is the closest related topic i can find. i have a e65. which i read everywhere the thermostat works exactly like the e38. i measured the plug its only 8v while battery measures 12.4v and this is causing one side of the hose to be extremely hot and pushing hot coolant in to the refill tank. while the left side of the hose. is perfectly cool (so the thermostat isn't opening.) i got new thermostat. and stil lisn;t working. so i;m assuming the problem is the under voltage. so i plugged the thermostat with 12v battery directly. the core heats up like a rocket, but when i plug in to the socket (8v) doesn't heat up at all. any advice?
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  #22  
Old 08-28-2014, 04:07 PM
ninetyseven1 ninetyseven1 is offline
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Quote:
Originally Posted by Brummel View Post
I don't know how many years the t-stat should last, but I'm sure it should last longer than the one you replaced a year ago.

The resistance in the t-stat itself is rated at 11.5 ohms, but after testing it I get 12 ohms. I have 2 extra t-stats and they both give the same reading.

Joism5 gave you a good starting point information on how a heated t-stat works in our cars, take it from there, double check the wiring, the red/blue wire should have 12v, the DME provides ground through the brown/white wire when certain criteria is met.
Brummel, I unplugged my map heater connector and measured voltage, key on engine off and I got 5.78V. I thought I should be getting 12V?
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