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Discussion Starter #1
Simple question, does a bad thermostat affect the MAF's in any way, I got code P0128 and believe the thermostat is stuck open. I also used DavidS MAF test calulator to get a 125 corrected for L/H on the test 4 in the secret menu.

I know I got to check maintenance records to see if the MAF's, and fuel filter have been replaced anytime soon so I just want to rule out if the thermostat affects the MAF's thanks
 

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I dont see why a bad t-stat would cause MAF problems, but a bad t-stat would certainly throw codes. I used to get the 'coolant temp plausibility' code before i replaced my t-stat.

Maybe the gurus have other insight?
 

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I can't see how a bad t/s would affect the MAF's but it may affect the l/h reading as the DME will see the engine as being cold and richen the mixture. So the 125 l/h you saw maybe would be even lower if if the engine was up to temp. (This assumes the open-loop, WOT look-up tables actually compensate for a cold engine.)
 

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Discussion Starter #4
125 l/h was at WOT with a fully warmed up engine. It warms up properly and the gauge sits at 11 o clock. It just takes a while to get there. Before correction for baro pressure, temp and altitute etc, it read 105 l/h.
 

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The best way to check for an iffy thermostat first off is to check the ktemp in the OBC, free and easy, doesn't require the reading of codes, and will give you an idea of whether it is working. Codes may be thrown but the ktemp figure is the best start off, before you believe you have a faulty tstat. Your temp gauge looked OK, and taking a while to warm isn't neccesarily a bad tstat, could be quality (condition, age, dilution, genuine coolant or not) of coolant etc.
 

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No problem at all, but these cars throw plenty of issues in their time, and if you can cross off something that's not really bad, then it leaves more for the other things.

Like I said, worth checking before taking it further. The accepted wisdom is a pretty steady 79 degs (mine is a steady 64-64 and therefore does need doing), this is what the thermostat should hold the coolant at, but there's more written about thermostats on here than nearly anything else, so fill your boots. Second only to oil ;)
 

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Also keep in mind there are other things that MAY impact the MAF reading, such as a VANOS not working correctly. For example if the camshaft advance is slow or not working correctly, it SHOULD be difficult for the engine to draw the correct amount of air, therefore registering lower than expect MAF readings on your specific engine if the VANOS is not working correctly. I have not seen this first hand, however, theory indicates it is possible. If you could swap MAF's onto a known good car, then you could be totally sure of the readings.

Also with the the MAF sensor, they also have an integrated barometric sensor that I believe may be the weak point in these sensors and may be the major cause of many "soft" failures? I had a friend that worked for a Bosch affiliate here in the US in the early 80's that had high power microscopic pictures of the barometric sensor portion of these types of sensors. There is a very tiny inverted dome on the silicon and somehow sealed. I saw many pictures of how the seal between the microscopic dome and silicon fails. For some reason the Bosch sensors have had issues since their inception.
 
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