difference between a SWITCH and a SENSOR
03-07-2020, 07:43 PM
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Cruisin'
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difference between a SWITCH and a SENSOR
Somewhat tied into my other posts of today is a puzzle situation with Acura. I have a masters in electrical engineering, but that does not mean my paradigms are correct. Example:
Acura issue a tech service bulletin 09-012 which described a problem I had with a car I had just bought at a used car dealership. Messing with various features of the technology package on my 2009 TL with just 60K on it, I discovered the info button took me to "messages" and "all messages" and "trouble codes" and I had a message that said "check engine oil level" showing, but no "i" for information displayed between tach and speedo. Pulled over right away and oil was clean and full to top indicator on dip stick. Had no "low oil pressure indicator" light on the instrument panel. Searched for the message reset to see if message would clear and found none. Perused owners manual and similarly found nothing in there for owner to try and clear this message or others that might appear some day. Took off confident I had no problem. Got home and research here and elsewhere finding TSB 09-012 described this issue perfectly. Check oil level message set, despite oil level full. The TSB also said that in "some" cases the message might appear along with the oil pressure light on inst. panel. I did not have this error which I suspect would have triggered the service engine light. Read with my OBDII reader and no errors, either now or recently in memory. Read TSB which says "fix" for a low oil level condition is an oil pressure SENSOR mounted on top of what appears to be timing chain cover on front of engine above, but near oil filter. STRANGE. Oil level is **generally** a SWITCH (simple on/off device mounted on oil pan) and oil level would **generally** NOT be triggered by a pressure switch (Acura's word, not mine) mounted that high in the engine as opposed to a switch down in the sump?. How does one infer a lack of residual sump oil in the oil pan with a pressure switch(sensor) mounted above timing cover?? I guess you might say that if oil level is truly low that this condx. might manifest itself eventually in reduced oil pressure, but what sensor drives that big, bright yellow oil can on inst. display which signifies low oil PRESSURE. So, I am miffed where Joe or Bettie average car owner can attempt to clear messages??!!. I could have missed, but see nada either in owner's manual or my 3 thick Acura service manuals?? I received my new oil PRESSURE *SWITCH* from Acura ready to install. Before I could do that, I had to change a front wheel bearing which was quite noisy and to do so you put car up on lift, spins front wheels, blocking their rotation one at a time to isolate which side the bad wheel bearing is on. Damn Acura computer decided that my rear wheel speed sensors were bad because front wheels turning with no indication of rear wheel rotation defies their login and ASSumes both rear speed sensors became toast at same time I was changing FRONT wheel bearing. Now have 3 trouble messages set and not self clearing and no button to reset. Internet to the rescue where I learned which 3 buttons must be pressed at same time and held 5 seconds to access the "secret screens". Found low oil message was set in 2018! Wheel speed sensors set day before when I did wheel bearings. Once in this "secret screen" followed prompts, deleted 3 errors not yet to return after week of driving. WTF. Is this ploy to scare people into taking car to stealer? Aren't soft errors supposed to clear themselves after so many start cycles without seeing fault? Where did I miss seeing the instruction for Joe and Bettie average driver to not pull off highway and get car towed to stealer out of fear so that stealer can take car away from sight, push convoluted combination of buttons and pronounce car fixed! And in my world, low oil level is *generally* triggered by a switch (of a float variety) that is either made or not....on or off based on level in sump. Would that not make sense for determining oil level?? A pressure sensor is generally not an on/off device. It can distinguish between 80# of pressure and 40# or zero. Functions like a transducer. I fail to understand a pressure sensor which modulates up and down being a logical level determiner. And I would not deduce low oil level from any device mounted higher than the oil filter near top of timing cover. Does this sound like Acura technology? What am I missing? I have got to be missing something here -(
Acura issue a tech service bulletin 09-012 which described a problem I had with a car I had just bought at a used car dealership. Messing with various features of the technology package on my 2009 TL with just 60K on it, I discovered the info button took me to "messages" and "all messages" and "trouble codes" and I had a message that said "check engine oil level" showing, but no "i" for information displayed between tach and speedo. Pulled over right away and oil was clean and full to top indicator on dip stick. Had no "low oil pressure indicator" light on the instrument panel. Searched for the message reset to see if message would clear and found none. Perused owners manual and similarly found nothing in there for owner to try and clear this message or others that might appear some day. Took off confident I had no problem. Got home and research here and elsewhere finding TSB 09-012 described this issue perfectly. Check oil level message set, despite oil level full. The TSB also said that in "some" cases the message might appear along with the oil pressure light on inst. panel. I did not have this error which I suspect would have triggered the service engine light. Read with my OBDII reader and no errors, either now or recently in memory. Read TSB which says "fix" for a low oil level condition is an oil pressure SENSOR mounted on top of what appears to be timing chain cover on front of engine above, but near oil filter. STRANGE. Oil level is **generally** a SWITCH (simple on/off device mounted on oil pan) and oil level would **generally** NOT be triggered by a pressure switch (Acura's word, not mine) mounted that high in the engine as opposed to a switch down in the sump?. How does one infer a lack of residual sump oil in the oil pan with a pressure switch(sensor) mounted above timing cover?? I guess you might say that if oil level is truly low that this condx. might manifest itself eventually in reduced oil pressure, but what sensor drives that big, bright yellow oil can on inst. display which signifies low oil PRESSURE. So, I am miffed where Joe or Bettie average car owner can attempt to clear messages??!!. I could have missed, but see nada either in owner's manual or my 3 thick Acura service manuals?? I received my new oil PRESSURE *SWITCH* from Acura ready to install. Before I could do that, I had to change a front wheel bearing which was quite noisy and to do so you put car up on lift, spins front wheels, blocking their rotation one at a time to isolate which side the bad wheel bearing is on. Damn Acura computer decided that my rear wheel speed sensors were bad because front wheels turning with no indication of rear wheel rotation defies their login and ASSumes both rear speed sensors became toast at same time I was changing FRONT wheel bearing. Now have 3 trouble messages set and not self clearing and no button to reset. Internet to the rescue where I learned which 3 buttons must be pressed at same time and held 5 seconds to access the "secret screens". Found low oil message was set in 2018! Wheel speed sensors set day before when I did wheel bearings. Once in this "secret screen" followed prompts, deleted 3 errors not yet to return after week of driving. WTF. Is this ploy to scare people into taking car to stealer? Aren't soft errors supposed to clear themselves after so many start cycles without seeing fault? Where did I miss seeing the instruction for Joe and Bettie average driver to not pull off highway and get car towed to stealer out of fear so that stealer can take car away from sight, push convoluted combination of buttons and pronounce car fixed! And in my world, low oil level is *generally* triggered by a switch (of a float variety) that is either made or not....on or off based on level in sump. Would that not make sense for determining oil level?? A pressure sensor is generally not an on/off device. It can distinguish between 80# of pressure and 40# or zero. Functions like a transducer. I fail to understand a pressure sensor which modulates up and down being a logical level determiner. And I would not deduce low oil level from any device mounted higher than the oil filter near top of timing cover. Does this sound like Acura technology? What am I missing? I have got to be missing something here -(
Last edited by wmliedtke; 03-07-2020 at 07:51 PM.
03-08-2020, 09:39 AM
#2
Instructor
After looking into the diagram of the Low Oil Pressure Indicator circuit, it is indeed a switch and not a "sensor" that measures/transmits specific values of anything. If the oil pressure is high enough to close the switch, everything is good.
(Diagram is the same for the Tech models with keyless entry, just the normal ignition is swapped with the push button ignition circuit.
Regarding the switch location, it's connected directly to the oil pump itself (not sure of the actual manifold design within the pump and rocker arm oil control solenoid to see where the switch fits within the oil flow). Seems as though that switch is there to help determine whether the oil pump itself failed, or if there just isn't enough liquid in the system to maintain the pressure needed to activate it.
And honestly, you've gone farther than I've ever attempted to delete the old fault messages from the list (I never figured it out). I'd just accepted that anything in the list that isn't currently causing an active fault (with a gauge indicator lit up) is an old message that either I've addressed or still need to address at some point.
(Diagram is the same for the Tech models with keyless entry, just the normal ignition is swapped with the push button ignition circuit.
Regarding the switch location, it's connected directly to the oil pump itself (not sure of the actual manifold design within the pump and rocker arm oil control solenoid to see where the switch fits within the oil flow). Seems as though that switch is there to help determine whether the oil pump itself failed, or if there just isn't enough liquid in the system to maintain the pressure needed to activate it.
And honestly, you've gone farther than I've ever attempted to delete the old fault messages from the list (I never figured it out). I'd just accepted that anything in the list that isn't currently causing an active fault (with a gauge indicator lit up) is an old message that either I've addressed or still need to address at some point.
03-08-2020, 12:51 PM
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Cruisin'
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What an awesome response. Thank you sir! Few things. What source provided those great diagrams? I find the 3 very thick "Acura service manuals" quite lacking in detail that at least I can't find. Example would be to simply address the message center messages and why you could get a check engine oil level message which I now understand (thanks to your answer) is derived from really a loss of sufficient oil pressure as seen by the oil pump and NOT have a corresponding low oil pressure light on the instrument panel. Guess whatever feeds the "yellow oil can" light on instrument panel is triggered in "real time", while message center messages could be 5 years old and just never go away. That seems very misleading. Say you are low on oil, see the message, and add oil. All is good, but message does not clear. So 4 mos. later or whenever, you run low on oil again. Since "old" message never clears, you could be low and disregard the message as having already being taken care of. Guess you will have to ignore message center and put faith on light on instrument panel. Google "Acura message reset" and there are U-tube videos explaining how to clear old messages. Essentially, depending on your car's year, you must be on "confirmation page" on Nav screen and you push either a combination of 3 buttons simultaneously and hold for 5 seconds. Video said to push "cancel" + "maps" + "info" and hold all 3 until hidden menu comes up. On my year car I needed to push (IIRC) "cancel" + "maps" + "menu". Best to view a video as another screen appears and you must choose right option there to be taken to next screen where deletion can occur. You must delete each message, one at a time. Neat thing is that there are options to see what was in car's history so you can see what says a previous owner encountered. Say you bought car used and prior owner had crashed it. You would likely see a dozen or more messages such as many tire pressure sensors triggering, ASC errors, lots of messages. Each message will be date stamped so you can know exactly when that message was set. You have option to clear a message or to clear all message history which will make all prior messages be gone forever. There is also a button you don't want to select which will "reset" fault system and may render the message center useless. Read before you make selections! Prompts are very clear and easy to follow. Don't select any prompt which is not clear to you. You can also, from this hidden menu, see each system on you car and its current state of health. You can view entire ABS/ASC system, SRS system, emissions system, etc. Gives info down to individual sensor level. Knowing how to access this hidden menu is a MUST in my opinion for all Gen4 Acura owners. Find any of several u-tube videos available. Search by "how to reset Acura message center messages" or similar.
Ok on pressure switch truly being a switch. Seems cheesy to me. If you are over 40 or 50, recall those gauges we added to our cars to look cool! The SUN brand oil pressure gauge, tach, oil temp, etc. Properly functioning oil pressure gauge might very well read 20# at idle and 60# or more a speed. Would 20# of oil pressure be "ok" while doing 70mph? Hell no. So, when you select a "switch" to sense oil pressure, would you select one that trips at 20#? No, cause then it would come on all the time at idle. How about 10# or 5#? Do you really want to wait on an idiot light to tell you that you only have 5# of oil pressure. Modern logic DEMANDS that software takes into account more than just pressure, but what pressure at what rpm.? An oil switch only says I'm real thirsty as I can't get any water so I'm dehydrated and sick! And even though I drank a gallon of water, I will keep telling you I'm still thirsty as there is no way to reset me!! LOL At least Acura could have used ignition switch cycles without condition present to clear error. One day longer before finding how to clear message and I would have spent $100 plus $35 for the oil pressure switch I now have based upon TSB 09-012 which describes this check engine oil level fault as very common and way to fix is to replace switch. I would have spent $135 and STILL has message, unless I went to Acura dealer (closest is 75 mi. away) who would charge me twice that, but had smarts to use reset menu to clear message. A regular mechanic or you or I doing TSB recommendation would buy new switch, do the work, and see no difference....
Ok on pressure switch truly being a switch. Seems cheesy to me. If you are over 40 or 50, recall those gauges we added to our cars to look cool! The SUN brand oil pressure gauge, tach, oil temp, etc. Properly functioning oil pressure gauge might very well read 20# at idle and 60# or more a speed. Would 20# of oil pressure be "ok" while doing 70mph? Hell no. So, when you select a "switch" to sense oil pressure, would you select one that trips at 20#? No, cause then it would come on all the time at idle. How about 10# or 5#? Do you really want to wait on an idiot light to tell you that you only have 5# of oil pressure. Modern logic DEMANDS that software takes into account more than just pressure, but what pressure at what rpm.? An oil switch only says I'm real thirsty as I can't get any water so I'm dehydrated and sick! And even though I drank a gallon of water, I will keep telling you I'm still thirsty as there is no way to reset me!! LOL At least Acura could have used ignition switch cycles without condition present to clear error. One day longer before finding how to clear message and I would have spent $100 plus $35 for the oil pressure switch I now have based upon TSB 09-012 which describes this check engine oil level fault as very common and way to fix is to replace switch. I would have spent $135 and STILL has message, unless I went to Acura dealer (closest is 75 mi. away) who would charge me twice that, but had smarts to use reset menu to clear message. A regular mechanic or you or I doing TSB recommendation would buy new switch, do the work, and see no difference....
03-08-2020, 01:43 PM
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Cruisin'
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Still want to know where you found these excellent diagrams.... My car is keyless entry and has technology package, so wonder if my schematic might be little different? Your diagram shows oil pressure switch sending inputs to a module which I assume considers more conditions than just oil pressure switch (N/C). The module outputs to what I assume is hard error oil can light on instrument panel. Does not show how that switch can set a MESSAGE only that never clears and NOT the oil can light. Would like to see the permissives that when "true" trigger the message center to indicate and error MESSAGE is present. I bet a dollar when this message set originally on my car prior to me owning, that message appeared, but so did the yellow oil light in instrument panel. Owner remedied the oil situation and yellow light extinguished, but message lingered on for all eternity or until U-tube was discovered!! Internet is source of good and a ton of BAD misinformation but the key is in knowing the difference. Had Acura not had a TSB that exactly describes this common problem, I would never have even thought of replacing a perfectly good switch with another. I would have concentrated first with how to reset messages to see if it came back. Never has.... YMMV
03-08-2020, 01:45 PM
#5
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Yep, I agree, the simplified switch isn't anywhere near as useful as a pressure gauge would be. I consider the Low Oil Pressure indicator to be the "Oh, shit" light, since that's the appropriate reaction to seeing it while the engine is running lol. There also doesn't seem to be any sensor to provide real-time pressure data to the onboard computers, so part of the troubleshooting of a Low Oil Pressure indicator is to check the continuity of the switch, and if the switch is fine, manually check the actual oil pressures to make sure they're within spec (10 psi at idle, 71 psi at 3000rpm).
Regarding where those circuit diagrams and component layouts came from, they're from the "official" service manual originally published by Honda, and someone made it downloadable as a .pdf file here:
http://www.mediafire.com/file/lmhmpo...TL_SM.pdf/file
A lot of it contains clickable links that take you to whatever section you're looking for (in either Volume 1 or Volume 2), and some of the clickable links that are intended to take you to a specific page seem to be missing or incorrect, but you can manually tell your pdf reader to move to (example) page "22-506". I expect you'll find this manual extremely useful.
Regarding where those circuit diagrams and component layouts came from, they're from the "official" service manual originally published by Honda, and someone made it downloadable as a .pdf file here:
http://www.mediafire.com/file/lmhmpo...TL_SM.pdf/file
A lot of it contains clickable links that take you to whatever section you're looking for (in either Volume 1 or Volume 2), and some of the clickable links that are intended to take you to a specific page seem to be missing or incorrect, but you can manually tell your pdf reader to move to (example) page "22-506". I expect you'll find this manual extremely useful.
03-08-2020, 02:18 PM
#6
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LOL! Diagram you posting and the PDF link are from the same manuals I bought. Published by Honda, they are gray in color. First 2 volumes are about 2" thick each and volume 1 and 2 address mostly mechanical and electrical issue in a fairly general way, especially as pertains to the electrical. I also bought the 3rd manual which is called "electrical trouble shooting" and is also quite thick, filled with detailed sensor information, schematics, etc. I did not see the diagram you posted as I don't look at those pages as my car is keyless entry and your diagram is for "without keyless access". Might be identical to my pages, but missed somehow. At least Acura appears to use a switch with two sections...one which goes false at 71 psi and one segment of the switch goes false (open) at 10 psi. The module must look at rpm and so the switch inputs a module which takes rpm into account and would not accept 10 psi as "ok" at higher rpm. Still begs the question why Acura will not facilitate user reset or clearing of messages if they have reason to believe they are in error, old, problem remedied, etc. which would be VERY helpful rather than telling you to take car to Acura, and by the way we happily provide an app for the display which will cheerfully locate the nearest ACURA dealer to wherever you are!! Gee, thanks. I can forget the vacation, drive out of my way to that nearest Acura dealer, drink free coffee and wait and wait for a tech. to come and push 3 buttons and send me on my way without hotel money for that night. I thought BMW was bad about that. For 12 years, I called upon my German heritage and my English engineering degree to put over 200,000 miles on my 2002 540 which never saw a BMW dealer except to get my faulty Takata air bags replaced free of charge... German engineering was very difficult to troubleshoot without benefit of high-end diagnostic stuff they use, but their THOUGHT PROCESS was extremely sound...right down to using plastics in critical areas that by design would not fail before about 6 years so lease owners and owners that trade up every few years would never have trouble, but keep OLD and down-trodden BMWs off the road as much as possible. Must have learned that part from us..
03-08-2020, 02:34 PM
#7
Instructor
LOL! Diagram you posting and the PDF link are from the same manuals I bought. Published by Honda, they are gray in color. First 2 volumes are about 2" thick each and volume 1 and 2 address mostly mechanical and electrical issue in a fairly general way, especially as pertains to the electrical. I also bought the 3rd manual which is called "electrical trouble shooting" and is also quite thick, filled with detailed sensor information, schematics, etc. I did not see the diagram you posted as I don't look at those pages as my car is keyless entry and your diagram is for "without keyless access". Might be identical to my pages, but missed somehow. At least Acura appears to use a switch with two sections...one which goes false at 71 psi and one segment of the switch goes false (open) at 10 psi. The module must look at rpm and so the switch inputs a module which takes rpm into account and would not accept 10 psi as "ok" at higher rpm.
But yeah, I agree that making it more difficult than it should be to delete those diagnostic error messages sucks for anyone who wouldn't know any better than to look into the issues before dragging themselves off to the dealership for potentially unneeded repairs...
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