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P0720 code?

20K views 70 replies 10 participants last post by  Noodles 
#1 ·
Anybody ever received this code P0720 Output Speed Sensor? I cleared it yesterday and the CEL is on again...I'll bet it's the same fault. How much would I be looking at?
 
#2 · (Edited by Moderator)
700 and 720



I see this is a very old post but don't see any follow up so I will post my question and see what turns up.

Our '99 ML320 sort of conked out yesterday but my wife got it home.

My simple scanner gave me codes 700 and 720. This happened before, maybe 2 years ago and for some reason putting in a new MAF fixed it??

Anyhow after that I had the dealer do the transmission cable adapter change even though it wasn't called for on our car. I thought I would need a new transmission control module but after I saw where it was I decided to not replace it. In any case the problem went away. Now the problem is back/

Anyhow, now I can clear those codes and then simply start the engine and the codes are back, the engine limps, the whole thing. You don't have to move the car to set the codes so I hope it is an engine speed sensor and not the control unit.:confused:
 
#3 ·
Update - Disconnected the MAF and the engine behaves nicely. Also at first the 700 and 720 codes didn't come on so I plugged the sensor in and it still ran nicely, but codes 700 & 720 show up again, all this with the car in park.

I get a 110 code with the sensor disconnected, that's to be expected.

Seems to me that 2 years ago a new MAF fixed everything.

I may try to drive it to an indi with it un-plugged.

Sadly I can't remember the exact sequence of what I did 2 years ago but am pretty sure the new MAF fixed everything.
 
#4 ·
If my memory serves me correctly that's a transmission code. The speed sensor detects the revolution of the idler gear parking pawl lock gear and emits a pulse signal. The pulse signal is sent to the Transmission Control Module (TCM) which converts it into vehicle speed. I believe that you will find this code stored in two places the engine and the transmission control modules. One can be erased easily but the code clearing in the transmission control module will require a more advanced scanner/reader. You want this checked out quickly and my belief it's the transmission conductor plate as that is a common problem with the 722.6 trans along with wicking of fluid and connector failure (rubber rings start leaking). You want this addressed asap since if you let it go you may find your vehicle unexpectedly going into limp mode, characterized by being stuck in second gear and clunking or jerking when shifting from park to drive or reverse. I do not believe it to be the MAF. Read the codes because the moment you started the car without the MAF connected you threw another code and MAF performance or failure is independent of the transmission issues. Good luck.
 
#5 ·
700 and 720 and MAF



A mystery . . . and your memory is accurate. When this problem occurred before I had the same symptoms . . . Feb 2014. I still have the old part and the invoice.

I looked back and found that in Feb 2014 I had rough running and the two codes 700 and 720. I found that I had replaced only the MAF and the problem went away. That's the only thing I did. I did have the local MB dealer replace the connector adapter around the same time, even though they insisted that car was not on the recall (whatever it's called) list. I knew that similar transmissions were on the list. [I bought 2 adapters, one still sitting here for my '98 SL500 which has a similar transmission. It will also soon get a new transmission filter I have on hand, a job already done on the ML.]

I did do a lot of worried checking but the MAF was the only thing I did. It's really hard to believe the MAF could cause codes 700 and 720 but it almost certainly did back then, and maybe now.

What I do remember in 2014 is that the problem started a few seconds after I did a fairly brisk acceleration after getting it back from the dealer, forgot why it was there. I can call them Monday and see what work they did and when. It may be that my acceleration test (didn't tell my wife, it's her car) caused some dirt to get to the MAF. Even so, why do those two codes keep getting re-set on a car sitting in park?

I cleaned and then replaced the MAF but still don't remember how I got to that point. Whatever happened, the problem went away a year.

I do see some references about cleaning the air induction system and filter when the MAF is replaced. I also see they have gone up in cost.

Thanks for the response. I can't reconcile why the MAF replacement got rid of those two codes.:confused:
 
#6 ·
Quick update. I decided to rely on past experience even though it doesn't make sense to me. I ordered a new MAS for $22.50 which is a good gamble.

I paid $26.99 for the one I bought in Feb '14 and it apparently cured the same symptoms I have now, at least for a year.

The problem is that I'm a retired engineer/physicist with 60 years experience and am acting against all logic!
 
#10 ·
ML320 sluggish and stalls



Yes, I agree. I bought one just over a year ago for about $29 and it, for some reason, fixed the problem and the 700 and 720 codes. I can't imagine why but it did happen. I was on the edge of buying a new TCU or other expensive part but I'm pretty sure the MAS fixed it, not sure why.

I do know that unplugging the MAS greatly improves the problem.

If the $22.50 unit fixes the problems it's a cheap diagnosis and I could feel confident in buying a rebuilt one for $150 or so. I decided that, based on my experience in 2014 that $22.50 is cheaper than driving into any repair facility.

I plan on cleaning the entire air induction system while I wait for the part.

I wish I could determine where the engine speed sensor is located and how to replace it. It's a suspect, however I think it may determine ignition timing, not sure. If it does then the engine should not even run if it'a the problem.

Anyhow, thanks for the response .. It's appropriate:nerd
 
#9 ·
I actually had transmission conductor plate failure. But it didn't just fail immediately it was progressive over a two year period. It started with the trans not going into gear right away. Then check engine light would go on and I would use a primitive scanner (invested in a SnapOn ultra now) to erase the code in the ecm but not realizing that the code was stored in the tcm as well. That "cured" (if you will) the problem for a period of time. But it then started again. Missing an interstate exit and upon backing up approx 15 ft. on the berm and shifting to drive the car wouldn't move but when I shut it down on restart it was fine. No CEL but I knew it wasn't right. Then pulling into a parking space at a supermarket and upon shifting from reverse to drive again nothing and no CEL. Restart then it was fine. But then I went to a meeting and upon leaving the car clunked, the CEL came on and the car stayed in second gear. Nothing, not restart not clearing the CEL fixed it. In fact I would clear the code start the car and as soon as I moved the shifter lever from park to any gear the CEL would come on. It was the information on this forum and the assistance of 43sqd that helped me diagnose and correct the problem and when the SnapOn was connected and the tcm was accessed there was a list of codes (all relating to the conductor plate failure) as long as my arm that was cleared. You need to get a good quality scanner and get into the transmission. I'm sure when you access the tcm you'll find codes from back to the time of the first incident that was concluded to be the MAF. Have you ever changed the "sealed for life" transmission fluid? Now is the time to change the fluid, filter in addition to whatever needs to be addressed inside. There are actually kits that contain the conductor plate, connector, gasket and filter, all OEM for sale on EBAY. Mine was from a Florida Mercedes Dealership. I've learned that properly maintained these transmissions are truly bulletproof but like everything maintenance is the key. Good Luck.
 
#11 ·
ML320 sluggish, stalls at low speed

I actually had transmission conductor plate failure. But it didn't just fail immediately it was progressive over a two year period. It started with the trans not going into gear right away. Then check engine light would go on and I would use a primitive scanner (invested in a SnapOn ultra now) to erase the code in the ecm but not realizing that the code was stored in the tcm as well. That "cured" (if you will) the problem for a period of time. But it then started again. Missing an interstate exit and upon backing up approx 15 ft. on the berm and shifting to drive the car wouldn't move but when I shut it down on restart it was fine. No CEL but I knew it wasn't right. Then pulling into a parking space at a supermarket
and upon shifting from reverse to drive again nothing and no CEL. Restart then it was fine. But then I went to a meeting and upon leaving the car clunked, the CEL came on and the car stayed in second gear. Nothing, not restart not clearing the CEL fixed it. In fact I would clear the code start the car and as soon as I moved the shifter lever from park to any gear the CEL would come on. It was the information on this forum and the assistance of 43sqd that helped me diagnose and correct the problem and when the

(snip a bit)

SnapOn was connected and the tcm was accessed there was a list of codes (all relating to the conductor plate failure) as long as my arm that was cleared. You need to get a good quality scanner and get into the transmission. I'm sure when you access the tcm you'll find codes from back to the time of the first incident that was concluded to be the MAF. Have you ever changed the "sealed for life" transmission fluid? Now is the time to change the fluid, filter in addition to whatever needs to be addressed inside. There are actually kits that contain the conductor plate, connector, gasket and filter, all OEM for sale on EBAY. Mine was from a Florida Mercedes Dealership. I've learned that properly maintained these transmissions are truly bulletproof but like everything maintenance is the key. Good Luck.
Thanks - The fluid was changed some time ago (Now at 66,000) and I did have the adapter plug changed, even though the dealer said it was not necessary on that model. I also had the transmission filter changed by the dealer, using parts I supplied. (Interesting that a dealer would do that but they did.)

I have no transmission problems at all, just an engine that responds poorly, stalls, etc. when sitting in the garage in "Park".

I like your logic but just cannot link a sluggish, stalling engine, sitting in park in the garage, to a 700/720 code set. Also, the engine performance is better with the MAS disconnected.

I have an intermediate quality diagnosis tool and it can erase codes and gives a text description, but nothing beyond the first 3 digits of the codes.

Thanks again . . .:crying
 
#15 ·
That transmission reset won't clear the transmission code. You need a star system or higher end scanner. As for the issue your trans set a code. It is most likely the conductor plate. The reason it didn't clear is because it got bad enough that it was set in the TCU as well as the ecu. You can take it to the indie and if he has the scanner he can clear it but until you address the root cause it will be back and so will limp mode. When I finished mine I had a list of pending TCU codes as long as my arm and originally I would clear them and they would stay cleared for months only to come back because I didn't clear the TCU. It's a learning process. The transmission is getting worse that's why when it finally locked the code you can't clear it. Good luck.
 
#16 ·
Transmission codes



Thanks, appreciate the wish-

I could clear the code and "reset" the transmission but it came back whenever I drove the car, while it was still hot.

Looking at the situation, I think it's related to the temperature of the transmission. Worked fine when I got the engine problem fixed and during the first drives, but on next drives it returned and became a problem again. I haven't tried it again on a cold transmission because I don't want to deal with another immediate disappointment.

What seems really strange is that the MAS/MAF and transmission problems occurred at the same time, this week and in Feb of last year. Last year resetting the transmission and clearing the codes after replacing the MAS lasted a year.


I tend to believe that when I set up the cold car on Tuesday for the drive to the shop it will clear, and I hope shift properly, at least for 18 miles. In any case I am prepared to drive it down there in low gear at 30 mph. The shop does have a scanner that can read far beyond what mine does.

Anyhow, does anyone agree with the temp theory?

My fear is that it's the conductor plate that's expensive and time consuming.:(
 
#18 ·
Codes P0700/P0720



Thanks,

I had the dealer put in a new adapter plug and a new filter last year. The socket adapter wasn't a recall item but I insisted it be done anyhow. Don't know about a magnet but it sounds like a good idea if the transmission is opened. The socket adapter was one I bought from Arizona and I saw one comment that sometimes the O-rings aren't tight.

I have just had to keep searching for what causes those codes and have found many different possible reasons, ranging from trivial to major, the major being the conductor plate and/or TCU.

I guess I'll find out on Tuesday. Strange that I cleared the codes and had two good test runs today, with several engine starts during each. After telling my wife that everything is O.K. (Same as last year) I decided to make a final run but the problem existed from the start.

Warm transmission or what?
 
#21 ·
P0700/P0720



The shop called today after I sent them a copy of the previous posting. They said to not bring the car down as long as the CEL stayed off. I really don't know what to make of that nor do I know what harm may come of it if the speed sensor does indeed fail completely.

My understanding is that the car will go into limp mode and have to be driven in low gear.

I have no way of knowing how deep my simple scanner goes, but it seems to me that if the CEL is off all codes and pending codes must be off. Also, there is another set of readings telling me how well certain systems are responding. The scanner says everything is O.K.

The history of all this is that the last time it happened it stayed good for a year.
 
#22 ·
A pending code is just that a pending code. It's waiting to happen. And your scanner doesn't read or clear TCU codes. When the sensor fails (and it will fail) you are going to need to deal with the vehicle wherever it is when it fails and limp mode. Your choice. The fact that the mechanic told you not to bring in the vehicle after the code hit but was reset knowing it was a P code (and can't be cleared from the TCU with a standard scanner) speaks volumes about the mechanic. Either he doesn't know or does know but doesn't want to deal with your issue. Left as is its a handgrenade with a lose pin. And when it goes off get ready for limp mode and a wrecked day. Good luck.
 
#23 · (Edited by Moderator)
P0700/P0720

A pending code is just that a pending code. It's waiting to happen. And your scanner doesn't read or clear TCU codes. When the sensor fails (and it will fail) you are going to need to deal with the vehicle wherever it is when it fails and limp mode. Your choice. The fact that the mechanic told you not to bring in the vehicle after the code hit but was reset knowing it was a P code (and can't be cleared from the TCU with a standard scanner) speaks volumes about the mechanic. Either he doesn't know or does know but doesn't want to deal with your issue. Left as is its a hand grenade with a lose pin. And when it goes off get ready for limp mode and a wrecked day. Good luck.
Thanks for the analysis-

Right now no pending codes, no CEL on the car in question, a '99 ML320.

What's interesting is that last year and again this year the codes were set simultaneously with a MAS failure. In both cases the replacement of the MAS caused the codes to clear and the CEL light to turn off, accompanied by correct shifting.

Also, last year, after the car returned to normal operation, the local MB dealer replaced, upon my request, the transmission connector adapter and transmission filter. As part of this process they did a full scan and told me that all codes at all levels were clear.

The Star DTB Bulletin, T-B-27/48e, (look it up), did not include this car but I was concerned that there just might be fluid wicking up to the TCM and the dealer agreed to perform the procedure specified by the bulletin as well as replace the transmission filter. The adapter part # is A203 540 01 53.

There was no wicking but I just wanted to be sure so I had it done.

I will have the system scanned at some point but in the interim the car will not be driven on highways and will not be driven distances that cannot be returned from in a limp mode.

I cannot generate a link between the MAS failure and the transmission events but am absolutely sure they occurred at the same time, and the initial sign was near engine failure which was fixed enough by disconnecting the MAS that the car could be driven. If anyone can link those to events, please pass along your observations.

In the mean time I'm watching the power steering pump on the '98 SL500, which I rebuilt myself two weeks ago. So far, no leaks, no noise.
 
#27 · (Edited)
Your understanding is correct. The P in front of the code has nothing to do with "pending". It means Powertrain.
Pending code means there is a intermittent fault. The ECM has picked up a "fault", but if the fault doesn't recurr a certain number of times it wont "mature" into a stored/active code & it would be cleared from the memory..........

Do you really think the car being in limp mode is not a major problem??? The car gets in limp mode to protect itself. It means there is a serious problem, which you have to rectify.
 
#28 ·
Pending and Limp



Thanks for the clarification-

The car is not in limp mode and neither the local MB dealer nor my indi want to see the car until it shows a code or CEL. I still have a call in to the dealer to discuss past history on this car. I want to have them, once more, confirm that they have a record of a clean full scan when they did the transmission socket and filter replacement in March, 2014. They last time I talked to them they simply told me they had done transmission service and had replaced the connector adapter and filter. I didn't specifically confirm that they had actually done a full scan when I last called, only got a reading of the service description by a support lady, not a service advisor.

The mystery to me is why, in Feb 2014, and again in Mar, 2015, those two codes, P0720/P0700 came up when a MAS failed and cleared shortly after I got the engine running smoothly by replacing the MAS, the second MAS was a "cheapie", costing only about $25, free shipping, bought simply as an aid to diagnosis.

Is there any way to link the unstable engine situation to creation of those codes, twice in 13 months?
 
#29 ·
In my opinion the code in the TCU can and does remain in the TCU once it's set there until cleared. And once set the cel goes on and stays on. It can be reset but the first time you move the shifter lever to any gear from park you get a jerk as it goes into gear and the cel comes back on.
 
#32 ·
TCU/CEL



Thanks,

No jerk, no CEL, no codes. We are going to drive the car locally until we see something happen. The dealer doesn't think we should bring it in as long as it's well.

I also did several changes into and out of low range. Did so just as described in the owners manual.
 
#31 ·
vvrj, if there is a intermittent fault its like a viscous cycle.........it clears after a number of cycles , then its back again......& so on & so forth........It will continue being pending until the sequence of the fault increases, then it will become a stored/active/current fault.
 
#33 ·
Art it would seem that it is only a matter of time until the pending code sets itself. Mine did just that. Ran for almost a year doing stupid but non offensive things until the code didn't clear and set. Then all hell broke lose. Changed the conductor plate and cleaned it up she runs great now.
 
#34 ·
Exactly...... while the fault was "minor" the code was pending....until the fault got serious & the code become current/stored & all hell broke lose........& the current code will never clear unless the fault is fixed, in your case the replacing of conductor plate.......
 
#35 ·
Pending



Ours ran just perfectly for 13 months or so, no problems at all.

What I am still trying to sort out is why each incident happened when the MAS failed and the engine became unstable. I disconnected the MAS both times and the engine ran fairly well. After the MAS was replaced with a new one the P codes went away.

There just has to be some causal relationship between a mis-behaving engine and the P codes showing up.

I'll bet that someone on this forum will find that connection.
 
#38 ·
No OVP in 1999 ML320



Thanks, I didn't know that.

About the MAS I still have the notion that the erratic engine surges, which went away by first disconnecting, and then replacing the MAS, might have triggered the power train codes.

No proof, just a link to the two identical events 14 months apart.
 
#42 ·
New Codes


Thanks for the documentation. I can almost follow the logic chart but am stuck at step 1, not having a vacuum system. As far as I can tell the two panels are to be read as if they are connected. The photo is good but the .pdf has tiny print and the "Great New" Acrobat reader "DC" doesn't have an obvious expand feature that was on the version I had before Sunday. I'm sure the new version does have a way to change size so I'll continue to see how it works.

I have everything downloaded so I'll see how it goes from here.

Thanks-
 
#48 ·
Not if the codes were present at the time the scan was done. If the trans acted up after you left the dealer and left the codes they won't be on the printout, but it is worth looking at the printout to see if there were any trans codes. If there are and the dealer did not clear them correctly then you certainly have the right to have that done as the dealer did not do it correctly the first time.
 
#49 ·
Transmission Codes



The 3-page printout was supposedly done before the codes were cleared. The "active" codes don't show up on my scanner but the P0720 and the P0700-106 codes are on the printout as well as the mixture codes which are:

P0173-134 and P0170-023. Those two codes are marked as the ones that triggered the CEL. I cleared them when I got home an put in a temporary low cost MAS and the new Bosch MAS will be here in a couple of days. My scanner just gives/gave me P0173 and P0170 (sometimes) and lets just say the mixture codes are not an issue.

The issue is that I can still get, on my basic scanner, P720 and P0700, which are bothersome.

There were many STORED codes, all starting with C, that I can be sure were caused by work I did on the car over time. For example, I replaced a trashed stop lamp switch and can be sure that failure set a code.

Anyhow, I will call the service guy and ask him to verify that the two transmission codes were cleared AFTER the printout. Also, I have looked up the date I got the transmission socket adapter and try to see whether the transmission codes came up before or after that work was done.

I just checked my AutohausAZ purchase history and the two transmission socket adapters, filters, and transmission fluid were ordered on 3/6/2014.

The dealer did the ML right away but the SL parts are still here waiting to be done. For the SL500 I have to see whether I really need engine mounts, which would take priority.
 
#51 ·
chhs, you are failing to understand that all P07xx codes are, in actuality , transmission codes reported through/via the ECM Module. Look at the list of the trans. codes that I previously supplied.

The only reason M/B does this is because there is no separate/individual warning light as there is for ABS, Air Bag, etc. So if there is a problem with the transmission, the trans. module (ETC Module) recognizes that problem and then sends a signal to the ECM to illuminate the CEL and report that problem under a P07xx code number.

But as you can see from the supplied list, not every 3 digit code has a corresponding ECM P07xx code attached to it, which means that there could be a problem with your transmission but the CEL light will never illuminate. Pretty slick by M/B.

So in essence, you as a novice/DIY'er will always need a scanner to read the 3 digit codes stored in the ETC, Module whether the the CEL is illuminated or not.
 
#52 ·
As an occasional visitor to this forum, I'm following this thread with interest as:

a) my W209 CLK uses the same (or very similar) N3/10 and N15/3 modules as the OP's ML320, and I could get this same transmission fault one day.

b) It's proof that a little knowledge can be a 'misleading' thing. I know we all want to use DIY to solve our car problems, but for complex faults we are stuffed without the essential tools and the information on how to use them. :)
 
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