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Speed Sensor Issue--P 0721 Code

Old 01-05-2019, 12:54 PM
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2009 ML 350 4Matic Gas 65K Miles/2003 E320 Sport 60k Miles
Speed Sensor Issue--P 0721 Code

Driving this morning I sensed a slight acceleration as I braked prior to a turn and shortly after the brakes applied themselves as I was driving and after idling at a red light it took some RPMs to get the car moving as it felt like the brakes were applied.

I scanned when I got home and got a P0721 Generic Pending Output Speed Sensor Circuit range/performance code.

It's a 2009 ML 350 w/66k miles and I do have a basic warranty sill active, but it covers the major power-train and engine parts.

I do not believe the speed sensors will be covered.

Is this a major repair? Take it to my local MB guy or if this is a bigger issue and falls under the power-train should I take this in to the dealer shop? I have no idea on the possible range of repairs or costs.

Thanks in advance for your feedback.
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Old 01-05-2019, 01:48 PM
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Do you have a 350 Gas, 350 CDI or 350 BlueTec?

Please UPDATE YOUR PROFILE in USER CP to indicate the correct model.
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Old 01-05-2019, 02:31 PM
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It's a 2009 ML 350 4Matic gas.
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Old 01-06-2019, 12:49 AM
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Is the ESP light on?
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Old 01-06-2019, 08:32 AM
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No, no warning lights at all this time. This had previously happened 2 weeks ago, the ABS ESP inoperative lights came on but after sitting for 1-2 days the warnings were gone and the issue did not occur again until yesterday.

The first time when the warnings appeared, it was almost unnoticeable when driving, the brakes did not apply themselves as they were doing yesterday.
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Old 01-06-2019, 09:27 AM
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When the unwanted braking occurs it is a clear indication that there is a problem with the Yaw Rate Sensor.

I do not know what code reader you have, but you need a scanner type reader which can read the codes in every module (approx. 25).

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Old 01-06-2019, 11:27 AM
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Thanks for your time and help.

I have the iCarSoft MB II Scanner and I believe it can scan by module.

I drove it a bit last night no issue and this morning I was on the exact same route as yesterday. On the way there no issue whatsoever but on the way home the exact same issue at oddly the exact same point of the return route. Started with a slight acceleration on it's own, difficulty accelerating from a stop and then the bakes applying themselves.

However this time I did get the warnings lights and message: ABS, ESP Inoperative See Operator's Manual.

Once the warning came on the car did not apply the brakes itself while I was driving but the car did still strain in accelerating from full stops.
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Old 01-06-2019, 12:17 PM
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Then you must read the codes in the ESP Module.
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Old 01-06-2019, 01:55 PM
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Thanks, the ESP scan returned 8 codes:

5116 Right front speed sensor--------check installation position
6002 Supply voltage too high (overvoltage)
6001 Supply voltage too low (undervoltage)
5132 right rear speed sensor-------check wheel bearings
5135 right rear speed sensor-----Implausible wheel speed
5134 right rear speed sensor ----Clean multipole and replace if necessary
7270 Implausible values from RPM sensor rear axle
5399 CAN signal 'Gear Selected' from control unit---N15/3 (etc [EGS] control unit) is implausible
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Old 01-07-2019, 01:21 AM
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Originally Posted by dmico2 View Post
Thanks, the ESP scan returned 8 codes:

5116 Right front speed sensor--------check installation position
6002 Supply voltage too high (overvoltage)
6001 Supply voltage too low (undervoltage)
5132 right rear speed sensor-------check wheel bearings
5135 right rear speed sensor-----Implausible wheel speed
5134 right rear speed sensor ----Clean multipole and replace if necessary
7270 Implausible values from RPM sensor rear axle
5399 CAN signal 'Gear Selected' from control unit---N15/3 (etc [EGS] control unit) is implausible
Clear all the codes in the ESP and take it for a short drive and see what codes return. Then post those codes.
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Old 01-11-2019, 07:40 PM
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After driving it for several days without issues or codes tonight I noticed when coasting he car accelerated on it's own and then when accelerating from from a stop it felt like brakes were slightly applied. No warning lights or msg appeared on the dash

I scanned and two codes popped up.

Transmission Control Module

0721 Transmission output speed signal implausible when compared to wheel RPM signal

ESP

5399 CAN signal 'Gear Selected' from control unit---N15/3 (etc [EGS] control unit) is implausible


Thanks again for your help.
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Old 01-12-2019, 03:54 AM
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Have you replaced the right rear speed sensor?

See if those initial codes are still stored.

I believe that the 0721 code is being stored because the trans. is recognizing that there is a speed sensor issue, namely the right rear wheel speed sensor.

If the Output Speed Sensor in the trans. was defective, the appropriate code would be stored

Last edited by Maj. Dundee; 01-12-2019 at 04:56 AM.
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Old 01-12-2019, 11:48 AM
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Thanks for your continued help.

No, I have not had a sensor replaced.

The initial codes are not stored. The only two codes that the car is throwing is 0721 from the transmission and 5399 from ESP.

I drove the car this morning without issue, still no warning lights or message.

It is a big difference cost-wise if this is a simple sensor issue versus the conductor plate.
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Old 01-12-2019, 03:26 PM
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Originally Posted by dmico2 View Post
Thanks for your continued help.

No, I have not had a sensor replaced.

The initial codes are not stored. The only two codes that the car is throwing is 0721 from the transmission and 5399 from ESP.

I drove the car this morning without issue, still no warning lights or message.

It is a big difference cost-wise if this is a simple sensor issue versus the conductor plate.
Wait a while and carry your scanner with you. As soon as there is a problem, read all modules but do not shut off the engine.

Or the alternative would be to replace the R/R Wheel Speed Sensor.
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