Hi everyone,

Last year in October my local dealer replaced differential in my DBS (MY 2011). All went smooth, so right after the exercise I put my car for wintering. After opening a new season 2021 I realised my cruise control switches off at 55mph+ speed.

Hmm, put my car back to my dealer. It appears there was a difference in speed readings between ABS system and differential (?) The gap is increasing with the speed and at 55mph it exceeds the tolerance, so no cruise control is possible and P2162 is logged.

My dealer seems to be a bit confused. They confirmed the new diff is the right one for my DBS and as per their knowledge, no calibration of speed sensor is possible. Any suggestions more than welcome as the season has started and my car has been homeless for over 4 weeks. Thx!

 

just a WAG (wild-assed-guess).... but because the diff and the ABS must match, as you imply, and the diff is right according to the dealer, i'd be looking at the ABS sensor, assuming the rear brakes were involved in a diff replacement. but to be honest. a quick look should be enough to see if it was even connected back up, if it was indeed ever disconnected.

 

Thank you 61mga for the suggestion, however I assume ABS reads all 4 sensors from each wheel, so rear must match the front since no ABS codes are present. In the meantime dealer has also replaced the diff sensor - no improvement. Diff ratio is 3,46 as per the spec. That all looks weird unless there is a calibration procedure which no dealer knows :-(

 

i would still venture a guess that they didn't connect something (i'm an optimist )... anyway, i found some info on P2162 that may help...

"If your OBD-II equipped vehicle has stored a code P2162, it means that the powertrain control module (PCM) has detected a discrepancy between two separate vehicle (output) speed sensors. The individual vehicle (output) sped sensors have been designated as A and B. The sensor designated as A is normally the forward most sensor in the network but check specifications for the vehicle in question before reaching any diagnostic conclusions. In the type of system intended to exhibit a code P2162, multiple vehicle (output) speed sensors are used. It is likely that one is located in the differential and the other is situated near the output shaft housing of the transmission (2WD) or transfer case (4WD). The vehicle (output) speed sensor is an electromagnetic sensor which is mounted in close proximity to some type of toothed reluctor ring wheel or gear. The reluctor ring is mechanically affixed to an axle, transmission/transfer case output shaft, ring gear, or driveshaft. The reluctor ring spins in conjunction with the axle. As the reluctor ring teeth pass within thousandths-of-an-inch of the output shaft speed sensor, the magnetic field completes the sensor input circuit. The notches between the reluctor ring teeth create interruptions in the same circuit. These completions/interruptions occur in rapid succession as the vehicle rolls forward. These circuit completions and interruptions create wave form patterns that are received by the PCM (and other controllers) as vehicle speed or output shaft speed. As wave form pattern speed increases, estimated vehicle and output shaft speed increases. Likewise, as the input speed of the wave form slows, estimated vehicle or output shaft speed decreases. The PCM is constantly monitoring vehicle (output) speed when the vehicle is moving forward. If the PCM detects a variation between the individual vehicle (output) speed sensors that exceeds the maximum threshold (for a set amount of time) a code P2162 will be stored and a malfunction indicator lamp (MIL) may be illuminated."

from: https://www.obd-codes.com/p2162
i think you may be right that the new diff may need to be synced with something inasmuch as it may involve the odometer reading and god forbid THAT should be involved in any tomfoolery!. (haha) but absence of ABS codes may be a red-herring seeing that there is no mention of it in the description of the code, just the speed sensors. anyway, good luck.

 

Thank you for this. The thing is that up to 55MPH all works fine, which suggests all signals are present, however the discrepancy is getting higher and higher until it reaches the critical level, where PCM is getting upset and switches off the cruise circuit :-(.

 

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you could perhaps replace the two rear wheel ABS sensor ??

Question please :
Why did you replace the diff of your DBS ?
Thanks

https://www.obd-codes.com/p2162

 

thread reads like a poor-man's "The Adventure of the Dancing Men" by conan-doyle. let us know how this turns out.

 

I thought this was a place where people exchange their experience and seek for help/suggestions. Hmm, perhaps I was wrong. I am sorry to bother you.
BTW, I decided to replace the diff as it was tooo noisy. I am quite conservative and uncompromised when it comes to my own astons.

 

Since the sensors all seem to be working, perhaps the new toothed wheel that the differential sensor is reading has a different number of teeth than the one removed?
Perhaps there was one (or more) teetth damaged during installation resulting in an incorrect pulse value?
This would give an different count/pulse reading as the speed increases. A one tooth in forty difference is about a 2.5% error.
Just a thought.

 

This makes perfect sense since diff speed is lower (ca 10%) than ABS and the replaced sensor was a bit chipped, thanks. The dealer has started serious investigation with AML assistance, so all should be clear soon. Thank you everyone for the contribution.