ABS Speed Sensor Errors W639 Viano

[Nigel Griffiths]

Hi People

I have an V6 petrol Viano 3.2 (2004) (Just to get round ULEZ in London). I had a newer 2.2 version but sold it, as it didn't comply. Off it went to Botswanna or somewhere in Africa.

Anyway ever since I brought it, the ABS triggers at very slow speeds say, usually around 5-10 mph. You can drive through and it clears. On a MBII reader it never really stores a fault code. Once going into the Automatic Transmission Section, it did store a code say implausible speed reading on rear left. I had the speed sensor replaced, but it still does it. I thought that it must be a rusty reluctor ring, but ringing up Mercedes for a new ring, I found out that there isn't a separate ring on the drive shaft but the wheel bearings have magnetic sections on them that produce the pulse speed.

Reading various forums on the subject, some people advise that get the tacking done, as this could the issue. Other than that, does anyone know whether the magnets fail in the bearing or get covered in corrosion. it going to be a hell of job just to replace a wheel bearing for annoying abs issue at low speed.

any thoughts anyone?

 

[Blobcat]

Hello and welcome

Does it have standard wheels on? Same size front and back?

Implausible speed can be because of different speeds on the wheels due to different rolling circumference.

 

[Nigel Griffiths]

Hi Blobcat,

Thanks for the reply. It has the standard 17" wheels factory finished. What I have also noticed is that the speedo drops to nil when its doing it. Does anyone know whether the speedo gets it speed reading from the wheel sensors, or is the gearbox speed sensors?

When looking at the speed reading on the automatic transmission section on MB11, the front axel speeds drop to Nil as well as the speedo.

Whats really annoying is I cant drive it for a 2 to 3 mins on purpose making it trigger, the ASR light flashing, but there are no errors on the MBII reader.

 

[Blobcat]

ABS rings not giving a consistent speed reading is pretty common

 

[Nigel Griffiths]

Sorry there was slight typo on the last reply. It should have read, I can drive it for 2 to 3 mins at 5mph. making the ASR light flash and there are no errors on the scanner stored.

Its really odd. Under the automatic transmission scan on front axel speed, the speed reading drops to 0 mph when the ASR light is flashing. Trouble is when you go into the ESP section of the scanner it turns off the ABS, BSA and ASR module, so I cant get it to do it, and I haven't really noticed the live speed data for each of the sensors vary that much, unless you turn of course.

Thanks for your help.

 

[Nigel Griffiths]

Actually thinking about it, its the warning triangle light, that flashes on, if there is a ASR light it doesn't come on. It obviously warns that the traction control is working, so thinking about it, it must be a wheel speed sensor, (or reluctor ring) and the ASR is getting a bad signal, thinking that one of the wheels are spinning. But I cant understand by the speedo would drop to zero.

 

[LostKiwi]

The speedometer uses the wheel sensors to derive speed.
You should be able to view the live data from the wheel sensors via a suitable diagnostic scanner. Sometimes the reluctors can rust and get dirty which will send a bad signal and gives similar symptom.

 

[alexanderfoti]

Yes there won't be faults as the car doesn't think there is a fault. Only that normal slippage is occurring. If you read the live values whilst it's doing it. It should confirm which sensor it is (as you suspect rear left anyway)

Corroded rings are common and are available on their own on the aftermarket (check eBay etc).

 

[Nigel Griffiths]

Thanks guys, the only thing is on a viano, there are no seperate reluctor rings, the magnets are built into the back face of the wheel bearings.

I have a icarsoft mbii scanner, and as i say the live data doesnt really show much, trouble i havent got a long enough straight road to travel at 5mph. Could do with finding a runway somewhere

 

[LostKiwi]

I have an MB2 and I'm sure you can get live data from the wheel sensors.

 

[Big Cheese]

Change the wheel speed sensor,don't use aftermarket,use OEM & the problem will clear.

 

[Nigel Griffiths]

Hi

I have an MB2 and I'm sure you can get live data from the wheel sensors.

Hi Lost Kiwi,

On the Viano section (under Sprinter) on the MBII scanner, you can view the OB2 live data from the wheel speed sensors, trouble is, this section in under the ESP section, and soon as you go into that mode on the live data, it switches off the ABS system, and the ASR system, and the BAS system. However, it does give out the wheel speeds, but it happens at such low speeds, you cant tell which one is giving out faulty readings.

I'll think I will have to get the wife to drive it, when Im looking at the scanner.

Many thanks

 

[Nigel Griffiths]

Change the wheel speed sensor,don't use aftermarket,use OEM & the problem will clear.

Hi Big Cheese,

I thought it was the rear left sensor and that was giving out dodgy readings, but I changed the speed sensor with OEM sensor for MB main dealer and it didn't cure the problem. They are £90.00 a pop, and it includes the brake wear sensor wiring harness as well.

I don't really want to buy new sensors for the two fronts, and then it turns out to be faulty magnets to the wheel bearings.

Many thanks though.

 

[Big Cheese]

If you can get it on a diagnostic machine with live readings as Lost kiwi says it will tell you which wheel is the problem.
I had the same problem with my 639 vito & after a check with a diagnostic with live readings found which wheel was the culprit.A aftermarket sensor was fitted & didn't fix the problem but a OEM one did.

 

[Nigel Griffiths]

Thanks Big Cheese. The MB11 scanner does show live wheel speed data, Ill give it go.

Were the problems with your Vito at low speed?

 

[Big Cheese]

My problem occurred from pulling off,put the van straight into limp mode.
I changed three hubs thinking it was the magnet as I bought the van with this problem & it turned out to be the aftermarket sensor that was fitted.
A OEM sensor cured the problem in my case.

 

[Nigel Griffiths]

My problem occurred from pulling off,put the van straight into limp mode.
I changed three hubs thinking it was the magnet as I bought the van with this problem & it turned out to be the aftermarket sensor that was fitted.
A OEM sensor cured the problem in my case.

Ok thanks for the heads up. Just got try identify which speed sensor it is.

 

[Nigel Griffiths]

Hi All,

Just thought I would post an update on the ABS error. In the end, I brought one new merc rear sensor and two new bosch AM speed sensors. Took it to the local indie garage who replaced them for me. however, they kept on getting worse errors on ABS and light was staying on. On star they couldnt program the speed sensor correctly. He looked into the merc rear sensor and thought this was the wrong part. Ordered a new one from merc, fitted that, still had worse errors. He thought then it was the abs pump and module, so brought second hand one on ebay. However, all seemed fine, apart from when turning corners, ABS light flashed up. The Front and rear speed sensors were reading different speeds. Started looking into the new front Bosch speed sensors, and he put one of the old front ones back in and he managed to get the correct speed reading on that one. So ordered a new speed sensor from mercs for the other side. All back up and running now without the low speed error.


What we think the problem was, was a defective ABS control module, nothing to do with the speed senors. Thinking about, in the first place the scanner did not indicate different speed reading on any of the speed sensors, so they were all reading correctly. That cost me few quid with wrong parts, and new speed sensors from mercs. So beware, its not always the speed sensors. If you can get a cheap relatively good ABS module from Ebay, I would have replaced that first, then start replacing speed sensors.

 

[LostKiwi]

Incidentally the magnets on the wheel bearings are built into the oil seal and are a relatively simple job to replace. A common problem is that people fit a new seal and press it too far into the hub.

 

[italiano]

Change the wheel speed sensor,don't use aftermarket,use OEM & the problem will clear.

Hi Big Cheese, just wondered if I could ask what problem you had before replacing and after fitting the aftermarket wheel sensor (not the OEM)?