A good day to diode

Zep

Moderator
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9,110
My car has been in to Christian Lewis for a service and a few other bits including a diagnosis on an intermittent no MSP and ABS light problem.

I was worried it was a wheel bearing / sensor, but apparently these are all fine on the SD3. Communication with the ABS module is a bit iffy apparently which is either the bridge can or the dreaded diode.

From reading previous threads the most likely location of the diode is near the fuse box or in the cable run next to the trans tunnel. Has anyone found it anywhere else before I start pulling it apart?

Thanks!

Zep


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MAF260

Member
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7,662
Those are the 2 most common places for the diode; the third is apparently somewhere behind the dash near the heater (according to Russell at Autoshield). The diode location should be marked by some red tape on the loom. Despite finding nothing on SD3 initially you may well find its a wheel bearing - I did!
 

Zep

Moderator
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9,110
I think I'd prefer the bearing, at least then it's a simple fix!

Ed is trying an update on his SD3 before making the final call, hopefully all sorted for Brunty!


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Kyle4200

Junior Member
Messages
251
Hello, I think I may have a similar problem - my speedo doesn't work - the No ASR light is on, when plugged into a SD2 system it doesn't pick up any known faults, just an engine maintenance message (Bosch ABS/ASR 5.3) saying the ABS/ASR in passive mode, BLS off and ASR not switched off by driver, the speedo works fine as I've had it out and tested it, the bridge can is also fine as I swapped it with another, when using an ScanTool I can see road speed while driving, that with the fact there's not an ABS light on I can see the wheel sensors are okay, when I unplugged the 5.3 module itself I get a No ABS, EBD, ASR and transmission light come up so I think thats all working to, so it can only be a communication error on the wiring loom through a loose connection or blown diode, how did you get on?
 

allandwf

Member
Messages
10,958
I had this on Mrs allandwfs Merc. it was a chaffed wire to a rear sensor. Took ages to find. Had to get it on diagnostics when it was up, and that pointed me in the right direction. Hoping for an easy fix.
 

Zep

Moderator
Messages
9,110
As it turned out, the update on the SD3 sorted out the communication and it was a poorly wheel bearing. My wheel bearing was on the rear so it caused a NO-ASR and an ABS light.

I don't envy your having to pull out the loom, I hope it isn't too painful!
 

Kyle4200

Junior Member
Messages
251
I was worried it was a wheel bearing / sensor, but apparently these are all fine on the SD3. Communication with the ABS module is a bit iffy apparently which is either the bridge can or the dreaded diode.

Hello Zep, when you say communication with the ABS module was abit iffy what do you mean, I see on there it can read faults for wheel speed sensors and mine showed okay, apart from this engine mainatainance message I had basically telling me the ASR wasn't switched off by the driver and the ABS/ASR was in passive mode? Both Mike at Maserati Shed and Emblem have used their diagnostic software on it and came out with the same result, I remember Mike saying it was a strange one as I had a very early 4200 so he used 3200 program for some things. Speedo still out, ASR still off and the Trip computer is not working.
 

Zep

Moderator
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9,110
As I understood it, he was able to connect to the ABS module and read speed outputs from the wheels which appeared ok, but he couldn't see faults on the module. As it turned out it was a software issue as when he updated his SD3 the faults were visible and it was a wheel sensor failing intermittently.

Having a little read, this passive mode might be a red herring as it may just indicate the type of wheel speed sensor. But I could be wrong.

If the trip computer isn't working and the speedo is also not working then on the face of it there is no speed signal from the ABS module so there could well be an ECU fault. Maybe there is some mileage in finding a Bosch service agent and having them test the ABS ECU directly to see what is happening in there.
 

Kyle4200

Junior Member
Messages
251
As I understood it, he was able to connect to the ABS module and read speed outputs from the wheels which appeared ok, but he couldn't see faults on the module. As it turned out it was a software issue as when he updated his SD3 the faults were visible and it was a wheel sensor failing intermittently.

Having a little read, this passive mode might be a red herring as it may just indicate the type of wheel speed sensor. But I could be wrong.

If the trip computer isn't working and the speedo is also not working then on the face of it there is no speed signal from the ABS module so there could well be an ECU fault. Maybe there is some mileage in finding a Bosch service agent and having them test the ABS ECU directly to see what is happening in there.

I see, maybe the dealer could take a look first - ideally they have the latest version of SD3 (I believe it was only the SD2 used at both places that checked), the thing is when I plug in my own obd ScanTool I can see the speed signal and how fast I'm going when driving, also when I disconnected the module itself I had a No ASR, ABS, EBD and gearbox (cambiocorsa) light come on telling me some if not all the systems are working in the module. I want it to be a loose connection or this diode you mentioned as I have a electrician/engineer working on it this weekend.
 

Rex B

Member
Messages
657
As it turned out, the update on the SD3 sorted out the communication and it was a poorly wheel bearing. My wheel bearing was on the rear so it caused a NO-ASR and an ABS light.

I don't envy your having to pull out the loom, I hope it isn't too painful!

U
 

Rex B

Member
Messages
657
Sorry must have pressed wrong key when reading thread, hope you get your problems sorted, I had some frustrating problems when I first had my 3200 and decided I had to either spend some money with someone who would sort the problem or sell the car as it was spoiling the driving experience.

Rex B
 

Zep

Moderator
Messages
9,110
I see, maybe the dealer could take a look first - ideally they have the latest version of SD3 (I believe it was only the SD2 used at both places that checked), the thing is when I plug in my own obd ScanTool I can see the speed signal and how fast I'm going when driving, also when I disconnected the module itself I had a No ASR, ABS, EBD and gearbox (cambiocorsa) light come on telling me some if not all the systems are working in the module. I want it to be a loose connection or this diode you mentioned as I have a electrician/engineer working on it this weekend.

If you can see a speed signal on the k line then it could be wiring, it's so hard to say. The speed output will be a pulse signal, so someone with a oscilloscope and some knowledge might be able to find the issue. Once again I wish you luck!