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Abs Warning Light And Speedo Not Working


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#1 GrahamV

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Posted 23 January 2014 - 06:24 PM

Hi,
The ABS warning light has come on and the speedo has stopped working ( plus management light)
I have read the diagnostic codes and get P0500 and P0121.

From what I have googled, I am guessing it is likely to be a speed sensor but would this be on one of the wheels, or on the gearbox? Would I have both?
Also I have looked up the P0121 code and it refers to "Throttle Position Sensor Switch". I have absolutely no idea what this might be. Can anyone shed any light?

Many thanks, Graham

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#2 jeebowhite

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Posted 24 January 2014 - 09:29 AM

Basically, the ABS system operates as the speed sensor. It constantly monitors the wheels and relays the data to the ECU which calculates the speed. Given that you have no speed at all, I would say that you may be looking at an ABS Module issue, or a duff sensor. Ordinarily the code reports what sensor is affected, but as its not doing this, I believe either the fuse for ABS may have blown, or the module is the issue.

 

Start off by tracking the fuse and replacing it if necessary.



#3 GrahamV

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Posted 25 January 2014 - 08:54 AM

Thanks very much. That is very helpful.  I really hope its not the ABS module as the car is only worth a few hundred pounds and it may mean I have to lose her. She runs really nicely otherwise and has "only" done 45k miles.

on the other hand if it is the fuse, that would be a great result! Any idea which fuse it is, or is there somewhere where I can find a list of the fuses?

The price of speed sensors on the wheels looks reasonable. Is there also one on gearbox/transmission? I assume there is no way of telling which is faulty - I guess its just trial and error. I have read to test they should show about 1,000 ohm resistance

 

Many thanks for the post - Graham



#4 jeebowhite

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Posted 27 January 2014 - 12:51 PM

Hi Graham,

 

Best bet is to buy Ford branded sensors, you will end up with a world of trouble trying to use one aftermarket amongst a load of Ford!

 

As for the fuse diagrams, I dont know of a reliable source, but a quick search on google should come up trumps!

 

Ordinarily the error codes would shout "here I am" (they did on my car last year!) as I tracked down the issue to the offside front wheel, turned out to be the loom at fault... but if your not getting that, it makes it more difficult...



#5 GrahamV

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Posted 30 January 2014 - 06:44 PM

Hi

Sorry for delay in posting back but have been waiting until now to get the use of a more advanced scanner. I had loads of codes, so deleted them all, drove a hundred yards, and did a fresh scan. I got the following reading:

C1236 - Speed Wheel LR Input signal missing

C1155 - Speed Wheel sensor LF Input circuit failure

 

It seems a coincidence that both front and rear left side have both failed, or am I misunderstanding this reading? Is it possible there is a failure, bad connection where the left hand leads connect to the main unit? I am not sure where to find the main abs unit nor what it looks like!

Many thanks for help, Graham



#6 Stoney871

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Posted 31 January 2014 - 07:15 AM

The results do seem to point to a common denominator.

For both sensors to fail is unlikely.

I'd say trace the loom from both sensors and follow back where you can, checking for damage or corrosion.



#7 jeebowhite

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Posted 03 February 2014 - 03:57 PM

Sounds like the looms as Clive said.

 

I had an issue with my ABS that killed the car, the loom was the fault and the job was done for £55 no further issues since!



#8 GrahamV

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Posted 03 February 2014 - 11:06 PM

Thanks for the postings. I have been playing with the diagnostics tool. It was able to read the speed sensor speeds coming from each wheel. They were identical which I thought was encouraging.

And it seems to have cleared the error. The abs light has gone and speedo works fine. I am thinking maybe something was jammed in the teeth of speed sensor and has now cleared?

Anyway thanks for the help



#9 Stoney871

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Posted 04 February 2014 - 12:12 AM

Dirt and water can interfere with the abs sensors, hopefully your trouble won't re-occur.




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