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Speedo Conundrum!


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#1 maq

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Posted 05 July 2019 - 09:54 AM

Hi all

 

Looking for some thoughts & advice :)

 

I'm suffering an intermittent, mostly zero reporting speedo and I wanted to sound out my thinking before ordering parts etc

 

  • Speedo shows zero most of the time, occasionally flicks up and down
  • No ABS warning light. No ABS faults on OPCOM
  • Engine is running fine, no stalls as reported on similar posts
  • OPCOM reports zero speed too when driving, hence I'm thinking its not the cluster
  • If I unplug the pax rear sensor, ABS light comes on. I expect this proves the wiring is ok.

 

Due to the above, I'm thinking the wiring is fine as the error is thrown as soon as the open circuit is detected, as is the cluster as the ECU is also reporting zero speed.

 

 

I'm thinking it has to be the sensor at fault on that basis, so new hub required.

 

Any thoughts or views on whether my reasoning makes sense? I'm planning to jack the car up next weekend and test the voltage across the sensor to see if it shows anything when the wheel is spun as a further confirmation

 

Thanks

M.

 

 



#2 martinroger

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Posted 05 July 2019 - 11:34 AM

Is the ABS ECU responding OK on Opcom? Having 0 speed on one of the wheels should trigger the ABS whenever you brake, if it is not considering a fault.
Have you considered that maybe you had a shorted sensor?

#3 ciderbooze

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Posted 05 July 2019 - 11:39 AM

Quick thing to try http://www.vx220.org...ack-dash-reset/

#4 aquilaproejct

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Posted 05 July 2019 - 12:00 PM

I had samle symptoms. It was the abs controller. Verify by making a harness and connecting passenger to drivers to check the hub.

#5 maq

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Posted 05 July 2019 - 12:06 PM

Good call on the harness idea. I'll also try the stack reset.

 

ABS unit checked out OK on opcom, no faults but then it's also not showing a fault or any light on the dash given the zero speed.

 

Will order some of those connectors and build a harness to connect to front sensor and see if it changes, great idea for little cost

 

I do see your point on the ABS controller, given its not flagging a fault.. Are they difficult to replace?



#6 aquilaproejct

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Posted 05 July 2019 - 12:31 PM

Very easy to replace. Mine was setting no codes either. Other check was I think opcom can read speed out of the engine ECU. If not tech 2 does. Mine was zero with the dodgy ecu. My car also had an occasional rough idle and stall at idle from this.

#7 maq

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Posted 05 July 2019 - 01:29 PM

I actually tried the ECU speed reading with OPCOM last night, and yep it was zero

 

Sounding like ABS ECU then. 

 

Any good tips on how to replace? Did you get new or second hand?



#8 siztenboots

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Posted 05 July 2019 - 02:38 PM

wiring loom problem between abs controller and ecu , Pin 11 on the black plug behind the expansion tank , yellow+grey wire. Check continuity back to the abs. Also check the vehicle speed signal is not damaged/grounded on the Stereo DIN plug pin 5 , also yellow/grey.

 



#9 aquilaproejct

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Posted 05 July 2019 - 09:45 PM

As siztenboots suggest check the wiring as been well.

I just got a second hand controller.
Release the lever lock harness connector
4 screws on top of the hydraulic unit.
Lift ecu straight up and replace.

#10 maq

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Posted 07 July 2019 - 12:13 PM

That sounds nice and easy. Thank you all, will check wiring first then go from there

#11 maq

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Posted 10 July 2019 - 04:41 PM

I've had the vauxhal tech diagnostics on the car today.. Seems that each wheel is reporting good speed, when the needle is zero or boucning all over the shop!

 

I've just tried a stack reset so will see if that makes any difference, but given the symptoms I'm now wondering if there is a wiring issue between the ECU and the dash?

 

Any more thoughts appreciated, will report back post reset and I'll check connections too



#12 martinroger

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Posted 10 July 2019 - 06:46 PM

Is it reading correct speeds through the OBD as well?

#13 maq

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Posted 10 July 2019 - 07:44 PM

When I checked a few nights ago, the speedo was in a misbehaving mood reporting zero and ODB through OpCom was reporting zero too.. I'm going to do another test, but I believe opcom and the speedo are in agreement and equally reporting the same thing


Edited by maq, 10 July 2019 - 07:45 PM.


#14 aquilaproejct

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Posted 10 July 2019 - 08:50 PM

Sent you a response to your pm... Abs controller can be interogated for each wheel rpm which sounds likes its ok. Then the abs module sends out a vehicle speed based on the left rear.

#15 martinroger

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Posted 10 July 2019 - 10:05 PM

It sounds to me it's either the ABS module having trouble sending the speed pulse out,or somewhere on the wire that you have something loose. Have you checked the plug at the ABS ECU level?

#16 Exmantaa

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Posted 10 July 2019 - 10:55 PM

The speed signal from the ABS module is spliced somewhere in the loom in 2 wires; 1 to the instrument cluster and 1 to the engine (through X connector)

=> Yellow / Grey wire on pin 3 from the ABS connector.

 

https://www.speedste...rake System.pdf



#17 maq

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Posted 11 July 2019 - 06:56 AM

Thank you both for the additional suggestions. Next step for me is to do the wiring checks, I've got a multimeter in-bound.

 

Any idea what readings to look for? Is it making sure it's not grounded/zero resistance?






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