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Registered
1999 4.6 P38 HSE
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2 Posts
Discussion Starter #1
Hi all, I have seen some previous threads talking about the P38 speedo not working but can’t quite find something applicable to my issue but I apologise if this has already been covered.

My ‘99 P38 speedo has stopped working. I have checked the relays with a multimeter and all are good (suspected ABS control unit failure).
All other instruments in the cluster are working fine - fuel gauge, temp, rev counter and all alert lights. The equipped speed warning is working and sounds at the set speed which leads me to think that the car is still registering speed fine just not displaying it.

Has anyone else had this issue or able to help? Hoping that it is just wiring behind the dash?
Thanks in advance. James
 

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Registered
1995-2002 Range Rover P38A
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1,439 Posts
The speedo gets its signal from the ABS sensors via the ABS ECU.
A '99 MY should have the later black coloured Wabco ECU, type D. They do occasionally fail.
 

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Registered
1999 4.6 P38 HSE
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2 Posts
Discussion Starter #3
Thanks Dave,
I get that the speedo gets signal from the ABS ECU and the sensors can be at fault but am wondering as the car seems to be registering speed and just not displaying if this may not be the case? Thanks for your help
 

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LEGACY VENDOR
1995-2002 Range Rover P38A
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4,220 Posts
The Wabco D Ecu's do have some habit of failing - but the only fault I have found with them (and am able to fix most of the time) is a persistent "LH Rear Sensor Short to Another Sensor" fault.

If the vehicle is registering speed in other ways - IE in the speed warning, or if the EAS still moves automatically between normal and highway height and back again when you go above/below 50mph/80kph then that to me says that the ABS ECU is working as it should do.

The speedo signal is sent on a separate wire from the BECM to the instrument cluster, rather than over the serial link (Though I would have expected the cluster to use this aswell for the speed limit warning)... but it's worth checking the integrity of that wire... The signal comes out of the BECM on pin 16 of the 16 way White connector, which is one of the 3 underneath the fuse box on the side of the BECM. (the side you look at from the RHF Door. It's a yellow wire, and runs up to the connector at the instrument cluster, and it ends up on pin 9 of that connector.

I'd give that a check for continuity first. If that checks out, then it could be an issue in the cluster itself, or a fault on the speedo gauge. IF that's the case then there are a few ways to go about investigating that, without messing up the mileage of the vehicle by just plugging in another cluster. Though, it is pretty rare for the cluster PCB or the gauges in fact to fail.

Let us know how you get on...

Marty
 
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