Speedometer Suddenly Cut Out at the worst possible moment!
 

Try not to laugh!

This Afternoon was really nice and so I thought I'd take 'Cherry Blossom' my Red XJS just out for a little drive and top up with some Petrol.

This was on a Dual Carriageway and I know this road like the back of my hand and all of the quirks that go with it.

Although its a 70mph, I wasn't in a hurry and was purrring along at 60mph but I was well aware of what was ahead.

Which was a number of Traffic Cones, which were parked on the Concrete Strip in the middle of the Dual Carriageway (which were not on the actual road itself)

There was also a Sign that said Roadworks with a 50mph Speed Limit for Safety Reasons.

But apart from the Cones, there was no sign of any Roadworks having taken place and no Workers of any description anywhere to be seen.

Its been like that for Months, with just the Cones and nothing going on.

Consequently everyone is tired of seeing this and no longer take any notice of this 50mph Speed Limit.

And just continue their journey at 70mph+

Except that is for me, because being perceptive, I had a very strong feeling that since this had lulled motorists into a false sense of Security.

One day they would put a Speed Trap there and then catch hundreds of motorists all at once.

I wasn't in a hurry anyway, as just passed this Roadworks aka a line of abandoned Cones, I was about to turn off onto the Slip Road, which is 60mph because it's a Slip Road.

So when I see the Sign for the Roadworks (abandoned cones) coming into View, I just let the Car slow down, so by the time I get there, I'm only doing 50mph.

Which I've got down to a very Fine Art, as this line of Abandoned Cones has been there for Months.

Where because I stick to the Speed Limit, it annoys the hell out of everyone else, simply because in their own heads, this 50mph Speed Limit seems to no longer exist.

Simply because those abandoned Cones have been there for ever and a day.

So Purring along at 60mph, I could see the Roadworks (abandoned cones) just coming into view, so I did what I always do and just let the Car slow down,

so I'm just doing 50mph by the time we get to the 50mph Speed Limit part.

And just to be sure I always Check the Speedometer.

At which point Two things happened both at the same time!

As I looked down at the Speedometer the indication needle suddenly dropped to Zero and Stopped Working!

Then as I looked up the next thing I saw was a 'Speed Trap' Van, on the Verge right in Front of me.

I'm 99.999999% sure that I was doing 50mph but since the Speedometer suddenly Stopped, its not what anyone would call an ideal situation.

Because I always stick to the limit and don't Speed.

How do I get to the Sensor to see what went wrong, do I have to remove the 'glove box' or the whole center Console?

I see that someone else has the same problem.

OB,

There are four components in the chain:

- The shimmed speedo sensor mounted in the back of the rear diff at the top. This sends a signal to the:

- The speedo interface module which is mounted in the boot. This then sends a signal to both:

- the trip computer &
- the speedo

So, the first thing to check is whether your trip computer is reading the distance. If so, it implies the first two components are working correctly.

Then you check if the speedo is reading distance via the odometer or if both the speedo needle and odometer are at fault. If both at fault, it implies the speedo is faulty BUT

I have recently seen a situation where everything worked correctly except the speedo, but the speedo then worked when put in another car. It transpires that (on facelift cars at least) the speedo needs a more robust voltage than the trip computer to work. So it can be a wiring integrity or earth to the speedo itself that is at fault.

So it's out with the multimeter and start working back from the speedo.

Good luck

Paul

I have the same problem and I know my sensor is bad ..... the problem is I can't find the sensor "DBC11116" discontinued. So I guess I got to wait for someone to wreck their Jaguar. So option B is now in play: I am now leaning towards a conversion GPS signal converted so my speedometer can read it. Maybe someone went down this road before who can shed some light on this.

Hi Paul

The Speedo has only ever dropped once but then it picked up again, so this could be a bit of a Nightmare to fault find.

I've also looked in the Boot/Trunk but don't know what the Speedo Module looks like.

Maybe you would be able to identify it from this Photo?

And then if I removed it and gave it a Squirt of Electric Contact Cleaner it might be ok?

On the other hand if its the Sensor, then this looks the job from hell, as you cannot get your hand in there to undo it.

Unless you remove the rear exhaust, or else take the bottom plate off the Cage.

Is the Sensor held in place by Star Keys, I've had a look but its hard to tell.

https://cimg0.ibsrv.net/gimg/www.jag...b7d3e130fa.jpg

https://cimg4.ibsrv.net/gimg/www.jag...7edcc025fb.jpg

Is this 'Black Box' The Speedo Interface Module?

https://cimg6.ibsrv.net/gimg/www.jag...4459718e67.jpg

Do any of these Fuses have anything to do with the Speedo?

This Fuse Panel is underneath the Kneepad underneath the Steering Wheel (UK Car)

OB,

Not sure from your pics. It's a small black box with two sets of wires coming out, one with a black plug on the end, one with a blue plug. See here:

https://www.jaguarclassicparts.com/uk/part/DAC4591

If you do a search on ebay for XJS speedo interface, you'll find lots.

If it's a very intermittent fault, can you check if the trip computer distance recording drops out at the same time? If not, it's probably the speedo or speedo wiring connections. As we all know, intermittent faults are the most annoying!

Cheers

Paul

Hi Paul

Cheers!

I'll have another look Tomorrow in daylight.

And will also Check the Trip Computer, which I never have Switched on.

If I were to have it on would I be able to see it clock up the Mileage on the fly, or do you have to take that reading after you've finished your journey?

OB,

The distance on the trip computer accumulates and changes real-time.

Paul

The speed interface unit is above the ABS ECM and has Speed Interface printed on it. Those do look like the connectors.

It has 2 outputs 1 for the speedo/cruise comntrol and a separate one for the TC, just because the TC is incrementing distance does not mean the Interface unit is working. I killed mine when doing my Cruise Control install, it has a zener diode on each output to protect the counters in the electronics, shorting the output to ground will usually take out the diode.

If your CC works and speedo does not then the Interface unit is GOOD.

BTW the first thing I would do is clean all the connectors.

Hi Warrjon

Cheers!

I've never used the Cruise Control, ever since I've had the Car, so I'll give that a try Tomorrow and then report back.

And I will clean the Connectors.

Just had a thought!

Could it be dust on the Sensor on the back of the Speedo?

I've never seen the back of the Speedo, is it some sort of magic eye like the remote control on a TV?

Would it be a good or bad idea to blast some Compressed Air from an Airline up around that Area?

Could dust be enough to prevent the Sensor on the back of the Speedo from picking up a Signal?

As the fault is intermittent, conventional fault finding sounds like an almost impossible task to achieve.

NO DO NOT blow it with high pressure. Low pressure is ok.

If it's intermittent I would suspect bad connections, 99% of all the intermittent faults I have repaired (in electronics) have been bad connections, either connectors or bad solder joints on the PCB.

This is what I would look for............

- PCB trace (on the instrument cluster) damaged.
- Connection from instrument PCB to Speedo.
- Connector from harness that plugs into instrument PCB.
- Broken wire .
- Wire almost disconnected from pin in plug.
- Corrosion or other foreign matter in connectors.

Hi Warrjon

Cheers!

Does the Speedo actually make Contact with the PCB board or is it in the form of a 'Magic eye'

If it does make actual Contact with the PCB board, would it be ok to spray the board, where it connects to the Speedo with Electrical Contact Cleaner.

Or is there a better way?

How do I get the Speedo out to take a look.

OB
The instrument binnacle has to be removed. The Great Palm's book explains the procedure clearly, and there is loads of stuff on here. The instrument pack has a blue flexible "PCB" that has TWO large multiplugs going into the back of it. These are not easy to get at or replace, but it can be done. Best to remove the steering wheel first before removing the binnacle.
The actual speedo has small bolted connections to the flexible PCB. I doubt the actual speedo is the problem, far more likely, as Warrjon said, the PCB or the connections to it. The copper tracks on the PCB are very delicate and can easily become broken or dislodged where, (eg) the multiplugs plug in. Attached pic shows the back of the binnacle and the rectangular holes where the multiplugs go in, and the other the multiplugs in the dash. The MUST go back the same way they came out. The difficulty is that there is not much loom length to allow easy replacement.


Greg

Hi Greg

Cheers!

Looks like a Fun Job, I'll have a look at Palms book like you said.

OB,

Popping the instrument cluster is much easier than it might seem. It's really a 5-minute job, I assure you. As alluded to by others, I suspect you've just got a slight connection or earth problem on the speedo. The speedo head needs slightly more voltage than the trip computer.

Having said all that, I'd still be checking the interface module connections first. Then I'd wait to see if the trip / cruise works when the speedo drops out. Only then would I start pulling the instrument cluster.

Good luck

Paul

It is getting it back in, with the multiplugs correctly seated and not having pushed the copper contacts out of line, that I find hard, Paul! Maybe my car is a bit shorter in loom length to the plugs than most?
Greg

Oh me, no speedo? Not a big deal. Just peek at the tach.


Carl

Hi Paul

That sounds like good advice but do I have to take the Wheel off?

Hi Carl

The Tach works fine and although I used it as a guide, the Speed limits are constantly changing, along the Country Roads where we go tripping.

So I'd rather have the Speedo working properly.

OB,

Just move the wheel as far down or as far out as you can. I think you've just got the reach adjustment on CB(?) so adjust the wheel towards the seat.

To take Greg's point, perhaps the looms are a bit tighter on pre-facelifts, but slim hands also definitely help! On a facelift, it helps to tip the cluster forward from the top and then reach in to carefully disconnect the plugs. I suspect the same principle applies on earlier cars.

Paul