ECU unable to be read for faults

[davewbarrick756]

Hello!
I am looking for any help for my Big Beautiful Cat!
It’s a 2008 Sovereign V6 diesel with a restricted performance light on the dashboard.
My local garage had it for an hour unable to read the fault with their OBD machine they tried 3 of them !! No joy, found this tech wizard who likes to problem solve !! Sat with him for an hour, he came up with one of the pins in the connector under the steering wheel not going to Earth.
He went off, we waited patently !!
We went off to Scotland week later, dashboard light came back on around 15 miles from home !!
Well he said don’t worry if it comes back on carry on driving! So we did, I worried a wee bit but carried on! Got up to Scotland, had a good evening meal went to bed, woke to a fantastic breakfast jumped in the car for a trip out, no message!!
Enjoyed holiday, came home, drove around, waited for this guy to get back to us!
He did, after the message came back on 3 weeks later!
Anyway told us he’d spoke to someone at Jaguar and they said it’s the ECU replace it,
Now I’ve got one but very loathed to replace it for the one in the car has no symptoms of a failed or even failing ECU.
No check engine light on
No engine stopping for no reason
No car shakes
No loss of fuel efficiency
The only thing it fails on is extra speed when trying to overtake
It drives well at 30, 50, even 70 down the motorway!!
Except when I want that extra power to overtake !! Not there!

Has anyone ever had this problem of not being able to read the computer?
Oh and the only thing that’s got worse is the fact that this message now appears moments after starting to drive than 10 to 15 miles of driving
Has anyone any ideas or come across this problem so we can enjoy our Beautiful Big Cat without any lights on the dash !!
Regards Suzie

[PaulGover]

Bad luck!

I have a similar car, with a similar set of symptoms, though not quite as bad. The problem is probably with your local (non-Jaguar?) garage's ODB reader. As far as I know, there are a lot of cheap readers that use one of two chips to do the hard work, and the majority use the older chip because it's cheaper. As that chip doesn't understand the latest car communication networks it use an older and slower protocol. The net result is you have to wait a long time (30 minutes, an hour or more) for it to get through all the stages to retrieve all the messages, instead of a few seconds. Alternatively, there's a bad connection or failed ECU. It might be worth getting your garage to try unplugging and replugging all the relevant ECU connectors, that can remove surface corrosion and restore a bad connection.

If you have not already done so, I recommend a trip to a Jaguar dealer, and shell out £50-£100 for them to plug their manufacturer-supplied ODB reader in. It should have more success... If not, you are in a bit of a bind - no garage will be able to diagnose the fault, and probably the car will fail its next MOT if the light comes on, so you will have to replace the faulty ECU to get the ODB message.

As to intermittent Restricted Performance lights, two common causes are (1) a failure of the rear RH wheel speed sensor, part of the ABS system; when it fails, the ECU gets very confused trying to work out how the engine is still turning, the car's doing say 30 mph, but one wheel's stuck! (2) damage to the electrical wiring on the Exhaust Gas Recirculation valve circuit - at least, that's what I have - it shows up in wet weather when spray reaches the engine bay and causes a short in the circuit. But there are literally hundreds of other faults that can cause Restricted Performance, so the only way to know apart from replacing every component on the car is to get that ODB error code!

[davewbarrick756]

Thanks Paul
I shall take all that on board I think I’ll have a go at the main dealership see if they can read it at least I’ll give it a try before changing the ECU unit !!
There is a whirring noise that is coming from the front which could be what you say ! It’s in for a service next week so I’ll get them to have a look !!
Suzie

[ptjs1]

Suzie,

Don't even think about the expense of changing the ecu just yet! I can't believe it's the ecu at fault. It's far more likely to be wiring problem on the OBDII plug (I had an x308 with a similar problem where one of the wires was chafed through) or else at the ecu connection, or else an earth problem on the car (the earth points behind the headlights are notorious for corrosion).

Good luck

Paul

[davewbarrick756]

Hi ptjs1 Paul
We have got pesky blinking headlights too and I was told about one of the connections in the reader port not going to earth !!
And I just remembered the cruise control won’t engage while this light is on the dashboard
I got it in for a service on Thursday at Sheffield choose him from reading an article in the jag mag !!
I don’t want to change the ecu call it a gut feeling but I don’t think it failing at all my car runs too well for it to be problematic
I shall keep searching to find a solution
Suzie

[andypryce]

I bet it’s the earth point behind the headlight, notorious for failing