[steve yeates]

Have had an absolute nightmare of a fault in my 2003 3.6 x350. On start up one morning I got the engine systems failure with abs and dsc unavailable messages on dash. My friend who has an identical car had this problem before so we knew the messages typically point to throttle position sensor failure. We changed this no joy! Then we started substituting parts from his car starting with throttle body then pedal then we started pining out cables suspecting a corrosion or chaffing issue no joy. Have now had 2 auto electricians spend around 8 hours each both suspected ECU. Had a ecu cloned from my unit however when this was installed we had multiple additional faults. I have now sent ECU back and requested my original back. I have noticed that the throttle relay is not pulling in and cannot seem to get info on what can hold this relay off.
To recap
1 throttle body changed with known good unit & also brand new Jaguar unit
2 throttle pedal exchanged with known good unit
3 fuse box changed with known good unit
4 wiring pin and load tested to throttle body and pedal
5 awaiting ECU company to get my ECU back to me.

have had the car for several years battery is good 3 months old car is dry stored and only about 3000mls per year

 

[JimC64]

Welcome aboard Steve

Sorry to hear of your issues, likely one of the 350 guys will be able to help

Jim

 

[JimboV8]

Welcome to the forum, enjoy. The first thing to check is the ground points behind the headlights.

 

[JimboV8]

Take a look here for all the information you need; SILENTUM SICARIUS - My Super V8

 

[MrKis]

+1 on the ground points.
The throttle body’s and ECU’s are rarely troublesome on the 4.2 /3.6 v8.

 

[steve yeates]

Thanks for all the responses so far guys. I neglected to mention that one of my first checks was indeed the ground points. I have owned this car for about eight years and have had the Christmas tree on a few occasions. I will replace the studs with stainless nuts and bolts over the next couple of days but I am convinced the aluminium studs are ok and I have cleaned them of any corrosion.

I should get my original ecu back tomorrow and I plan on spending a couple of hours on it tomorrow evening should the missus allow it😀.

 

[MrKis]

The studs corrode on the inside, so look ok but if you try tightening them a bit for example, they’ll snap because they are bad.

 

[ALUCAN]

The studs corrode on the inside, so look ok but if you try tightening them a bit for example, they’ll snap because they are bad.

+1 for the corroded studs.

Zinc plated bolts are better than stainless to avoid electrolytic corrosion of the body, but I went further and used sacrificial aluminium washers.

 

[steve yeates]

Hi guys

Took the general advice of redoing the earthing studs used stainless 8mm nuts, bolts, serrated washers and thoroughly stripped back to aluminium around new studs. Sorry to say it didn’t work. I’m convinced the ECU is getting told by some other module not to give throttle and stay in limp mode.

when I got my old ECU back in there were several fault codes mostly relating to rear BCM, rear wheel sensors,sunroof(none fitted), heated seats, invalid engine speed at electronic parking brake, fuel pump out of range.

all the above have cleared and still no throttle response. In fact only sunroof fault now on car.

can see the throttle pedal on live data, can also see tps on live data, all voltages look ok if compared to Jaguar wiring diagrams on jag repair.com . If I unplug tps throttle motor moves looking for feedback. Again pointing to ecu being held in limp mode.

Again any help much appreciated I do love this car.

Steve

 

[Spacemonkey]

Has the car been jump started? My software issues arose after jumpstarting my TT and getting the polarity wrong for a split second while the Jag was running. Screwed the software and possibly various modules/ECU. As you only do 3k a year I can imagine the battery could suffer unless on trickle?

 

[ALUCAN]

Hi guys

Took the general advice of redoing the earthing studs used stainless 8mm nuts, bolts, serrated washers and thoroughly stripped back to aluminium around new studs. Sorry to say it didn’t work. I’m convinced the ECU is getting told by some other module not to give throttle and stay in limp mode.

when I got my old ECU back in there were several fault codes mostly relating to rear BCM, rear wheel sensors,sunroof(none fitted), heated seats, invalid engine speed at electronic parking brake, fuel pump out of range.

all the above have cleared and still no throttle response. In fact only sunroof fault now on car.

can see the throttle pedal on live data, can also see tps on live data, all voltages look ok if compared to Jaguar wiring diagrams on jag repair.com . If I unplug tps throttle motor moves looking for feedback. Again pointing to ecu being held in limp mode.

Again any help much appreciated I do love this car.

Steve

If your car is reporting faults where the item is not fitted, then it would be worthwhile checking the car configuration and dealer options. If the ECM is in conflict with other modules, especially the instrument pack which manages the network, then you get the situation that you are in. You may be faced with reconfiguring affected modules.

A fundamental check is voltage loss under electrical load i.e at the front of the car, not at the battery terminals. You really need a fully charged battery to be maintained. Repeated or long SDD sessions can reduce the voltage below what is needed to write to the modules (more volts needed to write than to read). Let us know what you find and we can collectively apply our experience.

 

[MrKis]

Which earth studs did you do?

 

[steve yeates]

Hi Guys

I replaced the three studs behind headlights, I haven’t had to jump the car as I use a maintenance charger, the battery is reasonably new(under 6 months)Bosch. Car did have a 30 mile run the day before this happened. Whenever I’m doing any long diagnostics I have a snap on battery backer designed for diagnostics. I haven’t monitored the voltage on the front end of car and I will give it a try but haven’t noticed any thing that would lead me to think of volt drop on front end. Costs nothing to check.
Thanks again guys
Steve

 

[JimboV8]

May also be worth checking the connector for the ECU especially the pins and the plug for signs of corrosion. This is the one below the pollen filter in the engine bay.

 

[steve yeates]

Hi Mate
Yes I have done that also, I have had the ECU out and sent away for cloning. ECU company did make a hash of it and sent me an ECU with more faults on it than I could count. So back with my original I’m now trying to find a company that can test my original in the mean time back to more diagnostics. I’m now thinking ABS module??

 

[JimboV8]

Give these guys a call; JAGUAR Product Catalogue

 

[steve yeates]

Hi Jimbo v8

I did give these guys a call they cannot test the ECU for definite they have offered to take it in to their development department and try to test it “5 day turn around” if they cannot test it they will return it no charge. Which is very good but I will then loose the ability to carry on checking the rest of car. Until the ECU is back in my grubby hands. And I’ve just got it back after a lost 10 days with last ECU company.

steve

 

[MrKis]

Are there more engine bay earth studs you could check? Or are the three new the headlights the only ones in play?

 

[steve yeates]

I have checked and cleaned the earths at the ECU just in front of pollen filter if you look in to the earth studs there is actually about 30 in total around the car i honestly do get why your thinking earthing but looking at the wiring diagram the common studs are pretty much covered by the ones at headlights

 

[MrKis]

I have checked and cleaned the earths at the ECU just in front of pollen filter if you look in to the earth studs there is actually about 30 in total around the car i honestly do get why your thinking earthing but looking at the wiring diagram the common studs are pretty much covered by the ones at headlights

Ok, worth mentioning the simple stuff just in case.