Don't disconnect your XJ8 battery if you can help it.
Discussion
Cecil said:
When I went to get my battery changed, at a battery specialist, they said "oh, its one of those", "we don't recommend disconnecting the battery if at all possible, so lets use this swap out harness that keeps the car powered up" 
Aye, the sparks that came out to me today to start the diagnosis said pretty much the same thing.Rubbish really.
Both. 
This car has a full main dealer history, one previous owner who, by the stack of bills that came with the car (he kept bills for every single thing - air fresheners, tyres, pads, wiper blades...everything) doted on its every whim and yet it is still the most unreliable car I've ever had...including an E reg Seat Ibiza!
I will be going back to Mercs I think, this thing is just a phuqing joke.
This car has a full main dealer history, one previous owner who, by the stack of bills that came with the car (he kept bills for every single thing - air fresheners, tyres, pads, wiper blades...everything) doted on its every whim and yet it is still the most unreliable car I've ever had...including an E reg Seat Ibiza!
I will be going back to Mercs I think, this thing is just a phuqing joke.
BigNige said:
Both.
This car has a full main dealer history, one previous owner who, by the stack of bills that came with the car (he kept bills for every single thing - air fresheners, tyres, pads, wiper blades...everything) doted on its every whim and yet it is still the most unreliable car I've ever had...including an E reg Seat Ibiza!
I will be going back to Mercs I think, this thing is just a phuqing joke.
Well I wouldn't recommend a 2001 Merc. My Mrs' one has been a nightmare.This car has a full main dealer history, one previous owner who, by the stack of bills that came with the car (he kept bills for every single thing - air fresheners, tyres, pads, wiper blades...everything) doted on its every whim and yet it is still the most unreliable car I've ever had...including an E reg Seat Ibiza!
I will be going back to Mercs I think, this thing is just a phuqing joke.
a8hex said:
BigNige said:
Both.
This car has a full main dealer history, one previous owner who, by the stack of bills that came with the car (he kept bills for every single thing - air fresheners, tyres, pads, wiper blades...everything) doted on its every whim and yet it is still the most unreliable car I've ever had...including an E reg Seat Ibiza!
I will be going back to Mercs I think, this thing is just a phuqing joke.
Well I wouldn't recommend a 2001 Merc. My Mrs' one has been a nightmare.This car has a full main dealer history, one previous owner who, by the stack of bills that came with the car (he kept bills for every single thing - air fresheners, tyres, pads, wiper blades...everything) doted on its every whim and yet it is still the most unreliable car I've ever had...including an E reg Seat Ibiza!
I will be going back to Mercs I think, this thing is just a phuqing joke.
Our 57 reg E class has been a model of reliability as has our Viano.
Nuts to it, I might just by a bloody Ford Fiesta.
It the key is out of the ignition when you disconnected the battery there shouldnt be any danger of causing damage. If the ignition is on when the battery is disconnected there is a high probability of damaging one or more modules on the car.
Some X308's are 12 years old now, they are going to be troublesome, but thats the price you pay for having a jag. All the premium brands, Jag Merc BMW Audi etc have similar levels of electronics. Very compliacated and difficult to diagnose some faults. Thats just how it is unfortunatly.
Just for an example lets look at somthing as simple as the headlights. Not that long ago, you turn on your headlights, a low power wire from the switch trips a relay and a high power is connected to the headlamp bulb, simple.
Now a control module looks for a signal from the headlight switch, if the signal meets the required value the module (dash for example) sends out a message on the network to the module that controls the headlight (BPM or FEM for example) the BPM/FEM then sends out an earth to pull in a relay and turn on the lights, at the same time the originaol signal on the network saying the lights are switch on, is picked up by other modules, so your nav screen changes to night setting the dash and back lights come on and your electro-choratic mirror is switched on etc.
SO before if the lights didnt work it was the bulb the switch or the relay. Now it could be the switch, the module thats wired to the switch (usually dash) or the output-state module (£500 of FEM or Body Procesor) the network being down, the relay, the bulb or any of the wiring inbetween.
Having been factory trained for 7 years on X308 and X350 I trust mobile auto electricians about as far as I can spit. Unless they changed the set of brown 5 pin relays, that might not have fixed the fault. Or a simple "Hard reset" disconnect wait for a minute and reconnect may have fixed it for free.
Some X308's are 12 years old now, they are going to be troublesome, but thats the price you pay for having a jag. All the premium brands, Jag Merc BMW Audi etc have similar levels of electronics. Very compliacated and difficult to diagnose some faults. Thats just how it is unfortunatly.
Just for an example lets look at somthing as simple as the headlights. Not that long ago, you turn on your headlights, a low power wire from the switch trips a relay and a high power is connected to the headlamp bulb, simple.
Now a control module looks for a signal from the headlight switch, if the signal meets the required value the module (dash for example) sends out a message on the network to the module that controls the headlight (BPM or FEM for example) the BPM/FEM then sends out an earth to pull in a relay and turn on the lights, at the same time the originaol signal on the network saying the lights are switch on, is picked up by other modules, so your nav screen changes to night setting the dash and back lights come on and your electro-choratic mirror is switched on etc.
SO before if the lights didnt work it was the bulb the switch or the relay. Now it could be the switch, the module thats wired to the switch (usually dash) or the output-state module (£500 of FEM or Body Procesor) the network being down, the relay, the bulb or any of the wiring inbetween.
Having been factory trained for 7 years on X308 and X350 I trust mobile auto electricians about as far as I can spit. Unless they changed the set of brown 5 pin relays, that might not have fixed the fault. Or a simple "Hard reset" disconnect wait for a minute and reconnect may have fixed it for free.
To be fair, the guy seemed to know what he was doing and his way around Jags.
Found the faulty circuit/network/wossname as the heated screen which was pulling 4amps, took the fuse out and it was down to about 0.6 which he reckoned was still a bit high.
So, going in on Tuesday for a full diag but if push comes to shove, I can live without a heated screen.
Found the faulty circuit/network/wossname as the heated screen which was pulling 4amps, took the fuse out and it was down to about 0.6 which he reckoned was still a bit high.
So, going in on Tuesday for a full diag but if push comes to shove, I can live without a heated screen.
Sorry its a main dealer tech thing to dis-trust everyone else, most of the cars we get other people have worked on are clearly bodged. That said, does sound like your chap has found it, and in the correct logical manner.
I've had somthing very similar on XK but not XJ before. Masice battery drain (5amps or so) Found to be Water in the heated screen relay base, shorts across effectivly putting the heated screen on even when its all off (nothing to do with disconnecting the battery), Water gets into the heated screen connectors under the scutle trim, capilary action sends it along until the lowest point is the heated screen relay base.
Took me a while to find it, hot screen on one side first thing in the morning was the urika moment.
I've had somthing very similar on XK but not XJ before. Masice battery drain (5amps or so) Found to be Water in the heated screen relay base, shorts across effectivly putting the heated screen on even when its all off (nothing to do with disconnecting the battery), Water gets into the heated screen connectors under the scutle trim, capilary action sends it along until the lowest point is the heated screen relay base.
Took me a while to find it, hot screen on one side first thing in the morning was the urika moment.
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