Hi Folks,

So, as the title mentions, I have an intermittant dead electrical system issues. It never happens when driving, it happens after I turn off the car. The entire system is dead...no interior lights, no instruments, no horn, no central locking,etc. It acts like the car has the battery disconnected.

The problem isn't preceded by any common event..sometimes I can tell it's happened right as I turn off the car, sometimes I don't notice until I open the door and am greeted by, well, nothing. There is a real loss of power as the trip computer resets to zeros.

There is an issue with the drivers door. The central locking system doesn't always lock the door, although it does set the alarm. The time before last power was restored by slamming the drivers door...done in angst, not by design...but that doesn't always fix it. The last time, I was rooting around in the trunk and the power came back on.

So, any ideas where to start looking? I have a parts car and could switch out the door lock on the drivers door quickly enough (well maybe...chuckle) and I know that locks/unlocks with the system and the key.

Thanks in advance,

 

The general consensus is the Negative Battery cable is bad (bad ground). Don't buy another battery (I bought TOO many to count before finally figuring out the problem on my own). Switch out the negative battery cable ($104 at the Jaguar dealership). Problem solved.

 

Could it be that simple? That's terrific!

Thanks very much...I'll get on one order immediately!

 

I could be that simple, but before buying that expensive cable try connecting a jumper cable from the negative terminal to a grounded bolt in the trunk.

 

+1. Also try cleaning the ground point terminals and make sure they are tight.

Preventative maintenance is better than reactive maintenance.

 

It does sound like battery connection issue. It is possible that connection is lost while driving as well, but things stay powered from generator when it happens so there is a little effect.

First thing I would do is inspect both connectors and cables coming from the battery to that connector in the trunk, and them from that connector further . Positive cable is not immune from the failure.

It could also be loose connection between "jars" in the battery, rare but possible. Check if there are any cracks on the battery case.

 

Thanks, all. I'll try a jumper first...

Remarkably, I had the same issue with my X300 back in 2004 but traded it before I ever found out what it was.

What surprises me is that it is instant on and off. There isn't any graying out, the starter spins the engine over as per normal....when it isn't blacked out. To be honest, it almost seems like a thermal circuit breaker....

Take care,

 

The electricity does not know whether the battery positive or negative cable has resistance, so I ain't buying the negative cable analysis for a minute. Look up Kirchoff's current law. That said, the same guy has a voltage law that says the algebraic sum of the voltage around any path is zero. So , start with a positive 12 volts at the battery and use a voltmeter to find out where it is dropping before it get to the consumer of electricity. It really ain't that difficult.

 

Thinking of components known to develop intermittent faults that can block battery power to the entire vehicle, the Ignition Switch would seem to be a primary suspect. This is the actual electrical portion that mounts on the end of the key barrell. The switch can be tested for proper operation with an ohmmeter. The Electrical Guide shows which wires should connect to each other in each key position. The switch operates by connecting various combinations of three circuits to Signal Ground, so it would also be worth checking the integrity of its ground point at the EMS ground on the EMS bulkhead ground stud.

Can you provide a little more information about this behavior? Do you mean that when the no-start condition has occurred, and the ability to start returns, the trip computer has reset all its data to zeros and the engine runs with less power?

Don

 

Follow the Electrical link in my signature, it may help you out.

 

avt007 you sir are a genius! I really like your troubleshooting guide. You have a gift of making something difficult to understand simple.

 

Don,

The behaviour is that electrical system goes completely dead..as if the battery were disconnected...and when it returns on its' own the trip computer is reset to all zeros. The engine and all systems work perfectly normal with no loss of power or poor idling characteristics. It's quite odd that it all just recovers and operates normally....

 

Thanks, I will....

Take care,

 

Bruce,

Rob will know better than I, but to me your symptom sounds like an intermittent loss of battery power between the battery and the ignition-powered components. Places I would check first would be the fuses and connector posts in the high power protection module, and the battery power connections at the fuse boxes, which are daisychained together in this order from the battery and power protection module forward: RH Heelboard Fusebox, LF Heelboardbox, Engine Management Fusebox, Engine Compartment Fusebox.

I may be wrong in thinking that a loss of power to the Body Processor Module could cause your symptoms, but the BPM receives power from fuses 5 and 7 in the LH Heelboard Fusebox, so the battery power connections at least to that point might be worth checking, as well as the electrical connector at the BPM and its ground.

Cheers,

Don

 

Thanks! I always appreciate feedback. I ended up going into technical training as a career, and I love it.

 

Bruce, from your description, I'd suspect problems in the trunk area, specifically the power module with the big fuses. The loss of everything can really only happen in the trunk. The famous engine ground strap only affects the engine and charging/starting.
The ignition switch can't cause these symptoms, either. It's got to be within a couple feet of the battery, I'd say, or possibly the RH heelboard, if that cable was completely loose or something.

 

Thanks. It was an assumption of mine as well but with all the power junctions I started to doubt myself. I'll focus on the trunk area and see what I can find. I'd love to be able to cause the fault....

Thanks again...

 

So the intermittant problem was happening with a greater frequency and was accompanied by new weird symptoms. Symptoms like the radio momentarily turning off when hitting the brakes. This problems always resolved when doing a hard reset...

So, thinking about when it happens, I decided to replace the battery. The old battery, aged about one year according to the previous owner, was bulged out in areas. Putting in a new battery seems to have addressed every issue and the car runs as it should...

If I don't have a recurrence of the problem over the next month, I'll call this one solved...