Doors won't lock when shifter moved from Park

(Loren Engrav) #21

Still fiddling with this.
Turns out another thing is faulty. The memory buttons 1 and 2 (steering column position, etc) are to work only in Park. But they work in R and D. So now I have

  1. doors don’t lock when moved from Park and
  2. memory buttons work when in R or D and
  3. and there is a click under the J-gate when stepping on the brake when not in Park as if car saying ok to move from park
    is interesting
    will keep fiddling but not yet spend $$

do these events generate fault codes that can be read with proper equipment?

(Eric Capron) #22

It all suggests that the Not In Park signal is not reaching the Body Processor Module reliably when you move the selector out of Park (or that there is an intermittent fault in the BPM which is possible but very unlikely). The NIP signal is an input to the steering column control part of the Body Processor Module and if the BPM thinks that the transmission is still in Park when it isn’t, it will allow the column movement controls to work in D or R.
Also, I think that the click that you can hear when you press the brake is the Park release on the J Gate. Again, this suggests the BPM doesn’t know that the selector is no longer in Park.This should be inhibited once out of Park so you shouldn’t hear it once in D or R.
The only way to fix this is to try to track down whereabouts the problem occurs. It could be the switch, it could be the connector, it could be the wiring and although I doubt it very much, it could be the BPM.

If you want to fix it you will have to set up to do some tests as I suggested in a previous post.

(Grahame Loader) #23

Start with the ground, as ground faults are a common source of electrical problems.

(Eric Capron) #24

The ground concerned is a logic ground located on the left hand A post. There are two tags on the eyelet. Both have black wires with pink tracers. The NIP switch is the right hand of the pair.
The wire from the switch goes through a splice which in most cases is a nuisance but here might be helpful because one of the other wires into the splice comes from the boot release switch which, therefore, shares the same logic ground. So a quick (but not 100% certain) check is to see if the boot release still works when you have the doors not locking problem. If it does that suggests but does not prove, that the ground is OK.

(Loren Engrav) #25

thanks all
I can / will do the boot release test
is time to do the other testing but is beyond me and I have not found a local “old Jag” expert but will keep trying
thanks again

(Loren Engrav) #26


tested boot release and it works

(Eric Capron) #27

Well, that probably rules out the fault being a bad ground.


To sum it up, these cars are very susceptible to being left alone. They don’t like it.
I know because I’m bringing mine back to life after parking it for two years.
Diagrams don’t necessarily help.

(Eric Capron) #29

I agree except I do think you need to have the electrical guide. I think we should remember that early XK8s are now over 20 years old and although in some areas they were highly innovative, they also inherited much from a design that itself was 25 years old. In addition to that, they were built in a factory on an ageing line and it all shows. If you compare the construction of an XK8 with an S Type built at the same time but on a brand new line in a modern facility, they are worlds apart. The XK8 is positively crude in comparison.
Nevertheless, they can very largely be maintained by amateurs with time and patience and a few extra electronic tools but are now well beyond any economic repair if you have to pay someone else to do the work.

(Loren Engrav) #30

Still struggling with this; sorry
parts numbers
JLM203404 changed to LJA6190AC
MJA4940AE then to AF then to AG

show up at

would like to understand what each of them actually does?
do both / either control drive away door locking?
thanks again

this will end, someday

thanks again

(Eric Capron) #31

JLM203404 is a microswitch on a small bracket that fits at the forward end of the shifter mechanism. Its function is not described but from its position, it looks fairly certain that this switch operates when the lever is moved away from the P position. My guess is that this is the Not in Park switch.
MJA4940AE is a plate bearing two microswitches that operate at different positions of the shifter. It looks like one will operate when the shifter is in R, the other when in D but this thought is only derived from a picture I have seen of this plate.
As I have mentioned before, on XK8 the Drive Away Locking is not really drive away because the doors lock as soon as the shifter is moved out of Park and not when the car starts to move as is the case with some other models. The locking function takes place when a set of conditions is met, not just when the shifter is moved. Other inputs to the controller are likely to be doors closed, key in ignition, key in position II etc. so you can’t just point an accusing finger at one component and say it must be that.
In general, there are two methods of fixing faults. One is that you just change large items until the fault clears, for example, in this case you could just change the entire shifter assembly and see if the that cures it. If it doesn’t you change the module and so on. This is usually adopted by the larger dealers because it is relatively fast and the customer bears the whole cost.
The other way is sleuthing - carrying out a series of tests and interpreting the results. This is the home mechanic’s way because you end up only replacing the faulty part. And, by the way, if it turns out to be a faulty microswitch you can just replace the switch for pennies, you don’t have to by the whole plate, bracket and cable but you either have to do this yourself or find someone with the necessary skills and pay them.
Unfortunately, yours is an irritating, intermittent fault that would annoy the hell out of me but if you have to pay someone else to track it down and fix it I suspect you’ll need deep pockets. Sorry to not be able to be more help.