I just read here: Dan McGrath - XJ12 Gearbox Starting Problem

That my starting problem is reasonably common and is usually in the switch part number DBC12395.

Will find a replacement part somewhere.

Bob

 

Try this. Part #1 is the rotary switch but it does look as though you do not have a rotary switch on your model.



The part number for the linear switch I gave you, DBC12395 is correct, you will have to hunt around for a used I'm afraid as they are NLA.

Also, if you do replace it, you might want to look at this tool for correctly positioning it. Auto Gearbox Linear Switch Setting Gauge - Gearbox Tools - XJ40 You can also bypass the system,which appears to be what the bloke with XJ12 did.

Is there a reason that you think the switch is the problem? It seemed like the relay was an issue? Also, when you turn on the ignition, do you see the P (Park) illuminated on the instrument panel? If you do, I doubt the switch is your problem. (But you never know on Jags )

Cheers,

Allan

 

Hi Allan

I don't know where the problem is but I've found further references to the same problem in other XJ40s.

I have the box DBC 10008 on order via EBay from the USA but it hasn't arrived yet. I will let you know if it fixes the problem.

I am trying to find the box DBC12395 but none advertised in Australia or on EBay. I'm now calling around Jag car wreckers to see if I can find one.

If necessary I'll keep changing boxes until I find the culprit!

Thanks for your help.

Bob

 

I'm getting very frustrated.......

I replaced both boxes DBC12395 and DBC10008 and checked the ignition switch and still the only way to start the car is to depress the solenoid (see above).

Can someone tell me - is there an immobiliser somewhere in the car? It is not showing in any of the circuit diagrams.

The only other possibility I can think of would be a bad earth/ground???

Bob

 

Bob,

Sorry about your frustrations

In one of your early posts, you mentioned that you had removed an after market alarm system from the car. Does the car still have the factory alarm installed? You can check by looking for the security ECU which should be located on the left rear wheel arch behind the trim. I do not see a separate immobilizer in any parts lists. There were a number of different security ECU's installed, the part numbers should start with DPP1058xx or DPP1060xx. There may also be a security switch that is in the center console armrest, perhaps you could try turning it off but I'm not sure that will have an effect?

The security ECU talks to the central processor via a serial link and the central processor send the inhibit signal to the solenoid. I think the only way to check that communication is if a local garage has an old JDS diagnostic system?

The ECU output to the solenoid should be on pin 47 of the yellow ECU connector. It should change state from ground (inactive) to 5v (active)

I'm not quite sure if you have actually tried to trace the circuit, apologies if you have but again I think the only way to find this problem without chasing your tail or throwing parts at it, is to methodically trace the circuit from the starter solenoid back to the ignition switch. That will isolate the problem.

Cheers,

Allan

 

Thanks Allan, I really appreciate your help.

I can still start the car by manually pressing solenoid 4 inside DBC10008, which eliminates any starter or starter solenoid problem. The ignition key switch appears to be OK. There is power on two wires into DBC10008 when the ignition key is on, but no change when the key is placed into the start position.

I've tried to trace the circuit, no simple task.........

Let me go check on these two points:

I don't appear to have that switch. Where is it located?

Bob

 

Bob the security switch, if fitted, should be in the center armrest. Open the lid and you should see a switch like this near the catch in front.

Amazon.com: Switch control panel button DBC12022 Jaguar XJ40 XJ6 with pigtail

In regard to tracing, you could start by back probing pin 47 of the main ECU yellow connector. You should have 12v when the ignition is in position II (ignition on) and then the signal should go to ground when you turn the to position III (engine start). Doing this first will eliminate the security system angle if the above is true.

If not then the problem lies before the ECU or in the ECU connections/grounds.

Cheers,

Allan

 

Allan

Maybe this helps:

1. There is nothing, no 12 volts on pin 47 (red wire) of the main ECU yellow connector, regardless of the ignition key position - position II "on" or position III "start".

2. There is no isolation switch in the centre arm rest glove box:





3. This plug is in front of the glove box and may be there for the isolation switch if it were fitted?



4. There is another Yellow start solenoid up behind the passenger side glove box (remember this is a right hand drive car). Will need to remove the glove box tomorrow to get to it.

5. There is what may be the security ECU, located on the left rear wheel arch behind the trim, near the gas lid opening. Will remove the trim tomorrow to get part numbers.

Any of that make any sense?

My old mechanic mate suggests it may be quicker for me to send you an airline ticket to Australia!

Bob

 

Bob,

Heh heh, I'd love to make a trip back to Oz. I lived in Perth (Freemantle) for a bit way back when and loved it. I would really love to do a wine tour of the Margaret river area.

Yes it sort of makes sense but also creates more questions than answers

You did say your car was a MY93 right? I have been basing my posts on the wiring diagrams for the MY93 and MY94 cars. Your mention of an additional relay and the fact that you had no output of any kind on pin 47, made me start to question that thought process. I have just looked at the wiring diagrams for the MY88 to MY92 cars and they are different, natch!!!

On these cars the ECU does not control the starter logic which would explain the no output on pin 47. Also there was an ignition relay in addition to the starter relay in these cars. The relay is behind the dash as you say. One diagram says it is a yellow relay and another says light blue kind. The good news is that either are used in various places on the car so you could quickly swap it for a known good one and see if that sorts the problem. These relays are known to cause problems because they are not sealed. Jaguar issued a TSB about them in the mid 90's recommending a change to a sealed type.

The starter circuit on these cars is very simple.

Ignition switch --> ignition relay --> linear gear position switch --> starter relay --> starter.

As you have replaced the linear switch and you believe the ignition switch is good, the problem could only be the ignition relay or a wiring connection in the circuit which will be easy to test with an ohm meter.

If this is the case, I apologize, I was thrown by the MY and VIN number. Perhaps they used the older system for Australia or for the 3.2L? But didn't bother to document it!!

Cheers,

Allan

 

Hi Allan

My daughter lived in Perth for a few years but now lives permanently in Houston and loves it! My grand daughters are dual US - Australian citizens, having been born in Houston. I am due to visit my daughter and her family within months but not looking forward to the 16 hour flight to Dallas. We're planning sailing through the Florida Keys and onto the Bahamas.

Even Bill Gates could not afford to live in Perth these days. Perth is a mining town with some of Australia's most expensive real estate. Three bed room house rents are around $1,000 per week in some areas.

The date of manufacture of my car is 17 February 1993, which to me is a '93 model, but in the US I think you would call that a '94 model?

What a nightmare the XJ40 electrical system is, after the simplicity of the E Type wiring system. Even the XJ40 tail lights have an ECU!!!

I have a number of XJ40 wiring diagrams, all different. It is the yellow starter solenoid I need to check next but the glove box etc needs to come out first to gain access.

What part does the box in the rear left hand wheel well play in the starting system? Could that still be the problem?

Thanks

Bob

 

Bob,

If you only have one box back there, I reckon it's the ABS ECU. On the wiring diagram I looked at for the 88-92 models, there was no mention of any security system inhibit to the starter. Perhaps the only option for those models was an aftermarket alarm?

I agree by the manufacturing date and the VIN it would be classified as a MY93 which is part of the confusion!! Good old jag

Cheers,

Allan

 

Hi Allan

The box in the left rear wheel well is an anti skid controller or the ABS ECU.

Still no wiser as to the problem.... Back to following circuits.

Bob

 

Yep that's what I thought. In some ways though that is good. I'm pretty sure that your car did not have a factory alarm installed. Did you check the yellow relay?

Hang in there, I'm sure you are getting warmer

Cheers,

Allan

 

Bob,

You might find this useful. These are the starter wiring circuits for the 88-92 cars and the 93-94. It sounds like you have the former in your car even though it is a 93.



Hope this helps.

Cheers,

Allan

 

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