95 XJ12 no crank, no interior lights, no trunk lights
 

1995 xj12, this car has been in the shop for far too long now and the problem has not been resolved. condition is a intermittent no crank when this condition is happening their are no interior lights tied to the BPU, no WCA lights, no audio chime from the speaker to indicate keys/door as well as the trunk lights are out, their is no indicators or hazards either. the vehicle is my bosses wife's car, when they first worked on it they replaced the ECM, BPU, security module and then other components that were not related. i have replaced the BPU as well putting it on its 3rd module now. the gear selector will not come out of park when this condition is present but the P will be illuminated red still. any ideas or info is appreciated.

G'day Jake,

There is an IGN relay in each heelboard fuse box at the base of the rear seats. If one or both of these relays sticks or fails the car will appear to be dead or half dead electrically.

Remove the heelboard covers and check these relays, they should click when the IGN is turned on.

If those relays are good the next place to check is under the bonnet/hood. There is a fusebox about halfway along each fender with a relay in each.

As you sit in the car the RHS fusebox has an IGN relay which should click when the IGN is turned on, if it doesn't then swap it with the relay in the other fusebox and try again.

The problem with these various relays is that the contacts corrode due to arcing and won't connect cleanly. You can take the cover off these relays and clean the contacts with emery paper of just replace the defective ones.

Cheers,
Jeff.

Ah yes I did not think about those relays, the shop is closed for the day so I'll be back at it tomorrow. One thing I did notice when diaging was the check engine signal to the bpu will get pulled down to ground when the condition is present. I know this will not allow the vehicle to crank as the bpu must have a check engine signal. I will check those relays tomorrow morning. It doesn' help that I haven' been able to recreate the condition at all today.

Watto700 ,

You forgot to mention what you found in yours as the battery bus fuses and terminal hardware on the fuse box bellow the B+ battery terminal post and the other one under the rear seat as you remove the seat pan .

Someone found one of the 3 B+ power terminal post on the rear engine compartment upper wall location loose and you can use 3 nuts on the post , the outer 2 tightened to each other so you have something to hold the post from spinning so you can tighten the 3rd nut that clamps the terminal together without going under the dash to suck it all together .

The relays Watto700 refers to is what I call the 5 king relays ( with the exception of the LH engine fuse box which is only used for the horn , swap candidate ) and are closed by a ground provide by the ignition switch though pin 5 to car ground . My pin 5 was corroded .

The easiest way to check these king relays and the ignition switch is to have the key in the on position and walk around and remove a king relay one at a time and reinstalling the same one in hand and you should feel it click . Then move to the next relay and do the same . The LH engine fuse box relay is the horn so it wan't respond . If the relay clicks it verifies than it's getting the correct commanded ground through the ignition switch and on through the pin 5 to the car frame . This does not verify that the relay is any good as the power contacts inside can be bad so have the LH fuse box relay in your hand , swap it and try starting . The most important king relay is the one in the RH engine fuse box .

If you find the relays don't get the commanded ground by clicking you can move on to the ignition switch and pull the connector and as you rotate the key you should get continuity from pin 1,2,3 to pin 5 . Pin 1 to 5 is a spring return contact so the meter reading will waver as it comes off its contact . More then one of these 1,2,3 pins will have continuity at the same time so it gets squirrely trying to figure out but you just rotate the key through and each 1,2,3 contact will close . You can spray some lube inside the key barrel if you don't get your 1,2,3 to 5 as the tumbler can bind and stick on the 4 to 5 key in / key out contact for the car shutdown / go to sleep sequence .

This covers only the power bus side of the mater



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Right you are Lady P,

The problem I had with the battery cable connections only became apparent recently after I replaced an ageing alternator, I had the 'no crank' problem with my car over ten years ago but your post above is the first time a connection between the two conditions has been made. The voltage loss along the battery cable probably accounted for the starter motor not engaging even though the battery was good and the relays were all good. Live and learn.

Cheers,
Jeff.

So I figured it out, it turns out the check engine signal voltage from the dash cluster to the BPU and ECM has failed at somewhere, I'm thinking driver or their awesome old TI processor. Another question now, does this vehicle require reprogramming when replacing the dash cluster?

Did you check the fuse for the instrument cluster in the LH heelboard fuse box # X . And # 5 / 10 amp trunk . Mine was blown before .

I have found the issue, one of the drivers I believe or the ti processor of the printed circuit board of the IP Cluster has an intermittent fault which results in the check engine signal voltage being sent to the BPU and ECM to be pulled down to around 1.2 volts. Their should be ground when active and b+ when inactive. The BPU controls cranking but will not allow cranking if it doesn' get the check engine light signal from the IP cluster. When cranking is to begin it will shut down all interior lights and so fourth as to provide as much current to the starter. It is essntially stuck In a state of thinking it' cranking but the bpu will not provide a ground for the starter relay until it sees the check engine signal. Thankfully it is been diagnosed so now I can put this out if the shop and move onto something else till my boss provides the new circuit board or a remanufactured cluster, or he has this one repaired.

Really useful diagrams, thanks for these!!

Whats an IP Cluster? i have the same problem now. i dont know how to solve it. if you please can explain more on the steps. thank you

Instrument panel cluster

With the key in the on position before the start position walk around the car and remove the king relays one at a time and reinstall in the sockets and you should feel them click verifying they are getting the correct command to close providing power to the sections of the car

These king relays are the ones in the corner of the 5 fuse boxes . The exception is the one for the left engine fuse box which only controls the horn so is a swapping option

If you look at the many fuses in each fuse boxes about half of them are hot at all times from the battery cables and the other half must have the king relay's close . The left engine fuse box is an exception

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Thank you Parker 2 for the quick response.
I already have done that. i even tested every relay of them and some other relays like the starter one. also, checked the fuses. they all are fine. and battery is only 6 months old and recharged it.

I have a 1996 Daimler Double Six. it is considered to meet the standards of ROW. LWB and LHD
it doesnt have any oxygen sensors. it doesnt have a secondary air pump.

the car has been worked under many mechanics before. i discovered later that the security module and incline module are not there. yet, the car was running. they installed a universal door lock remote to the car connecting some wires to the LH rear Heelboard.

one of the fuel pump wasnt working. so i changed both of them. it worked all right until i found some radiator leaking from one of the top hoses connected to the resevoir. i changed it but found the water to fill the crank position sensor`s connector. i am thinking it caused a short there. i cleaned it. but still .. the car wouldnt crank. no headlights, no interior lights. i am sure there is something went wrong.

as this car was a project for me after what it has been through, i renewed most of the components.

the Starter, fuel pumps, fuel filter, air filter, spark plugs, spark plugs wire, and all radiator hoses are new. fuel tank, fuel lines, throttle, radiator, and fuel injectors are cleaned.

now, i ordered new crank sensor and a cam sensor. waiting for the them to be delivered. until then, i really dont know what would be the problem.
i tried to pull out some codes. they keep changing since it was running. but most of the time i get the codes for the MAPS sensors circuits being high and low voltage.

G'day Abdullah,

Another place to look at is the security of all the connections in the lead from the battery to the starter.

I had a similar problem to you and the battery lead having loose connections was the problem.

Starting at the battery check the battery post and then open up the fusebox there and ensure everything in it is clean and tight.
The next connection is under the rear passenger seat on the RHS, there is another fusebox with two heavy duty fuses there, they need to be clean and tight.
Now in the RHS front footwell close to the transmission tunnel is a connector which passes through the firewall, it also needs to be clean and tight.
The connector on the starter itself should also be clean and tight as should the connector on the alternator.

My no crank problem and was cured after I checked the battery lead security as was poor charging of the battery, I was losing nearly three volts between the alternator and the battery.

Cheers and good luck,
Jeff.


P.S. I have just read through this whole thread again and it appears that I have already given this advice previously. Ooops, too many birthdays behind me.

Most of us with these V12s have had too many birthdays to remember everything.

Another thought, if when you test a relay and it clicks, indicating that it has closed the contacts, that doesn't mean that current will flow. If the relay has dirty or corroded contacts then good contact cannot be made and no current will flow.

In the LHS undebonnet fusebox the relay there is for the horn, you can insert any relay you want to test in that socket and try and sound the horn, if it sounds strongly then that relay is good.

I've managed to resurrect dead relays by taking the cover off and using fine emery paper to clean the contacts

Cheers,
Jeff