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I have a 2000 MY S-Type with 4 litre V8 engine. I was having some occasional battery problems with slow or no cranking - usually resolved by charging the battery. Then I started to get an intermittent no crank. Switch on, dash lights up as normal, turn to crank and nothing - fuel gage drops to zero, most of the dash lights go out. Keep switching on and off and randomly it cranks enthusiastically and fires up and runs no problem. I fitted a new battery as most forum posts here and elsewhere suggest that as a start point. New battery fitted, earth and power connections removed cleaned same time. Still occasionally no crank - if anything, problem was becoming more frequent.
Have had many weird and wonderful suggestions made, mostly very complex ones. However, as a shade tree mechanic I like to think it is the simple stuff that gets you - and that's true maybe 3 out of 4 times. So, battery is good, no codes or alarms, but occasional no crank suggests to me a poor power supply (already covered by new battery and cleaning connections) or a relay or solenoid problem, or a poor wiring connection. So I looked at relays - there are loads of them on the Jaguar, in three separate fuse boxes, but fortunately only two different types are used - the larger yellow cube and the smaller yellow cuboid. Off You tube I found a video which showed which relay is which - this will have been probably 90% correct (sadly the Owner's handbook tells you which fuse is which but stops short on the relays). I found out that in the under-hood engine fuse box (LHS at front as you face the engine on an S-type, not sure on XJ or XK) relay R15 is the starter relay - it is one of the larger yellow cube type. The lid of the fuse box tells you what the relay numbers are. Swapped R15 for a used relay bought off auction site for £5. Problem is now fixed. Worth a try as simple to do and very cheap.
BTW if buying a used relay then worth getting two so you have a ready spare - and v unlikely that you would get two duff second hand relays. I also noted the Jaguar uses the long reach J-type fuses which are not very common, so worth holding 1X 20 Amp 1X 30 Amp and 1 X 40 Amp as spares if you are keeping the car. Also v cheap used.
I originally made this post in the XK forum in response to another member's request for help on a no crank problem - drive trains are mostly the same for the V8s - but thought I'd repost it here for the S-type users. Not entirely clear on the protocol for items that cross the forums in that way.
PS am loving the car: like most of the bigger engined Jaguars, it can waft along like a limo, or lift up its skirts and drive like a hooligan. Am wishing I had the S-Type R now, but then I'd be spending money like a drunken sailor on shore leave!
Swapped R15 for a used relay bought off auction site for £5. Problem is now fixed. Worth a try as simple to do and very cheap.
Very nice write up. Thanks for letting us know.
Several minor points to consider:
Do you still have the old relay? Pop the cover off. If the contact points were arcing, you’ll see burn marks inside the cover. There are other possible failures with a relay, but if that was it, it’s always nice to have confirmation.
Inspect the prongs of the old relay for signs of overheating, typically dark discoloration. This means heat may have affected the female sockets in the fuse panel. In mild cases, it causes a little oxidation. Simply removing and replaciing the relay is often enough to restore a good connection. In severe cases, the temper of the sockets is affected and they no longer grip well. In those rare instances, sometimes you can squeeze the sockets a smidge tighter with fine pliers and restore good continuity.
For troubleshooting, you can swap with a known-good relay from another system. The fog light relay, for example, makes a good donor for any relay of the same size. Can’t remember if it’s the same as the starter relay, though.
The relays are industry standard items. Bring your old relay to any parts store and they can easily match up something for you. Stay away from el cheapo versions, but any name brand should be fine. Jaguar stamps their name and part number on a standard relay with gold-laced ink and then sells it to you in a diamond-encrusted box.
KR Thanks for your response - I especially liked this bit: "Jaguar stamps their name and part number on a standard relay with gold-laced ink and then sells it to you in a diamond-encrusted box." ha ha had me grinning like a Cheshire Cat.
I'll take a look at the old relay - did not realise you can open them up like that.
Norri Thanks also for your response and that electrical link which I know is going to save my skin at some not too distant point (based upon my previous love-hate Jaguar relationships).
I really do love Jaguars (Grace, Space, Pace), but you definitely need a good forum if your going to own one!
Thank you for posting the report of your successful repair. For the benefit of others who may find your thread (or your similar post in the X100 forum), it is important to know that Jaguar uses relays with a resistor (and sometimes also a diode) wired in parallel with the relay coil. This resistor helps to protect the control module switching transistors from the large voltage surge that occurs when the magnetic field in the coil collapses when the relay is de-energized. If a Jaguar owner replaces one of these relays with a new one of the common auto-parts-store type that has no suppression resistor or diode, the transistors in the associated control module can be damaged, requiring a far more extensive repair than a simple relay swap.
Below is the starter relay schematic for your 2000 S-Type from the manual Norri provided the link to, showing the resistor in parallel to the coil (between relay terminals 86 and 85). You can see the actual resistor in the photo kr98664 posted.
09-17-2022 | 05:10 AM
S-Type occasional no crank - now fixed
