www.jec.org.uk

I apologise in advance for a long post, I'm having some strangeness happen with what I think is the security module.

Drove to work all ok on Wednesday, parked up, and locked with the fob. Five hours later went to pop out on my lunch break and the key fob didn't work. I thought it might be the buttons getting lazy, so used the key, the central locking fired and opened all the doors, rushed to put the key in the ignition and realised that no chimes to warn me I have 7 seconds to comply. Dashboard comes on, and no warnings, but she refuses to turn over.

A couple of things I had noticed Tuesday night though, doors seem to operate the central locking randomly while driving, and the tick tock sound when the indicators work goes at double time which I thought meant one of the bulbs has gone, but all are ok when checking. Driving in to work Wednesday morning and all back to normal haven't had any of those problems since.

I called my breakdown service out as I thought it was the battery and no-one at work had jump leads. The breakdown guy had a look and he tested the battery and said it was ok but just needed a charge. So he connected his booster, but it still wouldn't start. We then realised the immobiliser wasn't deactivating. He said then an ECU reset should sort that, which got the car started, but fob still isn't working.

There was a bit of water in the spare wheel well so I've dried out the interior of the boot (trunk), checked the slcm for shorts etc and it's all ok no burnt out bits. I had to lock it Thursday night with the key as the fob wasn't working and assumed I had to reprogram as had disconnected the module. Thought to myself, I'll do that in the morning. Well yesterday morning without me having to do anything the fob worked! Drove to work and parked up. Fob not working. Locked car up and left it until my lunch break. Went out, fob working again. Drove it to local Tesco, turned car off, fob not working again, went back to the car fob still not working. Got back to work, locked the car with the fob! Came out after work fob not working. Unlocked it with the key, engine wouldn't start, immobiliser still active, opened the boot with the key as the growler button didn't work (although this morning it was working), to disconnect battery and reset ECU and the alarm went off. I put key in ignition to turn off alarm and the car started!

This morning, had to unlock with the key, got the chimes to get the key in the ignition and she started all ok, drove to work, went to open the boot with the button on the dash, which is working, and the display is showing Valet Mode and I get the chime. Had to unlock it with the key (no alarm this time).

It's driving me absolutely batty! Does anyone think it would be worth looking at replacing the SLCM? Or could suggest what else I should check?

I get some of what you describe on my X350...usually in the winter if the battery is low or has failed a battery drop test.

My suggestion would be to get the battery load tested at a garage. If it is marginal or poor, then I would immediately get a new premium grade battery such as a Bosch Silver or Varta Blue. Forget budget batteries. They are not good enough for these electronically dependent cars.

Try that to begin with. A good battery can cure many ills.

Mike

Could also be the contacts in the key fob that need cleaning. That can cause random problems. I’m sure Mike K can explain how to go about it.

Regards.
Ian.

There are a couple of good vids on Youtube about Jaguar key fob overhaul.

Essentially you pull the fob apart, get rid of the dusty muck, unscrew the PC board, replace the battery and clean up the contacts with a soft pencil rubber.

Mike

Thanks for the replies, much appreciated.
I've had the battery load tested and it came up ok. But he did say it could do with a charge overnight, which I'll do later. I cleaned up both the fobs I was given when I bought the car, as they weren't working, but that turned out to be dead batteries and I had to reprogram both fobs.

It's strange as it seems very intermittent, but I have read elsewhere that a good fully charged battery does cure many faults. I've had a Trac Unavail message pop up when I start the car since I've had it which again points to the battery.

I'll post tomorrow after a good charge and let you know if that has helped things.

My old V8 S-type would throw an ABS/DSC message occasionally in cold weather after the first morning cold start. This meant that the onboard diagnostic program had failed to complete successfully. Restarting the car having had the alternator just give the battery plates an initial small surface charge, was usually enough to help the issue. Restarting, the DSC message would not reoccur. In my experience, a new battery and stable voltage platform would usually cure those messy issues.

As said, a premium grade battery in first class condition is essential to cure Jaguar gremlins. Economy batteries are really not good enough and need to be avoided like the plague. They are often good enough in the summer, but come the winter can fail miserably at the task of running an electronically driven and very sensitive car.

Batteries showing less than 12.4v are to be regarded as half discharged. 12.8v is fully charged. Much below 12.4v is marginal performance wise and anything below 12.0v means electronic switch gates fail to "open" and the car will probably refuse to start. I know if my former S-type and indeed my current 350R are used for short winter journeys with heated screens, seats and dipped headlights all switched on, I could and can often start to get gremlins. A half hour run with those services switched off usually sorts matters out. I also know on the 350R if on cold start that if the glove compartment drops open together with the fuel filler cap and the console light stays on, then my battery condition is one of low terminal voltage and I need to do something about getting a good recharge going. Winter conditions exacerbate the issues.

A new battery is sheer joy. Everything works better and system failures and gremlins often disappear. If your battery does not respond to holding a good level of charge, then biting the bullet and replacing is probably the best way to progress.

Mike

Hi all,
Just an update to this, I charged the battery over the weekend, let it sit out of the car, off the charger to see if it held a charge. which it did, settling in at 13.4v. I put it back in after taking the security module out, giving all the contacts a good clean and checking for moisture in the unit itself. There looked to be a bit of corrosion in there which I cleaned off. Put it all back together and connected the battery.

So far so good. Fob still doesn't work, but I can lock and unlock with the key, and the immobiliser disarms when the key is in the ignition.

I tried to reprogram the fob, which I couldn't even get it into the programming mode before, but it isn't seeing the fob as when I press the buttons the light on the J gate doesn't flash. I know the fobs work as I had programmed them both and they worked up until the water in the boot incident.

I think it might be worth throwing £35 at a new security module.