Intermittent Gearbox Fault

[ianfullick434]

Went back to the garage yesterday and they confirmed it was code P1260 Security Input that was found, and the relay which was replaced with a new black Jaguar item as shown in this picture.

[Astromorg]

That explains pretty much everything I think! That relay is one of the 'Big Beasts' of all the relays. Each fuse box has one and they supply the Ignition Switched Power to all the systems and other relays that are powered from that box. For the one in question, the Engine Compartment Fuse Panel, the supplied systems include the Transmission Module (Hence the original MIL?) and the Starter Relay and Fuel Injector Relay (No Start!).

The P1260 would have been caused by this - Loss of ignition switched power supply to the ECM PIN EM82-09 for greater than 16 milliseconds, which was part of Andy's earlier list of the possible causes.

If the relay had failed completely, it would probably have been easier to identify, but an intermittent fault can be as elusive to find as this one was. Definitely one to put down to experience and try and recall in any similar scenario.

Well done the garage that sorted it.

[ianfullick434]

After months of trouble free motoring the old problem came back yesterday. The car would not start after a short stop, the usual read outs were gearbox fault, traction control failure then engine failsafe mode. I removed the 'new' relay which was quite hot, replaced it and after about 15minutes the car restarted. Does anyone have any idea why the relay would get so hot?

[andypryce]

What an absolute pain. I guess relays could get quite warm simply due to the current flow, but am no expert on this.

[JimMann]

Hi Ian, earlier in the process I asked about the condition of your battery but I don't see a post updating on that potential issue cause. I cannot stress enough the number of 'faults' that are caused due to a battery that is past its prime - which is typically over 5 years old.

The list of fault messages you have is VERY typical of those reported by a poor condition battery, all cured by a new battery.

Jim

[ianfullick434]

Thanks for the reminder Jim but I did have the battery tested and it was at 75% and considered by the 'expert' to be in satisfactory condition.

[JimMann]

Hi Ian, that's good from the expert, but typically a battery is dead on its feet at under 70%, so yours will be very close to giving up the ghost.

Of course the car will still start and run, but the variety of fault messages that can be thrown up as the voltage drops away will surprise you. Have a look around the Forum, not just the Modern XK and you will find lots of 'Changed the battery as advised and hey presto, all the faults have gone!'

Jim

[ianfullick434]

Just to catch up, the car again refused to start after a short journey but I had purchased several replacement relays, I therefore replaced the black relay immediately with a replacement and the car started. Does this rule out a duff battery? Does anyone have any other thoughts on why the relay would get hot and then fail but once the relay cooled it worked again.

[andypryce]

Could it be a loose connection to the relay, ie underneath the fuse box? This might explain it getting hot?

[ianfullick434]

Thanks for that Andy I will have a close look.

[Astromorg]

Ian, looking at the circuits involving this relay, there's nothing out there fed by it that should cause a particularly high current to heat the relay because each circuit has an appropriate fuse that would blow before the relay was overloaded. Similarly there's nothing in the relay coil circuit that could obviously create an excessive current. I think that does, as Andy suggests, perhaps indicate a corroded or loose relay pin connection that heats up and therefore increases the resistance to the point when insufficient current can flow. The fact that the relay overheats also shows the heat source is close to it - ie one or more relay pins?

Another point to consider is the quality of the relay(s) - cheaper versions can some times use thinner material for the pins resulting in a looser fit. Have you tried using one of the other original brown ones to see if it's a better fit/performer? The one in the adjacent position is the horn relay that probably hasn't been over used!