Should it always throw a code when it drops into failsafe engine mode?

The light and message came on on the way to work today. No symptoms that I can see. When I got in I put my code reader on it (before turning the engine off): the reader is denying any stored or pending codes. Turning the engine off and back on cleared the failsafe mode.

I'm now left with the question of whether it's the car imagining things, Jag being unhelpful, or my cheap and cheerful code reader not reading what the car's telling it. None of which is a particularly attractive option....

 

My code reader (OBDCOM) would not read a code for failsafe mode either. Each time i restarted the car the failsafe mode was gone and would return while driving. No change to engine performance but the cruise control would become disabled. My problem turned out to be the brake switch ( thank you Forum members for the info) and I was able to fix it just by spraying some WD-40 into the switch at the plunger. No failsafe mode since then

 

The problem is that your OBD reader only reads 'P' codes (powertrain) and other things can set codes you can't see. Some (like ABS and airbags) will trigger warnings but others won't.
Check your battery is good - that can cause odd behaviour - and let us know what happens.
If you haven't already download JTIS https://www.jaguarforums.com/forum/x...archive-65998/
for a goldmine of info.

 

Rocklandjag has your probable answer, but I'll add that the fault code usually set by a brake switch is P1571. That is a corporate code, meaning it's not an SAE mandated standard code. Lots of generic scantools can't read that fault. And I think, thus your situation.

Good luck!

 

It did it to me twice more today, and this time I was paying attention. Both times the light came on as I touched the brakes. So it sounds like the switch is the cause. I've given it a good dose of CRC and we'll see what happens.

Thanks guys, this forum's great.

 

If contact cleaner doesn't fix it there's a sticky on changing the switch which is a pig of a job
https://www.jaguarforums.com/forum/x...ics-faq-37758/
with a follow up
https://www.jaguarforums.com/forum/x...allenge-83605/
Someone fixed their switch by bending one of the microswitch levers so both switches operated synchronously but I can't find the post.