I have searched for a comprohensive list of possible faults that would trigger the famous Failsafe Mode dash warning to be displayed.

This list is only for those failure modes that DO NOT throw an OBD II code.

Is there such a list? I would love to see that sucker.

If not, here is my entry....

1. Radiator fans do not turn on - fuse blown
2.

 

I found this in the TSB. It shows for MY 98 so I don't know if it will apply to your model. Also start at the battery and grounds for electricial issues.

 

Thanks BobRoy. But what I am trying to document is not a faulty light that comes on, but the legitimate reasons the vehicle may go into Failsafe mode but not throw an OBD code to tell you why. The computers monitors real faults (like my blown fan fuse) but does not tell you why. If we at least had the universe from which these codes issue, at least it would limit what should be troubleshooted.

 

There may not be such a list and if there was it might be huge. Any time it gets a few contradictory/wacky sensor values it may be unable to decide which is OK and which faulty and thus unable to flag codes and also unable to run closed loop properly. Also, many codes (by law) need to occur under similar conditions on 2 trips and if that doesn't happen it can be unhappy but unable to flag anything. (Sometimes you get pending codes but lots of people/scanners don't check.) On top of that if the OBD monitors are cleared (e.g. code clear by owner) but there's something a bit odd then it may be unable to set the monitor(s). As they often need to be set before codes can flag you get catch-22.

It helps if you have a mental model of the way closed loop works, the details of OBD etc. And if you get a limp mode / restricted performance / etc type thing without any actual or pending codes but with all monitors set to go through at least all the easy tests (like sanity checks for sensors).

 

That mental model is what I hope to build, and your response helps in that effort. I agree the software is a bit dodgy in how it deals with all the sensor data it receives, and I assume more modern Jags do NOT have this issue, or at least not as severely.

Given that, I would still like to know what conditions initiate the failsafe mode to complete the model so I can either ignore it (saw a post froM an XKR owner saying he had the warning for 133k miles!) Or at least have a clue of where to look.

It may be hopeless, bUT that is my hope. Thanks for the feedback.

 

I think it might be a good thread/sticky to document the found causes.

 

At heart pretty much every modern (petrol) car is along the lines of OnBoardDiagnostics.com - Engine Basics

Some jag info as to what it does when OK, you'd have to figure all the (many) possible failure modes http://www.thejagwrangler.com/upload...management.pdf

The workshop manual has a lot of info but again you'd have to figure failure modes. It'll be many...

I suspect only a few ever happen in practice and realistically it would be great if owners could report which ones they are but I think so few get reported (and not always with the fix) that this is a tough issue for the quite few times it occurs. (In contrast, car not starting is fairly common and there are both flowcharts and posts about that.)