Every now and again, out of nowhere, sometimes while sitting at a traffic light, sometimes while cruising along, all of a sudden I'll get the FAIL SAFE warning and reduced performance.

I pull over, shut down, restart and it goes away. Minor inconvenience but I'd like to figure out why it happens at all.

Any ideas or suggestions?

 

Hi
What is the exact wording of the warning alert? Was it Restrictive Performance? Does it go into limp mode (poor acceleration)?
Please provide more information.
Jim Lombardi

 

Yes - fail safe - restricted performance/limp mode. But when I shut down and restart all is fine again.

Can't tell you exact wording because it hasn't happened in a week or so.

 

Steve,
Hard to say what you have going on and I have no idea the year and model of your car, please add it to your post. I would also recommend that you take your car to a place (I have no idea what state or country you live in) and get the codes from your OBD II. When you get the codes write them down so that you can tell us what you have. We want to help but to give you advice now without all the information is just a shot in the dark.

 

The first step to a 'decent' diagnosis (no wild *** guess) is to get the codes read, you can either purchase your own scanner, or take it to an auto parts store and ask them to read it for you. Come back here with your lottery numbers for additional advice. g'luck!

 

Sounds like an intermittend knock-sensor failure to me.
(Had the same experience a while back.)
But as Gus stated it right, w/o the codes it all is reading the crystal ball.

David

 

my bad for incomplete info: the car is a 2000 XJ8 - 117K miles

Will have to see if I can get the codes read without spending an arm and a leg. My recollection is in California (where I am) there's some kind of rule that auto parts stores can't read codes or something goofy like that.

Will codes show up when there's no current warning or restricted performance?

 

Autozone, PepBoys, Sears and most local auto repair garages can read the codes.

 

Read the codes, I had the same issue and it was the accelerator position sensor (code P1122) which meant replacing the throttle body.

My advice, buy an ODB-II code reader, bluetooth models are only $30-50 if you have a bluetooth-enabled device (Laptop or Android phone - no iPhone though)

 

If your check engine light has ever come one during one of these events, the codes will be stored and your local large parts store can read them... if the CEL has not come on, you're not going to have codes.

Usually when reduced performance mode comes on, other error messages scroll across the display - gearbox fault, asc fault, trac control error, etc. Have you seen any of these also?

I had the same intermittent problem for several months (especially when wet or moist outside), with no CEL... eventually the period between events decreased to minutes and finally I fineally got a CEL - which allowed me to read the codes and zero in on a mis-reading from the Throttle Positon Sensor - turned out to be moisture in the TPS connector - cleaning the connector pins and lubing the connector's o-ring with dielectric grease to prevent future moisture incursion has cured the problem for over a year now.