I have a 93 xj6. Could a brake sensor cause my car to go into limp mode? ????

 

tater:

...If it were me, I would already be suspecting the Throttle Position Sensor. They get dirty and they get old, and one that's gone flaky has anecdotally been the source of many a limp mode frustration. But... you can't just start messing about with it because its position on the throttle body must be precisely calibrated. While I have never attempted it myself, I have heard others talk about the trickiness and dexterity it takes to clean or replace while the TB is still attached to the engine. Perhaps somebody else can give pointers.

Meanwhile, there is a great step-by-step write up in the Jag-Lovers XJ40 E-book, which can be found there or in our XJ40 How To Links. Here's a short cut:

Jag-lovers' Ebooks

Also, I have discovered from personal experience that the cube relays can 'go' bad - i.e. it doesn't have to be good or bad, but may be in the process of going bad and thus working well intermittently. So, if you go, for example, to replace the transmission relay as part of your process of elimination, I would replace it with a new relay or at least one that is swapped out from some other non essential system that you know is working. That way you eliminate the relay as the possible culprit.

There's no easy answer to this, sorry. But it can be resolved. Perhaps others will chime in.

Scott

 

Thanks Scott. I am having a really hard time finding this problem. I have replaced all of my relays, my tbs is working I think?? I have had the car running, unhucked the harness to see if the car would die out. It about did then I rehucked it. I have changed the transmission fluids twice. I was wondering if the brake sensors where tied into the transmission warning light an limp mode?? This problem all started when my brake started going bad. One night I had to lock it up to avoid hitting a deer an the light has been on since? ?? I have had my brakes changed, the wire on the brake pad was to short so it is not hucked up? ??

 

I cannot imagine how a brake sensor would have anything to do with the transmission light or limp mode. The brake light, however, might have something to do with the sensor not being hooked up.

What harness, exactly, did you unhook and re-hook up? I'm not following you on that one and it could be important.

Seriously, if it were me (in fact, it has been me in the past!), I would systematically walk myself through the diagnostic steps outlined in the XJ40 E-book rather than taking stabs in the dark. I also don't think you can say the TPS is 'good' unless it is proved good through a serious of tests (outlined in the E-book). A visual inspection won't tell you that. They so frequently get clogged up with grease and gunk from years of sitting underneath a throttle body. Again, if it were me, I might be considering replacing it with a new unit (not cheap, as I recall, though - well over $100) - provided you have the tools to recalibrate the new TPS - and give the throttle body a good cleaning while I was at it.

And all of that is to say, it only 'might' be the TPS... Alas.

Scott

 

I read somewhere (I'll try and find it in a bit) that when the trans light comes on and car goes to limp mode that it isn't always because it detects a problem with the transmission. It is more often the case a problem elsewhere which is usually why the CEL appears, too. Best thing is to check the DTCs. It goes into limp mode to protect from further damage (again, not always further damage to transmission)

 

Thanks Scott. Going threw the transmission check list. It wouldn't surprise me if it was the tbs. Wish me luck.

 

Maybe this can help guide you. There are 7 issues that will trigger a CE/Limp Mode

 

Thanks

 

Would the idle speed control has anything to do with my transmission light coming on? ???

 

I had the same problem with my 1990 Sovereign. I went through the checklist and had my mechanic do what I could not. It turned out that water had somehow leaked into the transmission module and caused the electronics to act up quite a bit. I'm not sure if it is a leaky windshield or if its coming through the air intake for the HVAC system. However, once we swapped the module from my parts car, the car is now shifting fine.