There has been a lot of noise lately about electrical issues and the Limp Home mode that these cars will go into. The Limp Mode is actually an enhancement to engine control computers that has gained traction over the past decade or so. I can remember way back when in the 80’s when engine control computers first started to make an appearance. If a sensor shorted or got a reading way out of scale, it would either fry the computer or cause it to shut down. This meant the car would shut off. Dead. Nada. That would be real scary at 70 on the highway as well. The more advanced the systems became the less frequent this issue was, but it still would happen. Recently there have been enough advances in computer technology that what was unthinkable at any cost in the 80’s is relatively cheap today. So, now when a computer detects a critical reading it doesn’t just shut down, it goes into “safe mode” allowing the vehicle to basically run, but in a limited fashion. This is much better than the alternative, a total shutdown.
So why would I post? I don’t have any issues with my car. The owners here who have had problems are having them taken care of. It’s just that there are things that I do as part of taking care of a car that I don’t normally talk about. Why? ‘Cause some people would think that I’m way to **** with too much time on my hands. See, with every computer car I’ve ever had, I “maintain” the harness. This simply amounts to cleaning and protecting the under hood connections a few times a year. What I simply do is pull each visibly exposed connector one at a time. I spray off the contacts with electrical contact cleaner. I then spray the connector with die-electric grease. I also inspect the connector and socket for loose wires or gaps / cracks / pulls where the wire enters the connector or socket body. These I repair with either silicone adhesive or my favorite, liquid electrical tape. I then plug it back in marking the connector with a grease pen so I know I’ve done it. Then I move on to the next one. I have had very, very, very few computer issues with my cars. American or Foreign. The last step will make some cringe. I then spray off the engine with cleaner and hose it off. This washes of the marks on the electrical connectors as well. Maybe it’s dumb luck that I have very few computer issues, maybe it’s this goofy habit of mine. BTW: I started doing this after my 1983 Monte Carlo kept blowing up computers. I have done this twice on my Jag so far. Including taking degreaser and a hose to the engine compartment. I drive about 1400 miles a month in my car. It’s a daily driver like the Honda before it. Another thing I do after washing off the engine is spray it off with the air hose. (If a compressor isn’t handy, I’ve also done it with a shop vac. Put the hose on as a blower and you’ve got it) I haven’t had any codes or anything else pop up.
The only warning issue I’ve ever had with the car is a DSC / ABS fault. That triggered a few days after buying the car. Ends up, I turned too quick in the rain, activated the DSC, witch activated the ABS, witch triggered the fault codes. Ends up, the DSC computer forced the ABS to react, revealing a flaw in the master cylinder. Dealer replaced it. No more errors. Even tested it out real hard in the snow.
So, I was also talking with my service manager. After reading about the various electrical gremlins that people have, I figured I’d ask him how they clean up the engine compartment of a Jag. He chuckled and said, “Umm, with a $2.98 can of Gunk and a hose”. So, let me get my Nomex suit on, just in case there are some flames shot my way. Anyway, hope some of you find my over **** habits helpful. At least, hope it helps some of you get your confidence back in your car.

 

Appreciate your post, but there is no f***ing way that I am letting a hose, a pressure washer, or even a damp rag get anywhere close to the engine bay in our S-Type. I've always degreased and hosed off all of our other vehicles' engines and then blown them dry, but not this one, no way, no how....

When it's time to clean the engine, I'll do it with old towels, a little bit of silicone spray, and a lot of elbow grease. Yes, that sucks, but I'm not taking any chances....

I think you've been lucky. You can clean the electrical connections that you can see and readily reach until the cows come home, but there are many, many more connections that you cannot get to in order to clean....

Hope you continue to avoid the infamous "limp mode" issue. Designed to protect the engine components or not, it can be dangerous as hell if it strikes at an inopportune moment....

 

Yes, but less dangerous than the whole car shutting down completely....
Also, doesn't apply the brakes, just like a stall, yet you still have power steering and brakes... So, I'll take the new way over the old. And YES I have been in a car that died on the highway at 70. I've had a front tire blow out at 80. I'll take the "new" way over the old any day. Any damn car can die at any time... I feel better driving one that will limp before it dies!

 

Where do I stand to avoid the flames?

 

Just put a fireproof suit on!

 

I have no problem WHATSOEVER with limp mode if the vehicle is actually experiencing catastrophic failure. #1 that is VERY rare, and it makes sense for a car to do such given that particular situation. However, i believe you are missing the point...None of us have experienced this kind of failure, it is nothing more than a sensor getting tripped. With all of this advanced technology that you speak of, wouldnt you think they could just get it right and not have the car decide to shut itself down when in all actuality there is not a damn thing wrong other than some sensor, in turn stranding us on the side of a highway (given that you can LIMP your way off of it)?

 

Actually, I don't think I have missed any point. I think you missed my point. In the case of a throttle position sensor, in the "old" days that would cause a vehicle to cut off, or at the least stutter real bad until it stalled, no matter how fast it was going. The other point is water intrusion is mentioned. When that occurs, there is a potential for a short. Shorts have the potential to fry electronics. So, the issue you've had is a serious one. Not as minor as you think. Now, oil temperature sensor tripping and causing a limp mode would give me reason to flip. There are only a few critical sensors, even in very complicated cars like Jags. A couple of those are the MAF and Throttle Position sensors. They control things like ignition timing. Why the car goes into "limp" mode is it is given a few basic instructions, so it will run. But it won't respond to throttle inputs until the error is corrected. Don't get me wrong, I have empathy for those put into difficult situations. I've been there myself. It sucks. My whole point is that the car reacted correctly to what it thought was a critical failure. It is a great bonus that these cars will react to a failure without totally cutting out leaving the driver without power brakes or steering. Again, I've been there. Believe me, I've even double checked the TPS connector, despite my maintenance habbits. There is no sign of water intrusion on mine. The other point is, every other person I've talked to outside of here, including the dealer, has said it is perfectly fine to clean under the hood.

 

I'm maybe lost..... is this the sensor (TPS) that in effect confirms how open the throttle is? The car has a throttle pedal and throttle motor, doesn't it, so they're sort of irrelevant here, right?

It also has a MAF, so has a fair idea of the air coming in. When MAF and TPS disagree, can't it fuel midway or something, then look at the HO2S (oxygen sensors) and see whether it's too lean or too rich (as it would do in normal running), then figure out which of MAF or TPS is faulty? And then trust the other one.

It would have to restrict performance a bit, I'd expect, but not to 10mph or whatever it is.

(Obviously, error code(s) need flagging.)

OK, what am I missing? (Grabs flame-proof garb.)

Or is this the kind of thing a future PCM software revision might do (in theory; if there were more S-Types)?

Would the MAP also tend to confirm which sensor was OK?