I recently purchased a 03 str thats stuck in limp mode with all the faults i.e engine system fault,park brake,dsc not available. It had a new throttle body installed and no change and also changed the connector to the tps sensor.What i found is there is no power at the f18 throttle fuse when key is on. I repaired The connector to the throttle motor which was broken and zip tied. Is it possible that the driver in the ecm for the throttle motor may have been damaged?
I have checked the wiring integrity to and from the ecm and there is not breaks or shorts. Also checked the wiring from the relay to the fuse and its good.
Is there any other checks that i may be missing to narrow it down?

 

Do you have any fault codes? However many may help.
When the throttle body was changed, was the tps also changed or did you use the original one. The reason I ask is I read here about it may need to be re-coded or something of that nature.
Have a look at post number 6 here:
https://www.jaguarforums.com/forum/x...-react-188109/

 

The fault(s) described would normally cause codes - really not got any? Not even pending ones?

BTW that thread is about a very different jag. Ours will not show 0% (by way of example).

So far sounds like someone throwing parts at it rather than diagnosing. Gets painful and costly very fast.

You've checked the workshop manual about the various issues? It gives lots of info and tests.

 

It has p0121 code.

 

Wiring diagrams here:

http://www.jagrepair.com/images/Elec...al%20Guide.pdf

Scroll to section 3.5 for details about fuse F18. I wouldn't worry about the output to the throttle motor until you figure why the ECM is not receiving the correct 12VDC input via that fuse. My mindreading skills aren't what they used to be, but I think you may be following the current flow in the wrong direction.

Look at relay R4 (Throttle Motor Relay). It controls that required 12VDC input. Battery power (via fuse F9 in the front power distribution box) should always be present at contact 3. When the relay is energized, contacts 3 and 5 are connected, and 12VDC is fed to the ECM.

To energize R4, 12VDC must be available at contact 1. This comes via the same fuse F9 feeding contact 3, but it also passes in series through relay R5 when it is energized with the ignition switch in the run position. Contact 2 is the control for the relay, a ground supplied by the ECM.

Testing the inputs to the relay is easy:

1) Start with the ignition off.

2) Remove relay R4 in the front power distribution box.

3) Check for 12VDC at contact 3.

4) Turn on ignition without starting the engine.

5) Check for 12VDC at contact 1.


Testing the outputs is a bit trickier, as you'd have to trick the ECM to supply a ground. Let's skip that for now.

If the relay's two power inputs are good, let's swap relays with a known-good one and see if that fixes the problem. Relay R18, for the windshield washers, should be the same type of relay. Test your windshield washers to make sure that relay is good. If so, swap that relay to position R4 and let us know what happens.

 

Ah, here you go:

http://www.jagrepair.com/images/Auto..._OBD_II_R2.pdf


Scroll to page 17. With that fault latched, the ECM will not send the ground signal to energize relay R4. The lack of power at fuse F18 may therefore be a normal response to a fault condition. I'd still check for power to the relay as described in my previous post, and swap the relay for giggles, too.

After that, here are your possible causes, from the far right column in that chart:

TP Sensor to ECM wiring: open circuit, high resistance

TP Sensor to ECM sensing circuits (TP1 or TP2): short circuit to B+ voltage

TP Sensor failure

 

+1 on this question. For code P0121, a bad TPS is the most likely culprit if the wiring is okay. This doesn't mean rush out and buy a new sensor, but it should direct the next troubleshooting steps.

 

I checked the voltage on the relay r4 I've got both key off pin 3 and key on pin 1 voltage. I've tried a few know good relays and no change.

 

Okay, making some progress. Unless you've got a bad socket for that relay (not very likely), it sounds like the ECM is deliberately not energizing that relay due to the TPS sensor fault. Please see post #6. No voltage at that fuse may not be an actual fault itself, but a normal ECM response to a different problem in the TPS circuit.

We're going to need a little help from you. Long-distance diagnosis is tricky at best. So for the third time (hint, hint) did you change the TPS or is it the original one swapped over to the new throttle body?

 

I'm not sure about the tps sensor. I got the car from someone who got it from someone with the issue of stuck in limp mode and the add said a new throttle body was installed. It does look new but Who knows. I did order a new tps just waiting for it. I've checked the wiring per the jtis and the only thing that doesn't jive is the resistance values between pins 2 and 4 and 3 and 4 on the tps sensor itself , according to the jtis the values should be the Same mine are not.

 

Sounds like you are hot on the trail. One caveat, but I can't access JTIS to be sure. I could have sworn the two circuits inside the TPS operated opposite from each other, and then the two values were added to make sure the signal was valid.

For example, circuit A would read 0 units with the throttle closed, and 100 open. Meanwhile, circuit B would read just the opposite, with 100 closed, and 0 when open. At any throttle position, the sum of the two values would always be 100. If not, at least one of the circuits had a problem and the ECM would respond by going into a protective mode. Hopefully somebody more in the know can chime in. Maybe I'm thinking of the gas pedal, so please don't read too much into this until you get confirmation.

 

I will know more when the new tps shows up. If that doesn't work then I need to figure where to go after that. I have another 03 star that I may be able to swap throttle body and see what I get.

 

If your other str is the same, do the readings on that tps first and see what you get in comparison to the other one.
Same for the other things KR98664 has suggested.
If it's possible to do it that is.

 

Ok I replaced the tps sensor and still have the faults. Now I can see the tps signal % on live data but throttle only lets it go up to 2000 rpm.

 

That could be where the safe zone is, not allowing you to rev the engine high until it is actually moving.
It might be 3000rpm though now I'm thinking about it.
Mercs do the same. Without the wheels turning you can't rev the engine any higher than 3000rpm.

 

I'm assuming (Danger! Danger!) previously you couldn't? If so, that's more progress.

Are you still getting the P0121 fault?

I wonder if the rev limit is a leftover thing from the bad sensor putting the engine into restricted mode. Have you disconnected the battery yet? If not, the poor ECM may be thoroughly confused, only seeing a change in the TPS sensor, but totally unaware it is now (hopefully) correct.

This calibration procedure may be required now, whether you've disconnected the battery or not:


https://www.jaguarforums.com/forum/s...ection-176446/

 

So im still getting the p0121 code. ive checked all the wiring again per the jtis and everything checks out. Ive disconnected the battery and tried the calibration.
I am going to leave the battery disconnected overnight and see what happens. one other thing i had tps signal once i put the sensor on but now i lost it. it stays on 2.7% even though the throttle will go slowly up to 2000 rpm as i press it but no matter how far its pushed it goes no higher than 2000 rpm. i figure its because the limp mode.

 

TPS is created by the PCM from TP1 & TP2, which for safety (redundancy) report different values.

I would not want to mess with either TP1 or TP2 as codes are likely.

(The APP is done in a like manner.)

 

Well, sorry this isn't clearing up as quickly as one might hope. Don't give up, though, as you have been making progress.

It's odd you had a good TPS signal and now it is stuck. Was it showing the same 2.7% with the previous sensor?

It's rare, but new parts can be bad from stock, leading to a troubleshooting nightmare. That's why I'm curious if the new sensor is showing the same value as the old one. If it changed, even if still bad, that would point to the new sensor being bad. (Remember, it's probably been sitting on a shelf for years, so it may have corrosion inside.) If the value didn't change compared to the old one, then the fault likely lies elsewhere.

You mentioned having another STR. If it runs well, you can use that as an Alabama blueprint, to take a reading of what a good sensor should indicate. For the moment, I'd hesitate to swap any parts over from the good car, on the slim chance an electrical fault is burning them up. But you can easily compare sensor readings.

I'd also suggest disconnecting the TPS and watching the resistance values as you manually cycle it. Normally I prefer a digital meter, but this is a perfect application for an older analog (needle movement) meter. You can easily watch for erratic behavior as the needle moves.

Can you get some electronic cleaner spray inside the sensor? Take resistance readings before and after, and see if anything changes.

How about the connector for the TPS? Maybe it's not making good contact? How about leaving it connected and taking some readings from the ECM connector? Then the meter would see exactly what the ECM is seeing.

Last thought was the battery. In your first post, you mentioned getting all the other messages one typically sees with a marginal battery. The post-facelift cars seem to be especially susceptible to this. Perhaps the ECM won't properly reset after a fault if the battery is not up to snuff. I'm not saying to shotgun a new battery, but if your other STR runs well, then you've got a known-good battery you can swap for troubleshooting. Could be you're dealing with two faults. You've fixed one (the TPS sensor) but the second fault (battery) is still active.

Other than that, I'm about out of ideas. I've got no special experience with his particular drive-by-wire system. I'm only offering some general electrical troubleshooting suggestions that could apply to nearly any system. Anybody else got any thoughts?

 

Almost forgot:

Are you ever seeing power to that fuse? If not at the moment, check it again if you ever get a valid TPS sensor again, even if the engine still won't run correctly. My hunch is the ECM inhibits that relay if it sees a critical fault, such as the lack of a valid TPS signal.