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You might want to start with just the physical basics to rule them out first.
The error doesn't seem to be pointing at the throttle pedal assembly nor the throttle position sensor in the throttle body.
Seems to be eluding to those knowing where they are but the throttle motor not moving in response to a change in the pedal input.
So I apologize in advance for the following detailed suggestions........
Undo your six wire throttle body connector (Plug EN10) from the throttle body assembly
Measure the resistance between pins 1 and 2 of the electrical connector on the throttle body (that will measure the continuity of the throttle motor).
You should get a low resistance (a motor like that will probably give you a resistance of 50 ohms or less - even as low as 10 ohms).
If the motor appears good, then you should check the continuity of the wiring of the harness back to the ECM (Engine Control Module). This is where it gets detailed...sorry.
The ECM has one large single 134 pin connector going to it (EN16 - see below).
It is held in place by a single weird Torx type headed screw, so to undo you may need to buy the specific driver as standard Torx doesn't fit. (now you might be able to use a sharp pin to pierce into the red and green wires at the ECM plug so you can create a quick measuring point without having to initially undo the connector).
What you want to measure is the continuity of the red wire then the green wire that go between your throttle body plug EN10 pin 1 (red wire) and pin 2(green wire) to the ECM plug EN16 pin 80 (red wire) and pin 106 (green wire).
Check continuity/resistance of EN10 pin 1 to EN16 pin80 with your meter....you should get a very low reading of under 2 ohms.
Next check continuity of EN10 pin 2 to EN16 pin106 with your meter....you should also get a very low reading of under 2 ohms.
If either is high or open circuit you probably have a broken/damaged wire in the loom.
If both are independently measuring low, then they are probably good.
While the throttle body connector is still disconnected from the throttle body measure between pins 1 and 2 of EN10 throttle loom connector, that should effectively measure very high resistance (open circuit).
If that measures very low, then you either have a short in the wiring loom between red and green wires or a damaged ECM drive circuit.
So, if the ECM plug EN16 is still disconnected from the ECM at the time you measured this, and you still measure a low resistance between pins 1 and 2 of the throttle body loom plug, you have a short in the loom between the red and green wires.
If the motor is not open circuit or shorted, and the wires have no shorts between them and normal continuity from Throttle motor to ECM pins 80 and 106, then it is starting to look like an ECM driving circuit issue (which would be very rare)....hence the pains to rule as much out as possible first.
Let's see what you find initially with these measurements.....we can then see where it leads from there.
Do you get any throttle body movement at all in response to the pedal being pressed?
Or does the throttle butterfly just maintain a fixed idle position?
Do you know if the relay R11 is being successfully switched on?...are you getting 12 volts out of R11 pin 5 appearing on power distribution box plug JB1 pin 39 (green wire/ red stripe)?
If the Relay R11 is not being turned on, then it would appear the ECM is not allowing throttle to be used - as the coil for R11 is switched from the ECM.
Hard to know at this point if the issue is a throttle component issue (TPS or pedal sensor) or a side effect perhaps of a security feature.
If R11 is being activated, then I think we are going to start hunting the pedal voltages to see what is going in and out of the pedal sensor assembly ( two supply feeds, two variable outputs and two negative returns) that all tie back into the ECM.
Let's see what you can confirm regarding R11 activation...then we can go from there.
Between my job and other distractions, I havent messed with car for days. I will tell you what I do know now, and hope to finish the thing Im working on now and get to the Jag later today or tomorrow. When running it responds to just a little throttle up to 2500 rpm. more throttle changes nothing. the blades of the TB are not opening much, if any. the previous tests you gave me were normal, but thats as far as I got before. Thanks again for your help. I will let you know what else I find from above.
Yeah, this time of year can have you pulled in so many different directions!!
OK, whether or not you are getting some movement in response to pedal activation, if you want to check out the pedal and throttle body sensor behaviors then it is worth checking the voltage coming out of the new pedal assembly being sent to the ECM.
The pedal assembly has two variable resistors within it, so there are two independent readings to be looking for.
Pedal sensor 1 output can be measured on the red wire at pin 4 of the pedal plug PA1 or the red wire at pin 102 of the ECM plug EN16.
The voltage range should swing from 0.97v volts with pedal in the rest position and 3.33 volts when the pedal is fully depressed.
Pedal sensor 2 output you can measure on the yellow wire at pin 1 of the pedal plug PA1 or the yellow wire at pin 103 of the ECM plug EN16.
The voltage range should swing from 3.97v volts with pedal in the rest position and 0.84 volts when pedal is fully depressed. (Note: the voltage swing on sensor 2 moves in opposite direction to sensor 1)
If you have the right voltages coming out at the pedal, just confirm you have them getting those values back to the ECM as well.
If you don't have the right voltages at the pedal, then you are looking at the supply and grounds to the pedal.
It is interesting to note that each sensor is given a different supply and ground source (possibly to overcome a single failure point scenario)
Pedal plug PA1 (6 pin)
Pin 1 = Variable output from sensor 2
Pin 2 = 5 volt supply to sensor 1
Pin 3 = Ground to sensor 2
Pin 4 = Variable output from Sensor 1
Pin 5 = 5 volt supply to sensor 2
Pin 6 = Ground to sensor 1
If pedal voltages are swinging through the proper ranges, we will next explore the TPS feedback voltages.
TPS plug EN13 has 4 pins.
Pin 1 = Ground
Pin 2 = TP2 variable output (1.65 volts at idle, 4.2 volts at full throttle)
Pin 3 = TP1 variable output (0.74 volts at idle, 3.97 volts at full throttle)
Pin 4 = 5 volt supply
If the throttle body is not fully opening, then you should not be seeing the higher end of the voltages at pin 2 and 3. only if the throttle body is opening fully should you be seeing around 3.5 to 4 volts coming out on those two pins.
I hope this is helping.....let us know what test results you get.
Yesterday I run into a snag on the Suburban I'm working on delaying a needed gasket until today, so I went to the Jag and I had read about doing "hard reset" of computer, and a good friend had told me that meant disconnecting the harness from the computer and reconnecting. Since I had already disconnected doing the previous tests, I thought I should start it and see if that made a difference. It started and responded to the pedal and revved as commanded. My son was working on another vehicle blocking a test drive, so I waited until this morning, today I started to test drive, but it had already went back to limp mode. I have to go put the Suburban back together, then I can go back to following your tests. I thought maybe that information might mean something to you, so I'll check back before I begin the tests. Thank you so much for all the help. Dan
I finally get a chance to take the readings and decided to check TPS readings first since they are easier to get to. All 4 readings are correct (including the ground at pin 1). If I understand what I'm reading into this shouldn't the pedal outputs be OK since throttle opens wide and TPS voltages are right? Or am I missing something?
I cleared the codes before testing so throttle would open. Are there other sensors that might bring a P1229 code?
You initially reported that the throttle body would not sync.
I interpreted that description to be that the behaviour you were seeing was lack of throttle body opening when you depressed the accelerator pedal....resulting in the P1229 code.
Hence the verification of what the pedal sensor was sending out in the way of voltages to the ECM (pedal up versus mashed into the carpet), and TPS sensor feedback to ECM through range of movement.
So what is actually physically happening on your car?
Is the throttle body responding proportionally to your pedal movement, or is it not responding, or only partially opening?
Sorry for the confusion, the throttle body only opens if you clear P1229. Then it opens accordingly as pedal is depressed. After starting engine, if switch was on during test, then it's back to limp mode and doesn't open much if any. I discovered that it would open when I first plugged computer harness back in and connected battery. Then it started, revved as normal. but after shut down, then next time you start it, you get P1229 and limp.
I should maybe tell you that I bought this car from a garage who had tried to fix it for the lady. They had a nice scan tool, but everything in their shop was more common makes, and he replaced the throttle body, the pedal assembly, the crankshaft sensor, and I don't know what else. He's the one who said it wouldn't sync, but couldn't go beyond that. Having sold auto parts for 50 years, I've played with lots of cars including computer equipped, but this is my first Jag and my wife fell in love with it. 117000 miles, and well kept. Hoping to get it straight before Christmas.
Thanks for helping so much. I probably wouldn't have gotten this far without your help.
Mostly a GM man but have owned many different brands.
So the test (according to diagnostics) is to roll ignition to run position and then slowly depress accelerator to floor over a 5 second period and slowly release, repeat 3 times.
If throttle body tracking is ofailing you will get a MIL light (check engine) which could be orange or red and a P1229 error.
I haven't fully understood the part you mention about "after starting engine, if switch was on during test, then it is back to limp mode".....what switch are you referring to in this comment?
Throttle position might be marginally affected by some other sensor inputs once the engine is running, but with it not started and ignition switch just in run position, any of those inputs will be nulled.
Most of the other sensory inputs will modulate injection not throttle body position, and you are not seeing other errors from MAP, MAF or O2 sensors.
What can be a gift that keeps on confusing are suspect relays, as the contacts can be pitted or tainted and have occasional resistance variability. Have you swapped out R11 (Throttle motor relay) just in case there is some instability of resistance? You could probably locate a identical relay in the fuse box that is doing another function you could swap over as a test.
I don't see it being another sensor without you getting alternative error codes being flagged.
I meant if ignition was on while reading voltages, then when you turn it back on to start, it has already gone to limp mode. the first time after clearing the P1229, the throttle will open wide, but regardless of whether you start it then or turn off and back on it will be in limp. I have swapped relays at least once, myself and believe they tried that previously at the garage I bought it through. I have tried the 5 second part a few times, but in afterthought, I'm not sure if codes were clear when I did, so I will do that next, I guess. The only other error code I got was when I forgot to reconnect MAF sensor, and I cleared it right away. There is a P1000, but I'm told that means I'm reading the codes.
Do you happen to know if the throttle body replacement was a brand new part or a second hand part?
I can't think of anything else that would interfere with throttle motor movement, virtual or otherwise. I am assuming the throttle spindle and butterfly are not actually binding or jamming through their range of movement?
It is a bit like a basic remote control system.......you have your joystick input (throttle pedal), the interpretive circuit and transmitter (ECM) and the servo motor (throttle motor).
The interpretive circuit is effectively just comparing the resistance inputs from the throttle pedal and making sure the throttle motor obeys ....the only reference feedback it can get to do that is the throttle position sensor (TPS).
So if the pedal input to the ECM is not being met by the appropriate feedback from the TPS, the ECM assumes the throttle motor is at fault or the TPS is not giving proper readings.
If the TPS were sending back dubious info to the ECM due to a failed resistive track in the TPS (they have two resistor tracks inside, the same as the pedal sensor) then I would expect you to be getting P0121 or P0123 errors.
Peaked my interest regarding the origin and integrity of the throttle body that was fitted to your car.
DC motors get brush wear and worn and scored armature contacts with age, which can lead to weak or dead spots in their rotation.
You might be able to bench test the throttle motor operation if you have access to a variable DC regulated power supply that will give you the ability to quietly sweep the voltage from 0-12 volts.
One that has current limiting and a current meter display so you can observe if the current has any spikes or dips as you gradually adjust the voltage.
The greater the DC voltage applied to the motor terminals the more it will overcome the spring return force that returns the butterfly back to the resting position.
The motor is coupled through reduction gears to the spindle, but effectively it spends most of its time in a relatively stalled position as the throttle is not always moving but is always working against the spring.
TB is new, and if I clear code and remove intake hose I can watch throttle plate open and close normally. after starting engine it reverts back to limp and doesn't open. when I took readings at TPS, voltages on both outputs read normal according to the specs you gave me. I am going to clear code again, and do the 5 second thing again, since I'm not sure code was cleared when I did it the other times. Ill let you know...
OK, I made sure there were no codes, performed throttle procedure, started engine revved it(not extremely about 3500 to 4000) a few times then suddenly when at idle, idle sped up slightly, red circle with exclamation point in middle came on, MIL did not, went back to limp. Reread codes and got P1229 again. When it sped up normal 3 or 4 times
I thought finally I did it, and that was when it went back to limp. Sometimes you just can't win.
