az-dave

Tuanville -

Can you repeat a brief run-down of the things you've done so far?

Have you had your YAW sensor checked? It is supposed to detect when the car is sliding, and then Cuts power to the TB to get traction again, but if its sending a bad signal to the ECU and ABS/VSC module, the ABS/VSC module will incorrectly cut power to the TB, which puts the car into Limp mode. I dont know if this forces a code P1120 & 1121, but it might.

98GS300UGH

Hey Everyone, this forum rocks!

So I read all the possible causes for a p1120/p1121 and the CEL, and VSC light and limp mode which is happening to my car and I'm about to purchase the lever assembly. But before doing so I wanted to unplug the wire going to the pedal sensor on the lever assembly to see if maybe it was a loose connection or corroded and the small tab that locks the wire end into place broke (I didn't realize there is a clip you press so I kinda wiggled it out and then it broke one leg of the locking clip... in my own defense I was working in the dark with very little light on the back of the plug) So my first question is, how can I get a new end for the wire? Do they sell the end or do I need the whole wire? My second question is, I noticed a squeaking noise coming from the driver's side rear wheel that sounds like a brake sensor squeak, and it's more noticeable in reverse... the noise comes and goes when moving forward. So I read something about the ABS or VSC sensor at the wheel? Could this be causing the codes and limp mode? I know it's unlikely since the codes specifically point to the pedal sensor, but I was wondering if it's a possible cause. I'm kinda bummed-out about the wire end even though it still fits snugly it will pull off easily. Hopefully I can get a new one on easily or I maybe have to wire tie it or tape it on??

Thanks in advance for all your help! My car is sitting in the driveway til this is resolved

az-dave

98GS300UGH:

Ive managed to break all the retainer tabs on my TB also, being very careful (Toyota retainer clips are very stubborn)...and for 3-4 years they are tight enough to stay on never came off once...I wouldnt worry about them.

I dont believe your hearing an Anti-Lock brake sensor squeak...the AB sensors are actually deep within the Hub where the wheel bearings are pressed in, and they dont come close to contacting anything. The sensor itself is nothing more than a magnet with wire coil around it that picks up a magnetic pulse as the hub turns, on the hub inside the bearing area is a machined "sprocket" with teeth on it, each tooth causes a magnetic pulse inside the sensor.

Your squeak is most likely the wear tab on the brake pad touching the rotor, or you may have a sticky brake caliper piston letting the brake pad maintain contact with the rotor (both bad)

98GS300UGH

AZ-Dave thanks for your response! I found the lever assembly thru Toyota and the owner of the dealership owes me a favor so they're getting it for me at cost for $205.

Is it safe to assume with the p1120 and p1121 and the symptoms I'm having that this is the fix? I really don't have the skills to test the components and the dealership doesn't even know what I'm talking about and they say they haven't seen this car in years and that scares me and sounds like big bucks for them to diagnose what we already know. So if the code is pointing to the pedal sensor and the pedal sensor comes on the lever assembly, then it must be the the right part for the fix correct? Am I taking a risk here by assuming it's the lever assembly? The car will sometimes leave limp mode after a restart but always goes back to limp mode within a few minutes. It's funny because for almost a year the car was giving me a slight pause intermittently (almost like a dead-spot somewhere in the pedal travel) when I'd hit the pedal, and I had no idea what it was... I guess the sensor was on its way out. Please advise if you think this is NOT the right approach to the fix. Thanks!!

az-dave

Yes, your taking a risk, unfortunately those codes get thrown if the Throttle Control Motor, TPS, or ABS/VSC module are bad, and possibly the YAW sensor. The deal is, Lexus Dealerships take the SAME approach in repair, they replace the TPS first, if that doesnt fix it, they replace the entire TB, if that doesnt fix it they suggest new ECU, if that doesnt they suggest ABS/VSC module.

Here are your potential problems - in order of most likely/easiest/cheapest to most difficult/expensive.
1) TPS throttle Position Sensor - front of TB, not to be confused with Lever Assy.
2) Lever Assy/Accel Pedal Sensor - back of TB - 4 screws, attaches to throttle cable.
3) Throttle/Idel Control Motor - front of TB pass side.
4) Mechanical prob/stick throttle valve shaft in TB itself.
5) Bad Wires between any sensors and ECU and ABS/VSC module
6) bad ABS/VSC module on Master Cylinder
7) Yaw Sensor malfunction or bad signal or bad wire.
8) ECU
9) Combo of above.

Lexus wont do anything different than above except after doing the TPS, they will ONLY replace an entire TB rather than the lever assy or control motor, then they move on to the other items. I know...I asked 3 dealers. Its kinda lame. Same type of diagnosing when my master brake cylinder booster went bad...they couldnt diagnose it properly. Brakes went 100% out after getting car from 2nd dealer who replaced a fuse and battery terminals...nice...almost crashed...good thing emergency brake worked. That was 6 years ago...I dont go to dealers anymore needless to say.

98GS300UGH

Thanks az-dave. But the more I read the more I see people saying the TPS is not the usual suspect here and it's more than likely the lever assembly. I think it may have been you, not sure, who said the TPS rarely goes bad and it's more often the lever assembly. Also, when talking to the dealer I found the same thing you did, which is they just change the entire TB, which in most cases is probably the lever sensor which is the bad component. The way I see it, for $205, it's a great deal on the part and if I had to pay to diagnose the problem I would pay a lot more than the cost of the TPS if it ends up being that... then of course it could be the motor... Ugh. I'm surprised they go as far as to wire the car with sensors to each part yet they all trip the same code. Why would the code then specifically mention the "pedal sensor" part on the TB? Aren't there different codes for the motor and TPS???? I'm a little disappointed in the engineers at Lexus!

Just read a different forum and it seems there are specific codes as follows:

PO120: TPS
PO121: TPS

P1120: APPS
P1121: APPS

az-dave

98GS - Ahhh...and thus the creation of this thread.

Its obviously a flaw in the way the codes are stored in the ECU. This may be designed intentional, or a real error. In any case everyone appears to get the same 2 codes and the Lexus repair book procedures which the dealers are required to adhere to, require the TPS first, then entire TB.

As for why a bad ABS/VSC unit or Yaw sensor can cause the same codes seems like a design error to me, or it could be that the description for those codes is just over-simplified, and those codes really refer a problem in the entire TB/TPS/LeverAssy/Motor Control/ABS/VSC system (in other words the code description may be incomplete)

As for the TPS being bad - Ive found most people replace it, and no fix, me included. I took mine back to Lexus and forced them to return it because I paid them $135 to diagnose the problem, got the read-out, and bought the part based on their report stating "Replace TPS Sensor"...they kinda backed themselves into a corner on that, and they reluctantly refunded my money and then told me I needed to buy an entire TB because the rest of the sensors were "non-user serviceable" and claimed "The ECU wont recognize the parts unless the entire TB is replaced and the ECU reprogrammed) - A Bald-Faced Lie...that was the last time I ever had Lexus Try to Diagnose a problem for me. (when I called other Lexus dealerships they said that was the case as well)

The Other option I highly suggest is to buy a used TB off Ebay off a 2002-2005 GS as a back-up. You can use the Control Motor off of it as well. They run between $300-$400. I think got mine from GreanLeaf Auto.

Hope this thread helps you out, please keep us informed what happened and what you end up doing that fixes it.

98GS300UGH

Will do, thanks! Wish me luck!

vlogs300

hey guys i had the same thing just a couple of hours ago. but my check engine light was on as well. i havent went to go to diagnose it yet but i will tomorrow..do you guys know why the check engine light is on too?

az-dave

Go to the very first post of this thread for your answer.

Then read every post for additional troubleshooting and other good stuff and answers.

ihiryu

iTrader: (7)

(sigh) I've replaced; lever assembly, TPS, APPS, it worked well for a day or so, then the lights came back on. I'm ready to sell this POS.

Does anyone have a wiring diagram?

az-dave

Tuanville posted wiring diags, which I re-linked to last week. check a few posts back.

ihiryu: the Lever Assy and APPS are the same thing. Did you replace the throttle control motor?

Also, this may also be caused from a problem with ABS/VSC module and possibly YAW sensor, or with the actual mechanical TB itself.

Did you try swapping out the entire TB yet?

ihiryu

iTrader: (7)

Sorry I meant the motor. I also replaced the entire TB. Do you know if there's any way to test the ABS module, and where is the YAW sensor located?

az-dave

- I just remembered - Have you checked the ABS and VSC relays? They are located in the Fuse/Relay box on the drivers side under the hood next to the master cylinder.

Make sure they are not bad...If the VSC or ABS relay is bad it can force the car into limp mode.

No way to test the ABS/VSC module that I know of, it has the full ability to cut entire throttle response.

If you have replaced the entire TB, and your still in Limp mode, then something is telling the car to go in limp mode, which is controlled thru the ABS/VSC Module.

I do not know where the YAW sensor is, is could be inside the ABS module for all I know or somewhere on the Chasis, Im sorry I dont know. I actually just discovered the YAW sensor issue a few days ago when researching trying to find wiring diagrams. I didnt look into it very far, except it affects mostly 98 and 99 models.

Im still not convinced you dont have a wire problem...have you testing the wires to the Motor, APPS and TPS?

I dont believe its your ECU, thats just my feeling though. I think its in your wires/pins, the ABS/VSC or Yaw sensor.

If youve replaced everything on the TB, then it leaves you with only those other options, the ECU being the absolutely last thing (requires reprogramming of keys to start motor).

Have you taken to a lexus dealer and told them the entire TB has been replaced? I know I dislike and distrust the dealers, but once you tell them your 100% sure its not the actual TB itself, you may actually get them to read the codes and diagnose the problem for the $135 diagnosis fee.

At this point...tongue in check, I actually suggest a dealer to diagnose...you might find an honest mechanic since he knows he cant BS you on the TB or TPS sensor.

ihiryu

iTrader: (7)

I have not, I took a look at the relays and they look good, I never tested them though. But here's the thing, if I clear the code, it'll run for a few days (or minutes) without the code. Then it'll come up randomly.

I found the ABS/VSC ecu and the yaw sensor for 115, but it's a 2001 do you think it's compatible?