Hello. Last year I finally bought my first 1999 LS400. Drove smooth, everyhting was fine until after this winter. It was standing in a parking lot, with snow on top and sometimes it was -30 Celcius. When the snow melted, I thought I Will get it going, start it, drive it a bit. Hooked the battery, it started first crank. All of a sudden, "VSC OFF", "CHECK ENG" came on. I thought, okay it must be because it was standing so long. Got it out the parking space, tried to press the gas pedal and nothing. The car moves, but just on idle. Idles high. Bangs into gears. I'm sure its some sort of a limp mode. After like two weeks I finally got OBD II scanner. Hooked it up and it showed me P0120 and C1201 codes. Okay, I thought its either APP sensor, TPS sensor or ECM. Today I watched a video when a guy troubleshooted the same issue. He said that when IGN is ON, when you pulll on the cable, the butterfly valve should open because you are imitating that you are pressing the gas pedal. And mine doesn't do that. In the end, he said that the ECU doesn't send the signal to the throttle body motor and that's why it doesn't open the butterfly valve. Also he said that some kind of " shorted throttle body components were replaced". Any ideas if I have the same issue ? I took the ECU out today, opnened it, can't see any capacitors leaking or something bad but im no electrician. Any help is appreciated. I really don't know how to solve this issue.. Thank you very much and greetings from Europe.

 

I have answers but I wonder which is the one for you. In order to narrow down, I need to get some more information from you. What happens when you push the accelerator pedal all the way down? I mean the full throttle.

 

When I pushed down on the pedal really hard, then the car would rev a little.

 

Could you read the tachometer when you pushed the pedal all the way down?

 

I didn't pay attention to that very well. But as I remember, yes. The RPMS increased on the dash as I pressed the pedal all the way. Maybe it's coincidence, but last summer my dash would randomly dimmed on itself and then after a couple of seconds brightened up again, but maybe that's another problem.

 

If the rpm reaches up to 2K rpm and never goes up beyond that, it will simply mean that ECU is setting up the limp home mode. This is mostly caused by the failing TPS. It can be confirmed measuring the out put voltage curve of it. The curve rises up in accordance with the amount how much you pushed the pedal with no glitches of the curve. The voltage should goes up smoothly.

 

So in my case its most likely the TPS sensor ? Can simple ODB scanner measure this or I will need some kind of smart multimeter to do that ? The TPS is such in a bad spot and even facing down, gonna be hard.

 

Yes, it's not easy to replace the TPS. For the confirmation, it would be the best to measure the voltage curve how the output of the TPS is obtained pushing the pedal from 0 to 100%. Once the ECU is disconnected or reset, it requires some multiple conditions to set up the code and the OBD scanner often can not get the code quickly.

 

Okay, I'll try to get the ECU plugged in and everything that I removed and try it again.

 

Hey. Sorry for late reply. In that time I've been in another country for work, just now getting back to this situation. So, in the meantime, I've checked ECU capacitors, they look okay for me. Got all the computers hooked back today. When I was abroad, ordered new TPS just in case from Japan. Today I also removed the throttle body off the car, because no way I could disconnect the pkug for the tps when its on the car. When I took the plug out, I saw one contact had green oxidized stuff on it. Probably that was my only issue, but since the TPS plug is faving down, there is no way I could have seen that and cleaned it. So Im gonna clean the contact with contact cleaner, and tomorrow (hopefully) get everything back together and try to start it and drive. Since the TB is already out, also gave it a good clean. Will report back if thay fixed my no response issue.

 

Changed the TPS sensor. Didn't help. still no response. On ignition position "ON" I cant even hear the throttle motor working. I'm lost at this point. Any suggestions what to check next? Thank you.

 

Are you getting the swinging voltage from the TPS? You also need to calibrate it as is explained here.

 

Didn't check that. Will try it I guess. I just put the new sensor in the same place where the original was. Could it still throw check engine and throttle codes because it is not calibrated? Shouldn't it detect it so the gas pedal works atleast a bit? Strange that with everything connected and in place, the car doesn't see it

 

I need to know the swinging voltage to judge. Without it I would have no idea to proceed.

 

Hey. I got two pictures from diagnostic tool. Since its not mine, I got ti play with it for an hour. Haven't calibrated the TPS yet. Can you comment something on this? Does the ECM even see the TPS? Attaching 2 pictures. Thanks very much.