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1999 Ls400


billydpowell
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today, with out warning, the CEL and VSC lights came on and the car went into the "safe" slow speed mode and had no power/ get up and go. I idled it home, power steering was moaning..
got home added fluid to PS tank. was going to autozone to get codes, but car fired up like always and ran perfect.... no lights no nothing..... has anyone ever had this happen to them??

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P1120 Accelerator Pedal Position Sensor Circuit Malfunction

From other threads I've read I'm strarting to get the feeling this happens in cold weather. It happened to me when it was about 20 degrees outside. (from another thread)

Cut it off and restarted it and it cleared up. (from another thread)

fixed by shutting the car off and restarting (from another thread)

book reads: P1120 Toyota Description
Accelerator pedal position sensor is mounted on the throttle body and it has the 2 sensors to detects the accelerator position and a malfunction of the accelerator position.

The accelerator pedal position sensor is connected with the accelerator pedal by the accelerator wire and the voltage applied to the terminals VPA and VPA2 of the Engine Control Moduel (ECM) changes between 0 V and 5 V in proportion to the opening angle of the accelerator pedal.

The ECM judges the current opening angle of the accelerator pedal from these signals input from terminals VPA and VPA2 and the ECM controls the throttle motor based on these signals.
If the the P1120 code is stored, the ECM shuts down the power for the throttle motor and the magnetic clutch, and the throttle valve is fully closed by the return spring.
However, the opening angle of the throttle valve can be controlled by the accelerator pedal through the throttle cable

LOOKING FOR ANSWERS (from another thread)

MORE: There are several threads here that report about problems with a lack of acceleration when the weather is very cold.
I then found that when I heat the throttle body (on the side where the accelerator cable is attached to the accelerator pedal position sensor) with a hair dryer before starting the car, the problem does not occur.

However, there are two sensors on the throttle body: a throttle position sensor ($140 on Amazon) and an accelerator pedal position sensor ($299, only available at Toyota or Lexus).

Can I be sure that this is due to a defective accelerator pedal position sensor (PPS)?

any comments as to what I should do? my wife drives this one.... THANKS, BP

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My 98 GS400 did the same thing a few years back. Suddenly went into limp home mode, no throttle response at all. Idled normally. The dealer found a code that identified the ECM as the problem, but as the car was running normally after a few restarts before I even took it to them, they didn't believe the code.

Another mechanic, whom I respect, stated that if the alternator had produced a voltage spike the sensors would have gone out of range, and the ECM would have had a jolt too, perhaps producing the code and the limp mode.

It has not happened again, and the engine has run perfectly. I have seen such intermittent "anomalies" on other cars, much like restarting your computer, and there is little to do except deal with them when they come up - if they come up.

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Hmmmm...losing PS fluid. Now where have I heard this before? Oh yeah. It drips from the pump into the alternator and causes electrical problems, maybe even CEL and CHECK VSC lights on.

Randy you just turned a light on....... good work..

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Its something to look at but may not be the main issue. I would check your charging system and evaluate the age of your battery as first steps. Cold weather, such as we are having all over the country, puts more stress on those components.

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I thought the power steering pump on the later VVTI LS had been relocated away from the alternator?

It is up and to the left of the alternator but still not far enough away to keep PS fluid from entering the alternator if the leak is severe and/or the pump pulley is slinging fluid about. It may not be the issue but warrants a good look in that area to determine where the PS fluid is going.

post-41820-0-30796300-1391110648_thumb.j

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Battery is less than a year old, chg system runs at 12.7, & 12.8 with running lights and standard equip on. no leaks on floor.... PS fluid added to tank, less than 3/4 inch, and over 2 years since any had been added.

I think this was a cold weather thing.

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Yeah, Billy, that is pretty low for a proper charge. It should be closer to the 13.5-14 range as Greg stated.

Now, if you have every "power hog" on that you can find...ie: headlights, brake lights, rear defroster, heated seats(you probably don't have these in TX), then you might see 12.5V. And that is normal with everything on.

Try turning off everything except the headlights and rev to 2k RPMs. If you are still in the 12.7/8 range, start looking at that alternator. You might have lost a phase due to a blown/open diode.

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Oh no. Seriously, you used a $2 voltmeter to make the measurement, Billy? I do not feel too confident in the readings if so. At least get a $5 meter ^_^ . Then we can talk.

Actually, if you can verify the accuracy of the cheap meter with a good meter(like a Fluke) then I would be ok with the cheapy. Else, fail, back to square one.

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I know other issues can cause a CEL and VSC off warning but the only time that has happened on my 2000 LS400 when the car went into limp mode was when the throttle position sensor started to fail at about 115,000 miles.. Attached are instructions on how to test it.

sf-36.pdf

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