I have a 1994 LS400. Recently, the TRAC light and Check Engine light come on together once a while when I first start the car in the morning. After the car warmed up, if I shut off the engine and start the car again, no lights come on, everything would be fine. I noticed that this problem gets more profund when the temperature drops.

I run the diagnostics (with help from the posts of this forum), I got the error code 41. Which tells "TP Sensor Signal " from the web page of troublecodes.net.

What is TP Sensor? What could be the cause of the error code 41.

Thanks in advance to anyone's help.

 

The throttle position sensor (TPS) is in need of replacement. I can't tell you where it is in your car since I own a 1994 GS300, but I can tell you that my new TPS was about $110.

 

How many throttle position sensors does 1994 LS400 have? I have read some of the posts sayting two throttle position sensors. If indeed the car have two sensors, for the error code 41, how do I know which one is bad to replace?

 

Hello,
You have only ONE TPS on the engine. This sensor moves proportionally to the throttle cable when the accelerator pedal is depressed.

The TPS converts the angle the throttle plate is opened to a voltage that is read by the computer. It uses this voltage to send the correct amount of fuel into the engine. This fuel corresponds to the amount of air coming in to the engine through the open butterfly plate on the throttle body.

To find the TPS, remove the plastic center engine cover, and locate the throttle body. You can find that by following the large black hose coming from the air filter to the engine. Remove this hose, and you should see a metal plate that is closed, which does not allow air to enter the throttle body.

On one side to the throttle body, there will be a throttle cable assembly coming from the accelerator pedal in the car. If youmove this cable, the throttle plate will open and then close when the cable is released.

On the OTHER sideof the throttle body is the TPS. It is bolted to the throttle body, but the inside of the assembly is connected by means of a blade or spline that corresponds to the throttle plate. The inside of the TPS houses a small resistor that moves as the plate open. On the outside of the TPS is a connector and wire assembly. If you are planning to change the TPS right away, remove the wire assembly connector from the TPS. It will only go on ONE Way.

USE CARE REMOVING THE TPS FROM THE THROTTLE BODY. Some TPS have EXACT holes on the body of the unit, meaning that there is no adjustment for the TPS...just align the blade on the throttle body when installing the new TPS, and install the bolts, connect the wires, and the job is done.

HOWEVER, if the body of the TPS has ELOGATED holes on the mounting bolts, then use extreme caution when removing and installing the TPS. In fact, MARK the holes by scribing a line on the plastic body where the holes wil line up. do this BEFORE removing the old TPS.

Install the new TPS in the exact same position as the old unit, and move the throttle plate back and forth to insure there is no binding. Then connect the wiring, start the engine, and check for smoothness.

It may take a few drives to allow the computer the time to orient the new TPS to the system. IF you had a check engine light, use a scanner tool to erase the code stored in the computer. If you do npot have a scanner, or cannot get to one, just understand that the check engine light will go off after a few days. This is to allow the vehicle the chance to accumulate the required number of starts and stops during normal driving.

Each time the car is started, warmed sufficiently, driven long enough to heat the car to operating temperature, then parked and allowed to cool, completes one cycle. The engine will have to cool down completely before starting cycle 2. This will continue until the computer is satisfied that the TPS has been fixed. Then the computer will turn the light off.

I hope this will help you in some way. Please contact us collectively, or use my private message (pm) and contact me privately.

Good luck,

 

GSEREP1,

Thank you so much! Your reply is so thorough and detail, it is great help. Really appreciated.

 

Curious, same proceedure for a 95 ls400? From what I understand, the engine is slightly different?

 

Not sure if this pertains to 1994 but for 1993 LS400's, you can remove the EFI fuse for a few minutes. Pop it back in and the CEL should be gone.

If there are still errors, the engine light will turn back on.

Chris

 

The 94' LS400 has TWO Throttle Position Sensors.... code 41 is for the primary TPS and code 47 is the sub TPS... both are located on the front of the throttle body next to each other and are held in place with 2 Philips screws each.. Usually when both TPS fail the TRAC control light will come on and you will get a throttle cut under rapid acceleration. But the car will still drive with less than 40% throttle.

 

My '94 LS has only one, its a non-Trac model, but I get that throttle cut you are talking about. I got a code 41 also and replaced the TPS. It runs smooth now but I still only have about 40% throttle. I have been trying to figure out why since I bought the car about 6 mo ago. You are the first person to mention this throttle cut and a possible reason for it. Could it still be the TPS maybe out of adjustment or my MAF which is now unplugged? Any ideas would be greatly appreciated.

 

Wow, didn't realize how old this thread is. Sorry, I'm a newbee. When I figure out the problem I'll post the fix. By the way, love this forum, you guys are a great help and definitely have good taste in cars.

 

yeah my 94 has 2 right beside each other on the outside of the throttle body

 

I am having the same issue did you by chance ever figure the problem out?

 

Bought my 94 ls400 2 days ago. Was throwing white smoke and cutting off when accelerating. Found clublexus and learned the ps pump valve was bad and ps fluid was being sucked/pushed into the intake and throttle body? Plugging the lines and ports stopped the white smoke immediately. Assumed the ecu is bad for the second problem but had time and found the instructions for pulling codes on this OBD1 system and consequently got the 41 & 47 codes which point to the tps and sub tps sensors. Hope that solves the cut off problem. Will confirm I indeed have 2 tps sensors tomorrow morning.

 

Installed main tps sensor, reset ecu. No luck. Thought I would get an aftermarket tps first a mostplus th151 from ebay to see if the car ran right. Still hesitates. Still got code 41 & 47. Accelerates just fine on cold start then goes back to bucking if accelerating quickly. Can drive as fast as I want as long as I rev slowly pass 2k rpm.

 

Sorry for your trouble. Things are not always simple and easy. The error codes are only showing one side of the problem. As an example, a failed O2 sensor code is often caused by the air leaking problems and changing the O2 sensor doesn't fix the problem.

When the DC voltage supply to the TPS is not pure enough and swinging by the ripple/noise, your type of problem tends to occur. Check the ripple level as is explained in the FAQ page.