Lexus Troubleshooting Questions? Ask a Lexus Expert
Has the check engine light ever started to flash? Do you know how to check for codes on these older ones using the jumper wire in the diagnostic port?
When do you mean that if you unhook the battery doesn't reset the check engine light? Has the check engine light started to flash while driving? If you remove the battery cables and then reinstall them as soon as you start the engine up the check engine light comes on? Do you have the vehicle identification number available?
When you inserted the jumper wire into the terminals did the check engine light flash at all with the key in the on position? Are you certain you had the correct terminal numbers? See the attached link. Did you try it in both diagnostic ports the one under the hood and the one under the left side of the instrument panel?
Normally whenever the self-diagnostic code will not work or cause the light to not flash it is because there is a problem with the wiring to the computer the computer is messed up which is not likely or in the idle points are IDL points in the throttle position sensor are not open. Do you know how to check the IDL points in the throttle position sensor to confirm that they are in the open position?
On these older ones the computer has to see that the throttle is closed before it will run the diagnostic check. I'm not 100% certain of that's the same on this LS 400 but it's worth a shot to check it. There is no way to check to find out what's causing the check engine light to come on without getting the diagnostic system to work. The throttle position sensor is a four wire connector on the side of the throttle body. Pin number one is a brown wire that is a ground signal, pin 2 is a green wire next to it. If you disconnect electrical connector and ohm test those two pins on the idle circuit of the throttle position sensor you should have less than 100 ohms through that idle points when the throttle is closed when you just barely crack the throttle open those point should open up and your ohmmeter should show infinity or open circuit. Ideally the best way to check this is with a voltmeter. You do that by simply and carefully back probing the wire which would be the green wire and is the input to the computer. At idle with the throttle completely closed there should be less than 3 V but typically you will have less than .5 V this means throttle points are closed and the voltage being sent from the computer goes to ground. When you crack the throttle open ever so slightly the voltage should jump up to five or 12 V depending on the reference voltage. You can check the reference voltage by disconnecting a connector with the key in the on position check the voltage of the green wire pin number two. Whatever that source voltage is it should read one of throttle is opened. So in other words with the throttle closed the computer is looking for no voltage on the green wire when the connector is plugged into the throttle body, if it is not then that means the throttle points are not closing all the way.
Can you post me a picture of what you're referring to in the overall throttle body assembly? Did you find the throttle position sensor and the electrical connector?
Can you post a picture of the throttle body assembly looking at it from farther back? Did you find the TPS? I will be away from my computer for an hour or so. I will be back on this evening.
What I need you to do is find the throttle position sensor and test the voltage on the ideal circuit on the sensor as I listed did you find the connector with the color coding of the wires as I described? I don't believe this is a throttlebody issue at this point we just want to check the TPS. We need to get the diagnostic system working so we can find out what codes set in the computer.
There shouldn't be any programming involved and you should be a to get to used one they do not use immobilizer 93.
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