If your Lexus GS 400 is not starting at all, there are several possibilities for this condition. Trying to jump-start the vehicle will generally rule out a bad battery or a faulty alternator. Also, be sure to inspect the battery, to determine if any of the connections are corroded or loose, which may also explain why the GS 400 is not starting. However, if you can rule out these possibilities, then chances are that it is the starter that needs replacing.
Remove both battery cables from your Lexus car battery. By doing this, you will disengage the engine's cooling fan, which has the potential to start up even while the GS 400 is turned off. Wait at least 15 minutes after disengaging the negative battery cable before taking any other steps.
Remove the manifold cover, which is located in the middle of the engine, by using a socket wrench. There are four bolts on top of the manifold cover, securing it to the upper plenum.
Remove the top half of the air filter casing with a screwdriver. Unscrew the clamp that holds the main intake hose, which connects to the center of the manifold. Remove the main intake hose and put it in a place where it will not get dirty. If the air filter is dirty, then you should replace that as well, since it will improve your GS 400's gas mileage and performance.
Use a socket wrench to remove the 22 bolts that connect the upper plenum to the lower plenum. You may need to use a torque wrench on any bolts that are too tight for removing with an ordinary socket wrench. Once the upper plenum is removed, place all of the bolts in their holes on the upper plenum, so that you will not lose track of where each bolt fits. Use shop cloths to cover exposed holes and gaskets of the lower plenum so that dirt or debris does not fall into the manifold, which can cause serious damage to your Lexus GS 400's engine.
Use a socket wrench or torque wrench to remove the two starter bolts. Disconnect the white electrical tab that connects the starter to the Lexus GS 400's electrical system.
Install your replacement starter into the manifold-starter compartment of the Lexus GS 400 and tighten the starter bolts with a socket wrench. If you notice that the bolts are difficult to tighten, then you may not have aligned the starter properly with the transmission's flywheel. Remove the bolts and re-insert the starter. Reclip the electrical tab that connects the starter to the car's electrical system.
Use a socket wrench to reinstall the upper plenum, making sure that all bolts are tightened. Replace the negative and positive battery cables on the battery terminals and try cranking the Lexus GS 400. If it still does not start, then you may have improperly aligned the starter with the transmission's flywheel, in which case the plenum and starter need to be removed again and reinstalled. Once you have successfully started your Lexus, turn the car off and reinstall the air filter cover and manifold cover.
