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You can't start a fire without a spark

My wife drives a 2001 LX470 - in Feb 2008 the key would not turn, we replaced a loked cylinder. In August the key would turn, the starter would turn, the car would not start - when faced with the choice of a new ignition system (~$1500) or a possible fix of a new transponder key amplifier ($200 non-refundable) we went the the transponder key amplifier - it worked! However on Saturday (3/7/09) the key turned, the starter turned, the car did not start…any ideas othert than what we have previously explored?

There is plenty on the web about GM’s security systems,look and see what someone has already written about your car,start googling.

Thanks but this is not a GM vehicle - it is a Lexus LX470. However I will check out any Lexus sites.

When you turn the ignition switch to START, the voltage goes to the neutral safety switch, leaves through the P or N contact, goes to a junction and splits three ways. One wire goes to the starter solenoid, one to the engine computer, and one to the instrument cluster.
As you are cranking the engine, there should be an indicator lamp that lights in the instrument cluster. This light indicates that the START voltage has gotten to the junction. If the engine cranks, this light would be a redundant indicator of power to the junction.
The third branch, to the engine computer, should be checked that the START voltage actually gets to the engine computer. The computer decides whether to empower spark and fuel flow.
When you crank the engine, check for spark and fuel. If neither, you need an able mechanic. Besides a good repair garage/mechanic, try an automotive Security and Alarm Service. They may know have more expertise than the others (and, be cheaper).

Thanks - will contact a local auto alarm/remote start service a friend recommends.

It looks like your ignition switch carries high electrical load (like Hondas). This load (current) can burn contacts, over time, in the ignition switch. The fuel injectors get their power directly from the ignition switch. If the ignition switch contacts are burned, there will not be power (12 volts on the black/red wire) to the fuel injectors. Check for 12 volts, at the fuel injectors with the ignition switch in ON (engine not running). If there is no power (12 volts) at the fuel injectors, check back to the ignition switch.

Ignition switch (not ignition lock): http://www.autozone.com/R,1702936/vehicleId,2641701/initialAction,partProductDetail/store,1140/partType,00189/shopping/partProductDetail.htm

That was the idea I was trying to send you. If info is available for one brand car it stands to reason its there for others. Why should I do someone elses googling?

Well, today I tried it one last time before calling the tow truck - it started! I drove it around, turned it off and started it up again many times. Faulty wiring? Bad connections?

Ignition switches, as well as other switches, can be intermittent in that way. It may happen again; and, we’ve been over that.