Hi,

My 1999 RX300 began to experience engine start failure a few weeks ago. Jumping always help. Changed new battery, problem persist. A free battery diagnostic shows the new battery and the charging system are both fully operational. My further investigation shows a predictable pattern:

1. I can do either one of the following to make the car start after failure:

1a. Remove and re-attach battery and wait for 2 minutes; or
1b. Remove and re-attach the 10 Amp fuse labeled "Dome" and wait 2 minutes; or;
1c. Jump the car with another idling car; or
1d. Recharge the battery (the charger will indicate fully charged in just 2 minutes or less).

2. After the car is started, I can drive it as much as I want, as far as I want.

3. Once I turn off the car, if I try to start it immediately, it will start without a problem.

4. If I leave the car off for may be 5 minutes or more, it will fail to start. I can hear the engine cranks, but no indication of engine firing at all.

Method 1a and 1b seem to suggest that either the ECU or the immobilizer is picking up wrong sensor reading. Method 1c and 1d suggest that a higher charging voltage was able to bring the car out of the fail state. Method 1d also confirms that the battery is not the cause.

My question is, does anyone have experience with the immobilizer system of RX300 (where are all the sensor, etc.)? I doubt it is the ECU's fault, because the car runs fine after it is started.

Thank you

--Michael

 

Q: In your judgement, does the engine spin as fast when it catches as compared to when it does not catch?

Q: Have you tried with another key (second master or valet)?

The imob sensor is pretty close to the ignition switch. Also remove all other keys in the key ring to eliminate interference issue.

Also turn off the auto (if set) head light on.

Salim

 

Hmmm perhaps try changing the battery in ur KeyRemote. In order for the engine to start it needs battery in the transponder for it to deactivate the engine immobilizer. The engine will crank but it wont start. So it could be the battery in ur key transponder

 

To answer salimshah's two questions:

Q: In your judgement, does the engine spin as fast when it catches as compared to when it does not catch?
A: The engine spins just the same way in either cases (fail or successful start).

Q: Have you tried with another key (second master or valet)?
A: Yes, I tried both master keys, and I will try the valet key today.

However, I don't think the key is the issue. If your key battery is dead or taken out intentionally, you can still open the door manually and start the car, just as it would with the valet key, which is a passive key with no battery.

Some insight from some one who has worked on the immobilizer system would be helpful and appreciated.

Thanks

--Michael

 

As you already know, your problem is not what I would call run of the mill problem.

Charging or jump just gives you a possible boost in voltage (assuming your battery is still in good zone).

Disconnecting the Dome circuit has load (battery side) and reset (dome ckt side) implications. 1st is back to battery peak level and second could be related to imob sensor or ecu of your vehicle. I dont have a ckt diagram to trace this.

So where can you get help from. Most probable is Lexus dealership. They again may resort to swap things instead of detailed debug-fix. Nothing wrong with approach with increased labor charge.

I would reset the ECU (remove battery power for 45 min). I wish I could help you more.

Do let us know how you eventually fixed the problem.

Salim

 

Have you measured the current drain on the battery with the engine off?