Too Long In My Opinion

James Technician Kentucky Posted   Latest  
1999 Lexus GS300 3.0L (2JZ-GE) 5-spd (A650E)
Security Theft / No Start

This car is diagnosed but it took me far to long and ended up figuring it out with luck so would like some thougts on how be better. And I just wanted waveform saved.

Get this Lexus they say battery has been hooked up backwards and has no communication with ECM. So I check power at ECM find couple blown fuses (ETCS and IGN) think I have it fixed easy day lets collect some money, go to start it up and no start, I go back out check powers and grounds try to start again, no dice, but I do see a security light flashing. So I check to see if communication restored with ECM, which it was and then find code B2796. This is code for no com to immobilizer. First thing I do is put the key coil tester around key and the light flashes when I turn key telling me the key coil is getting excited so the immobilizer seems to be working. I then scope the 3 wires for immob AT THE ECM, RX, TX, and code. Now service data tells me these should all be 10-14 volts with key on but as you can see in my scope captuer one signal is only 5V, this is the blue/red wire i believe is the TX line. So at this point I think we have problem with either the immobilizer which is called an amplifier or the ECM not sure how to determine which is at fault, any ideas? My only thought was find working car to compare but before I could do that the immobilizer light goes off and car starts. Couple restarts later and its crank no start again, I compare scope pattern when it starts and its exact same as before, do some more digging and I finally realize the key coil is working but it is putting out weak signal and you have to slightly pull the coil off the tumbler to get it around the key and the car starts every time. Now I'm guessing the key amplifier (immobilizer) will fix this issue as it excits the coil. But this took me way to long to figure out and it was luck that I realized the coil was the problem, and im not sure 100% if its the coil, amplifier, or key that is giving weak signal. I did check resistance on coil it was 0.3 ohm. Any help on how I could have suspected a weak coil I would love to hear as once my coil tester started flashing when I turned key I moved on from coil and it was never a second thought. Anyways if people ever need known good immobilizer waveform on Lexus 1999 GS400 here she is. And why does service info say it should be 10-14 volts but we can see its only 5V, do I still have problem. If I use LED test light on the low signal I get ground at 3.0V coming from ECM, it won't light incandescent , and the other two wires dont have any power or ground when checked with LED. 

Nollan Instructor
Nollan Default

Hope this helps.

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Bruce Owner/Technician
Bruce Default

James, FYI, the immobilizer is built into the ECM on this year model. It is possible that the IMMO EEPROM inside the PCM got damaged or scrambled with the voltage mishap. If you wind up replacing the ECM and want to go with a used one. I offer an EEPROM reset for key learning for replacement modules or all key lost situations. Dealer replaces PCM for IMMO issues and it can get expensive for a…

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