bobsmith99

Got a weird problem with 2004 LS430.
Suddenly when start the car, it give several beeps and started, and it give beep-beep sound, wait several seconds then double beep again. Connect techstream, it show code B2799 which means communication error between ECM and immobilizer ECU (however, no check light on dash board).


Here is the B2799 description copied from repair manual:

This DTC is output when:
1) the ECM detects errors in its own communications with the transponder key ECU;
2) the ECM detects errors in the communication lines; and
3) the ECU communication ID between the transponder key ECU and the ECM are different and an engine start is attempted.

Before troubleshooting for this DTC, make sure no transponder key ECU DTCs are present. If the transponder key ECU has a code related DTC, repair it first.

DTC No. DTC Detection Condition
B2799 Error in communication between ECM and transponder key ECU, and in communication line Communication ID is different during communication with transponder key ECU

Trouble Area

Wire harness
ECM

The weird thing is that the car can be started and driven without problem (except the annoying beep-beep sound). Before the B2799 code developed, there was a problem that the car can not be started if the key is not remove from key hole and inserted again (start the car then turn key to off position without taking the key out, try turn to start position won't start the car.).

Does anyone has experience with this? Maybe a slowly dead immobilizer ECU? I don't think wire could get any problem since there is no water problem for the car.

Thanks.

LeX2K

That is a strange problem.
Maybe, I recall seeing a couple of threads here (or maybe another forum) where the immobilizer box went bad. I wonder if the key sense switch is flaky causing module confusion, put in key sense signal goes up and down transponder is seeing the key but the key sense switch isn't.

911LE

If the car runs it's not issue #3 on the list. If the incorrect id is used the engine will start but immediately shut off. You could try the immobilizer relearn procedure to see if it changes anything.

bobsmith99

Today I hooked techstream and got the live data list of immobilizer. Please see image:


The thing I can not understand is that the "Permit(Start)" value is OK, that means the car can be started, but "immobilizer" value is "Unset", "Unset" seems that the immobilizer can not recognize the key. How could it happen? Those values won't change even after the car been started.

I tried to add a new key, but stuck at the first step (remove and insert key and turn to ON position). Please see images:




Please see the pictures and give some ideas.

Thanks.