Gen2RX

Hi everyone, I’ve been dealing with an immobilizer issue for the past few months that’s been driving me crazy and I finally decided to post here because I want to see what the community thinks before I try anything else. I’ve scoured the internet looking for immobilizer information and similar issues but haven’t found anything that’s helped. I’ve done all sorts of repair work and have access to decent resources so I’m ready for any ideas you have. Thank you for helping me!

Quick bullet point summary:

• Sudden crank no-start after months of trouble-free use
• Replaced fuel pump after checking relays and fuses but did not verify operation of the old pump
• Able to drive to and from work once then crank no start again
• Spent more time diagnosing and determined it is an immobilizer issue by noticing that the security light still flashes steadily with the key in (I was not paying attention before the fuel pump replacement)
• Brought to the dealer and they found code B2784 open/short key transponder
• Replace key transponder
• Able to start
• I replaced the battery when picking it up from the dealer and the same crank no-start immobilizer issue reappeared
• The B2784 code is back and cannot be cleared with the Techstream
• Attempt the OBD port jumper immo box pairing procedure for 30 minutes
• Same crank no start issue, Techstream not autoconfiguring when connected (possibly normal operation because it’s an older car)
• The dealer claims to have tested the immo box behind the blower fan and claims it tested fine but I don’t know their method
• Try waiting longer than 30 minutes for the OBD pairing procedure
• Able to start multiple times over multiple days to ensure the problem is resolved
• The same crank no-start issue is back after coming to pick the car up
• They recommend replacing the main ECU
• Replaced the main ECU myself
• Still has the same immobilizer issue crank no start, security light flashes with the key in

The longer version:
I bought this car used with 236k miles on it from a friend about a year ago and have had a completely trouble-free experience until this issue. I was refreshing everything, changing the suspension, and replacing the oil cooler lines. A few months ago at 241k miles, it had a sudden crank no-start issue that I guessed to be the fuel pump. I was able to replace the pump and start the car directly after and drive it to and from work once before the crank no-start issue came back. I verified the fuel pump was running while cranking this time and searched for other potential issues and noticed that the dash security light acts like it doesn’t recognize the key by continually flashing even after insertion. Before replacing the fuel pump I wasn’t paying attention to the security light so I’m not sure if it was the initial issue. The key can still remotely unlock the doors but I am aware this is a separate system. After letting the car sit for around 9 days it was able to start again and drive to and from work where it then had the same crank no-start immobilizer issue.

I brought it to the dealer because they have the tech stream and I thought more experience. They found code B2784 meaning open/short in the key transponder which my reader couldn’t detect. They replaced the transponder and were able to crank and start successfully but when I arrived to pick up the car I changed the battery for a new one and the same immobilizer crank no start issue came back. We then tried the Christmas tree dash OBD port jumper immo box pairing ritual for 30 minutes but still no luck. When connecting the Techstream we had to manually select the year make model because it wasn’t auto-detecting though I’ve heard this can be the case even when everything is properly functioning since it is an older car. They claim to have tested the immo box behind the blower fan and said it tested as functioning properly but I’m not sure of their test method. They then tried OBD jumper pairing for longer than 30 min and were able to crank multiple times over a few days but when I went to pick it up the crank no-start issue was back.

They recommended replacing the main ECU. Since I was paying dealer rates for no progress I took the car back. I swapped the main ECU on my own and waited 45 minutes during the OBD jumper pairing ritual and it still has the same crank no start security light still flashing issue. The next steps I'm guessing are to check every electrical connection that relates to the immobilizer. Possibly a bad certification ECU? I find it strange that the issue comes and goes seemingly when it wants to.

At this point, I’m okay with disabling the immobilizer since it has caused me such a headache. PM me if you can advise on that.

Overall the car is in good health and leak free so I really don’t want this to be the reason it gets scrapped or parted out. Thank you for any help or thoughts! Even a good luck comment at this point

Mesquite77

Two cents, water intrusion or a bad wire, connector.

When it cranks, no start have you tried turning on ignition, and leave it on a few minutes before attempting crank? I.e., this sends some current and warms up ECU and their connectors a bit, and possibly drying out modules. Was the fix for mine, happened once years ago, gl.

Mesquite77

From 2008 RX350 SM, immobilizer wiring diag:

Margate330

Hi Gen2RX,

Welcome to Club Lexus and your 1st Post!

A year or two ago I did a deep dive on the Immobilizer system just for fun.

Fair warning, it's a little deep for DIY but has lots of info on how it actually works and maybe you will find a clue.

Link: https://www.clublexus.com/forums/rx-...a-signals.html


Other links:

Link: https://www.clublexus.com/forums/rx-...xperiment.html

Link: https://www.clublexus.com/forums/rx-...rm-thread.html

Gen2RX

There was a lot of rain before this issue so that's a good idea. I tried all sorts of weird things initially including leaving the ignition on but I'll charge up the battery and give it a shot again!

Gen2RX

Thanks Margate!

I really appreciate all the work you put into making those threads. I saw them when I was initially troubleshooting before I had an account here but I'll read through them again and take more notes. I've done similar low-level computer work before so I just need to spend the time verifying everything.

Margate330

Knowing how the system works this would be my best guess on where to begin.

The clue is in the intermittent nature, there may be a pattern.

All else fails, it's the dealer for service or start digging in the wiring and trace everything out. Lol

Fun Fun! Haha 😂

PS- if the dealer won't work on it and nobody else will either, I'd start with the Immo Box relocate. I did a thread on this in one of the links. This will let you confirm the Immo Box aka the immobilizer ecu is getting power when the key goes in because it will be relocated where you can have access to the pins and wires.

Mesquite77

>>>> There was a lot of rain before this issue so that's a good idea

Yes, in my case it had rained all night, and the plenum was packed full of leaves, which I suspect diverted water away from the drains.