mmcd

I have a problem where occasionally the start button will not light so I can't start the car. The fault I've seen is B2799 (immobilizer). I've had a mechanic look at it and try many things. It appears to be a voltage or ECU issue.

• If the battery is fully charged (12v+) it starts, otherwise no light when brake depressed.
• The orange lead (MREL I think) to the certification ECU reads about 10v when disconnected from the ECU and 5.25v when connected
• The start light does not come on and the voltages are about the same on the orange lead. If 12v from battery is connected to orange lead for a moment everything works again

The mechanic has spent a good bit of time with Lexus tech support and they're thinking 1 or more of 3 ECUs which is a bit expensive.

Any thoughts?

Hayk

iTrader: (1)

This sounds like a serious enough electrical issue that would be very difficult to provide any insight on without being there and testing everything.

I think you’re better off continuing with the mechanic or trying another Lexus shop to give it a go. Is the mechanic that’s looking at it from a Lexus dealership?

What’s the history of your car?

mileage?
accident history (crashes, water, fire, etc)?
any rodent damage?
when did the issue begin?
how many owners in car’s history?

mmcd

The car has 113k miles on it and I'm the only owner, no accidents. A few years back rats did some chewing on the wires to the ignition coils which was repaired. The problem started less than a year ago (I don't drive the car that often). I tried all sorts of things related to syncing the key. The mechanic is not a Lexus tech but he has had extensive conversations with their tech line. Their advice is swapping out ECUs to see if the problem goes away. That's fine if you have some known goods on the shelf. There is no Lexus dealer in my area. The certification ECU seems to be the expensive one. I've been looking on the web for a wiring diagram of the involved ECUs and their locations (besides the certification ECU behind the glove box). I've seen places on the web that will repair ECUs but I wonder if they will find an intermittent.

The most curious thing is that it is an intermittent rather than a hard fault which rules out a lot of things. It is also strange to have such a fault with a digital system. On occasion there's been a current draw from the battery when the car is off.

Typically the car works fine then when you enter the ignition does not give a green or any light when the brake is depressed. The door open light is on in the dash and the key fob will lock/unlock the doors. The car will start if it is jumped or there is a charger on it. The tech has shown me when it is in failure mode, he taps the orange lead with 12v from the battery and the green ignition light goes on and the car starts.

Looking at the diagrams I have there are multiple orange wires into the certification ECU:

• VC5
• BZR (to door lock buzzer)
• SEN3 (from rear door LH key oscillator)
• SEN2 (from front door RH key oscillator)
• LIN (from LIN1 main body ECU)

nevernu

maybe this is of some use. any codes thrown?

mmcd

I have seen B2799. The SAS diagram is like what I have. They don't show wire the offpage wire groups come from or go to. The connector pinouts may be helpful, thanks.

nevernu

the manual says this about the code

nevernu

re the SAS wiring diagram wires going off page I think if you tape the pages together it shows where all the connectors eventually go

Hayk

iTrader: (1)

I suspect you have some chewed/shorted wires somewhere that are making this an intermittent issue. If you’ve had rodent damage before and the car is rarely driven, it’s likely it happened again.

mmcd

Possibly, wire damage was something the tech was checking out but didn't find anything. The rat damage was under the engine cover. The intermittent seems to have more to do with the battery voltage level and that merely touching the orange correction ECU wire with 12v fixes the issue for multiple starts.

mmcd

Thanks, I was thinking that might be the case but would have been nice if they just labeled the attached page.

mmcd

You are correct, I now have a 18 page rolled system diagram, i was able to do a little experimenting with the car:

• The battery was down to 11.97v. The orange wire from certification ECU is probably either VC5 from the ignition switch or LIN from main ECU. After touching with 12v from battery: wire has a clip now one side had 2.25v declining to 1.97 over a few minutes and11.22 on the other. When connected 7.25v. Key fob would not open doors, no ignition light on depressing brake pedal even holding fob to switch.
• Put car on charger, battery 13.18v, orange wire 2.35v and 13.21v with 8.2v combined. Ignition and door locks not reacting (no light or action).
• Held fob to switch and got beep and white light on ignition
• Minutes later got orange light and key not detected on dash
• Tried touching fob to switch again, got green light and car started but still can't lock/unlock doors or trunk
• Left car and got beeps about key missing, put fob on steering wheel and fault went away
• Double checked by leaving car with fob on steering wheel then removing it through window
• Turned off car and now fob works and engine starts. Battery charged up to 12.53 volts

Any thoughts on this strange situation?

Thanks

nevernu

sorry lost track of what the current issue is. If you can start w the fob held at the starter sw and not farther away that would indicate replace fob battery?

mmcd

Fob battery was at 2.97 volts. It appears to be related to battery voltage: if under 12 (11.97) no light. Over 13 willl recognize fob against switch then after charged awhile and stopping it will then start with key and door unlock/lock work.

Current issue is I get no lights on ignition key when brake depressed if battery is somewhat discharged (haven't found where exact level is but 11.97 is too low). When I do get it started with fob next to switch fob will not act on door locks but if I then stop and start it does.

nevernu

is the B2799 code still present;if so did you check the harness wiring resistance?

( CHECK HARNESS AND CONNECTOR (ID CODE BOX - ECM) in 12.pdf?

mmcd

No B2799 now.