2007 ES intermittent start failure

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Mar 24, 2022 | 02:17 PM

#16

mmcd

Thread Starter

10th Gear

Joined: Mar 2022

Posts: 13

Likes: 0

From: wa

Quote:

Originally Posted by 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

Additional data: I could use the fob to lock/unlock the doors today but the ignition light would not come on even with the key next to the switch. Wouldn't this imply that the certification and code ID ECU are working? The battery voltage was down to 12.08v. I got a reading of 5.4v on the orange lead, 11.1v. on one side and 1.19v on the other. Car will start if battery is at 12.53v but no light if 12.08v and loses key recognition by 11.97.

Mar 25, 2022 | 08:47 AM

#17

nevernu

Instructor

Joined: Jan 2011

Posts: 1,080

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From: Ontario, Canada

The solution lies in one of these! I'll leave it to the student to complete the proof...

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16.pdf (137.9 KB, 93 views)

Mar 8, 2026 | 03:57 PM

#18

larrykessl

Rookie

Joined: Apr 2023

Posts: 40

Likes: 5

From: CA

Quote:

Originally Posted by 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?

did you ever figure this out? I am having a similar issue; no led light on ignition and no door ajar light. Dash dead. I used to be ankecto wake it by touching 12 volts to the Lin line, but not any longer. I fear it’s my impossible to access ID code box

Mar 8, 2026 | 05:28 PM

#19

mmcd

Thread Starter

10th Gear

Joined: Mar 2022

Posts: 13

Likes: 0

From: wa

ignition key failure

No, managed to sell car at discount since nearest lexus dealer is now hours away. After the LIN method failed I found clicking lock/unlock on the fob worked for some months but then that failed. It's some intermittent on 1 of 3 ECU boxes buried behind the dash.

Quote:

Originally Posted by larrykessl

did you ever figure this out? I am having a similar issue; no led light on ignition and no door ajar light. Dash dead. I used to be able to wake it by touching 12 volts to the Lin line, but not any longer. I fear it’s my impossible to access ID code box

Mar 8, 2026 | 06:16 PM

#20

larrykessl

Rookie

Joined: Apr 2023

Posts: 40

Likes: 5

From: CA

Quote:

Originally Posted by mmcd

Thanks for the reply. It’s ridiculously complicated on these cars. I’ve spent major $$ and hours and got nowhere. It goes on the sales block later this summer after I reassemble what I took apart.
thanks again