Einzelherz

I just recapped my ECU per the instructions in the pinned thread. Checked and double checked after I finished. I pulled one pad and a bit of trace, but I soldered a wire in its place and verified connectivity with my multimeter.

I reinstalled the ECU, plugged the battery back in and start it up. It's smooth and fine for about 5 seconds and then CHECK VSC pops up and the engine starts to sound like its timing has gone to ****. Pulled the code and got P1127. The gas pedal no longer works (which makes sense given the failure).

I assume I botched something in the ECU now. Unless there's a possibility that a fuse has gone bad or something. I tried checking the ETCS fuse in the engine bay but couldn't get its over off. I'll try again though.

If anyone has any other ideas or has encountered this, please lemme know.

YODAONE

Would be worth engaging an electronics technician to check circuit traces for continuity around the work areas.

Were you wearing a grounded wrist strap?

Wearing anything polyester (generates static cling charge)?

A Lexus wiring diagram should help determine which ECU pins trace to related circuit components.

Multilayer circuit boards add complexity when a pad lifts...

Yamae

Your words, "It's smooth and fine for about 5 seconds and then CHECK VSC pops up and the engine starts to sound like its timing has gone to ****. Pulled the code and got P1127. The gas pedal no longer works" remind me of the power supply circuit failed quickly after started. Did you mount capacitors correctly? Are there any reversed ones? I also worry about harnesses are partially damaged.

Einzelherz

I checked continuity on every pin that I soldered and they passed. Even the pad that I accidentally lifted checked out, at least on the surface that had its primary trace. Putting it against a backlight I can't see any other traces in the middle layer and there's nothing on the component side.

I would love to find a wiring diagram for the ECM but I haven't come across one. Do you know where I could find one?

All of the capacitors were polarized properly. The one whose pad was lifted is the 47uF Bipolar.

What I mean about "it's smooth and then CHECK VSC lights up" - It's almost as if the electronic throttle is locked out for a few seconds on startup. Then it seems like it engages but errors out and sounds bad. The gas pedal doesn't work even during that first 5 seconds.

Yamae

Can you identify the ECU's connector A? And can you identify pin#7 and #8?
Check the resistance between pin#7 and #8 of connector A (A コネクター, located at the left edge) both at the harness side and ECU's pin side. I'll give you an additional idea after you report back.

Einzelherz

On the bare ECU #7 and #8 read as 0 ohms.

For the harness - should the ecu be attached? should the car battery be installed? should the ignition be in any specific position?

Yamae

Completely 0.0 ohm?
There should be some resistance. Could you measure it again a bit more precisely reading at least 2 digits like 0.8 ohm?
The method is to remove the connector and measure the resistance both at the male and female side when the power is not applied.

Einzelherz

The harness says 1.63 ohm

The ecu is acting like the two aren't connected at all. It's not 0.00 like when you check the leads to each other. It just says nothing.

Yamae

Thanks for measuring again. The value 1.63 ohms means that the throttle motor is connected and the winding seems fine.
But the ECU side "OL" is strange. There should be at least some resistance since there is a winding sensing circuit connected. I worry that the line is open and not connected to the sensing circuit and the drive circuit. When you did the capacitors replacement job, you must have damaged something related to the throttle motor driving circuit. I'll check lines on the board connected pin#7 and #8 carefully.

Einzelherz

Pin 7 and 8 traces aren't visible on the back side. I'll try to find where they go tomorrow morning with the connectivity check.

Thank you for everything Yamae.

Einzelherz

Would the electrical wiring diagram manual help me with this? If so, would it have to be for the 98 or would any of the mk4, 98-00 books work?

YODAONE

The wiring diagram will take you from the inoperative component to the relative connector pin(s) on the ECU.

From there you follow the circuit board traces.

Not sure how th hat helps on a multilayer PCB.

Obtain a factory wiring diagram for your year LS400.

Lexus published LS400 wiring diagram manuals.

Are you adverse to asking a tech to check your work?

YODAONE

Wiring Diagrams posted.

Einzelherz

Thank you very much! I couldn't even find one of these to buy while googling last night. The connectors are labeled differently from Yamae's post, which is odd, but I see they are still the same pins.

Is there a circuit diagram in the book for the ECM?

I don't have any issue with someone checking my work, but I don't know who that is. Would I take it to Lexus?

On the plus side, the diagrams you uploaded, YODAONE have let me check that there's some resistance across the other two pins that control the throttle clutch.

Einzelherz

And to Yamae's post. I just realized that 0L means Over Limit. After cleaning up some of the flux and mess I'm now getting 190-200 M ohms sometimes, 170 M ohms other times and 140 M ohms other times. I suspect that's not good.