95 LS400 - Trac stopped working

[Nunev]

Hello, I am driving a 95 UFC20 LS400 for almost two years now and everything was great so far. However, last month the traction control (Trac) stopped working. When I start up the car without depressing any pedals everything is fine and there are no warning lights. When I depress the brake pedal, the brake warning light with the exclamation mark lids up. A few seconds later the Trac warning light starts blinking. My LS uses the pre-OBD2 standard, which works via blinking codes so I've managed to get a reading on the error codes. I get TRAC error codes 52 and 53 and also engine error code 21. Now I have the full LS400 service manual, which tells me 52 on the Trac is brake fluid level low error and 53 is ECM communication error or something. I tried draining some of the brake fluid from the reservoir via a syringe so that it goes below the Min level. Afterwards when I turn the key on the warning light with the exclamation is always on without even pressing the brake. When I refilled the fluid to reach the MAX level I was now back to stage 1 - the light only turns on when I depress the brake pedal and afterwards the Trac starts blinking. Now this tells me that the brake fluid sensor should be working fine. I failed to mention that my ABS is working perfectly, it is only the Trac that does not want to work. Also, my brake switch is working normally as my brake lights light up when I depress the brake pedal.

Could this be caused by the notorious bad caps in the ECUs? Has anyone encountered this problem and what would you advise me to do?

[Malc]

Marin hi and welcome                       I have a UK  Mk3  October 1995 Ls400 and never had Traction Control on my car !

Not sure if any member here can help, it was available on later cars for sure in the UK, the Mk4 so hopefully someone can give you some useful thoughts

Best wishes with it all

Malcolm

[steve2006]

Hello Marin and welcome to the LOC.

Have you tried disconnecting the Battery for a short while to reset everything and are all your brake pads good?

I have also read you can reset the trac by pressing the brake pedal 8 times within 3 seconds!

If I find anything else I’ll post it up.

[Tinonline]

Deferring to my experienced colleagues...try what they suggest.

Might be a motion sensor moment and plugging in to get a fault code might be a start.

I’ve had that light on when I’ve jacked up the car and have been meddling all over the place. Also had the light on at random but on restarting it has gone out...haven’t had this now ever since...but it was a recurring event for a few times. It just stopped...

Worth covering a few basics: brakes are clean and have meat, fluids are ok...if you can check break pad sensors...I know a different light should show...

Annoying but nothing to worry about. But need to resolve...for peace of mind and safe motoring. 

 

 

[Nunev]

Thank you for the suggestions. I've changed the front and rear discs and pads. The parking brake pads are almost at the end of their life but I have not changed them yet. The front wear sensor was intact when I changed the front brake and pads. The rear wear sensor is shortened out by any of the previous owners. So that should not be the case. I tried both disconnecting the Battery for more than 10 seconds and depressing the brake pedal 8 times within 3 seconds. The error still persists. As I've said before. When I start the car, nothing lights up on the dash. The moment I touch the brake pedal, the brake light with the exclamation mark (!) lights up. A few moments later the TRC starts flashing.

The error codes I pulled are the following:

TRAC

DTC 52 - Brake fluid reservoir level low

DTC 53 - ECM communication circuit malfunction

Engine

DTC 21 - Not sure whether this one is related to the TRC or whether it is for the o2 sensor

What baffles me is the DTC 53. If I had a faulty ABS & TRC ECU I think I should lose both ABS and TRC. However, my ABS is working fine.

[runsgrateasanut]

Silly thought - arn't we suppose to start the Car with our foot on the brake pedal?  Can't offer any thoughts as don't have trac

[steve2006]

Just reread your first post, had another think about this and would agree that the engine ECU is susceptible to capacitor leakage, this causes many problems.

https://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/656360-all-my-crazy-lexus-issues-solved-ecu-leaking-capacitor.html

Have you also checked the wiring and connections from the brake fluid level sensor  as the code suggests low fluid when it obviously isn’t?

I don’t have the wiring manual for your year but the picture is from my 2000 year book showing the brake fluid level switch and wiring which may be similar.

[steve2006]

Again for a 2000 year model but it clearly shows that the engine ECU has inputs to the TRAC ECU so if the caps have failed it could affect the TRAC system.