pishta

Just got this car but it has a history of the TRAC buzzing and the TRAC light coming on the tach. The buzzing will stop and all is well, it just does it randomly. Sounds like a pump is cavitating or sucking air or something....? I dont even know what the TRAC does in this car or how it works.

KahnBB6

iTrader: (5)

pishta, I can't offer much help to you with the actual issue, sorry, but I can tell you that "TRAC" was the optional (but extremely common) traction control system Toyota/Lexus designed for many of their cars made through the 1990's. Most SC300's with automatic transmissions have it and most SC400's have it.

It uses an additional butterfly valve inside the throttle body (that is normally in an "open" state) with a motor on one side to modulate it. It operates the same way on both the 2JZ-GE (SC300) and 1UZ-FE (SC400) in conjunction with its own pump module, additional ECU and the ABS sensors on the car. When low traction or wheel slip is detected its primary function is to close that additional butterfly valve and pull engine timing to temporarily remove power to the rear wheels.

It's a somewhat aggressive and clunky system but it was designed when traction control for commercially available cars was still a new thing and at the time (early 90's) it was impressive.

Your TRAC system does appear to be malfunctioning. I am not sure if this means it simply won't activate in a low traction situation or not right now but the issue may be in the TRAC pump itself... but I am not familiar with these other than the basic principal and operation, sorry. It should be diagnosed through the SC400 factory service manual to see what part of the system is failing on you. I know some folks here are much more familiar with the system's quirks than I am. Sorry I cannot be of better help to you with discovering the malfunction culprit :/

pishta

well, I bled it according to the posts about running the pump and purging the air bubbles out of the pump and accumulator. You make an SST with some jumper wire: there are 3 pins in the pump harness in a row 1,2,3 from top to bottom. Top 1 is negative and 3 bottom is positive. jump the pins with a wire straight to the battery. First crack the pump side bleed port with a 10mm and put a clear tube onto the nipple and then run the other side straight into the brake fluid reservoir. Connect the jumper sire and cycle the pump for 10 seconds, cut it 2 seconds then run it 20, cut it and then run it for 60 seconds. If there are any bubbles in there they should shoot through the clear tube and dump into the reservoir. After 60, tighten bleeder and remove hose. Move over to the other side and do it again with an 8mm but catch the fluid in a cup. NEVER cycle the pump long enough to suck the reservoir dry! Youll end up doing much more work to get it purged again. Just keep catching and filling until no more bubbles are present. I bet 60 seconds is about right. WEll see if this helps. I had no bubbles whatsoever in my system but it tripped the TRAC light on the dash last night after about 7 miles. You can hear the pump run for about 15 seconds, then itll stop and about 5 seconds later itll light the TRAC light.