2001 sr5 3.4 at 2x4

At startup I hear a repetitive sound like a hand pump being operated at about 1.5 cycles per second. That continues for about 30 seconds then the ABS and the BRAKE lights come on, accompanied by a very irritating high pitched scream. Sometimes I feel a bump in the brake pedal (if I am using the brakes) Then, the lights go off and the screaming stops, directly after a "pop" sound like a relay under the right side of the dash.

Duahhhh

Any ideas?

I feel you might have the beginnings of problems with your hydraulic brake booster/accumulator system. The 2001 and 2002 trucks have a very different setup than the earlier trucks, and seem to be prone to failing in various ways.

At a high level, the system uses an electric motor and pump to build pressure that it stores in the accumulator for the power brakes and traction control system. This is likely the sound you here when you start the truck. The lights and buzzer you here are warnings that the system detects a problem with it's ability to build proper pressure. The motor, pump, accumulator, or switches/electronics can fail over time. You can buy some parts individually to save some money if you can narrow down the issue to one specific part, but it's tricky. The system is under VERY high pressure, so be safe if you decide to dig into it.

I had to replace my master cylinder/booster/accumulator assembly last year to the tune of $2k for just the part. Yes you read that right. You can find them used for ~$500 but that's a bit of a gamble.

Do some searches here for "brake booster" or "accumulator". FWIW, the Land Cruisers of the same vintage also have this problem and there is a lot of discussion about the problems on the ih8mud landcruiser forum as well.

Good luck!

yep, know problem for the 2001 and 2002. Yes the brake master cylinder is $$$$. Look on the forums as this issue has been discussed often. there is some company in Cali that rebuilds them.