Abs issue some work done but stuck?

[grundsethp]

My suspicion has been confirmed that the high pressure switch is not switching.

In the 2004 diagnostic manual ( look in the stickies under lc100 faq)
There is a diagnostic check for the sensor:

Depress the brake pedal more than 40 times or until stroke becomes longer.

In the manual it says to check the connector. Remember to check the pins on the master cylinder side of the connector, not harness. When disconnected, the harness side goes to the abs controller so you will measure the pull down or pull up resistor value in the controller, not the sensor.

When Pressure is Low
High Pressure switch output (see page DI-582 in manual for connector)should be 1.0 kohm (mine works).
Low Pressure switch is 5.7 kohm.(works also)

When pressure is high
High Pressure switch output (see page DI-582 in manual for connector)should be 0 ohm (still reads 1kohm)
Low Pressure switch is 1.0. kohm.(works also)

So the sensor is either bad or I have air in the system and when its cold, the pump cannot reach the pressure.

I am going to try to actuate the ABS multiple times and then flush the brake fluid again. Already did this twice. Maybe I need to take it to Toyota for an official brake flush.

 

[grundsethp]

The pressure switch does work after warming up and the resistance is 1.5 ohms when pressure is high.

 

[grundsethp]

I have ordered a techstream and going to try to bleed the abs vsc system to see if that fixes the cold problem.

 

[grundsethp]

Bleed my brake using techstream but no change. The high pressure sensor does not work until it warms up.

I did find this:
http://www.toyota-4runner.org/4th-g...8-4runner-abs-pump-problem-any-solutions.html

Looks like a 4runner had the same issue and his solution was to pump the brakes at the end of the day to lower the pressure. I will try that tonight and see if works tomorrow morning.

 

[grundsethp]

Does anyone have an old brake master w/o a booster pump they are looking to get rid of?

 

[grundsethp]

The pump shutoff twice momentarily this morning. I pumped the brakes last night which ledt the pressure low overnight. I will try a few more days and see if this solves the issue.

 

[grundsethp]

So for the last few days I have depressurized the brake system to see if the high pressure switch starts working at low temps. The high pressure switch worked correctly this afternoon but the temperature has been a bit warmer(46F). Drove around for 10 minutes with no faults.

 

[nckwltn]

So for the last few days I have depressurized the brake system to see if the high pressure switch starts working at low temps. The high pressure switch worked correctly this afternoon but the temperature has been a bit warmer(46F). Drove around for 10 minutes with no faults.

What did you end up doing to resolve the issue? I'm having a similar issue where when my HBB is pressurized over-night, the high switch is stuck "on" (which means that the pressure isn't high enough) and that causes the pump to keep pumping and creates the screeching