“Hi there, I had exactly the same problem with my 1990 XJ40. Turned out it was an in line fuse in the footwell. Took about 10 minutes to locate and replace for a couple of dollars.”
Thanks for the help. Wish I had a 90 they did use an electric hydraulic pump… not so on 88-89 XJ40 they used an engine driven radial 3 piston mini pump bolted to front of engine… but rest of 88-89 system is fairly complicated…
Car off checked the 2 switches on the accumulator sphere assembly one was open the other closed at the GREEN Amphenol connector.All seems normal as per posts on Jaglovers.
Plugged green connector back together…
Disconnected YELLOW connector to Girling valve body
The Charge Solenoid measured 30 ohms. All looks normal.
Started Car, foot on brake, no power assist no normal pedal drop, still low pressure warning on dash VCM and of course no power assist.
Stopped engine left KEY on
Mechanics Stethoscope on CHARGE solenoid (top of assembly towards front of car) , alternately disconnected its POWER–YELLOW connector, on off, on off,— (it was getting 12 volts) --we years back installed charge volts monitor LED & resistor on this connector it was nicely glowing red—
Stethoscope on CHARGE solenoid I could hear a small but distinct CLICK inside as I opened and closed the power to it. Again it seems OK.
Reading mores posts. It appears sudden loss of power assist could be.
Charge valve not opening or its clogged
Hydraulic BOOST at master cylinder its SPOOL VALVE my be stuck allowing high pressure fluid to pass right through the booster and not getting any booster boost (BB to Jagmen).
Removing Charge solenoid may be next step look for micro dirt.
I have a brand new hydraulic booster… maybe Ill swap lines temporary leave the old booster mechanically connected (seems complicated to release its front clevis connection) but swap the 2 hydraulic lines to new booster and see if LOW PRESSURE on dashboard VCM goes away. That would tell me if it’s the spool valve…
Not sure why I could not just block the High Pressure lied to the booster with say a cap??? and see if it then builds pressure and turns off the dashboard LOW PRESSURE warning.
I have a Waken pressure gauge maybe check for high pressure at inlet but not sure If I have the proper connector…
Anyone tried just blocking the boosters HPressure line and see of the LOW PRESSURE warning goes away??