Kevin in Atlanta

I completed the flush a couple of weeks ago. No issues with completing the flush. Came back to do the slave and find there is no power to the pump.

Traced the issue back to the relay in the spare tire. Power at the fuse (all the time) 12 volts to the relay (30). I really should have jumpered the 30/87 but it was getting dark.

I get 8.75 volts across 85/86 with ignition on(should be battery voltage). 12.4 volts from the hot side of the relay (85 or 86 - don't remember which) to a good ground.

This leads me to believe I have a ground issue. According to the WSMs the ground is found at GP IV. GP IV is shared with the pump, the pressure warning switch and the relay.

Am I going in the right direction electron warriors?

Kevin in Atlanta

Wanted to capture here the ongoing conversation between Alan and I:

Quote from Alan:
In general you have the right idea. Battery power comes in to the fuse from C83 and feeds the motor via the relay contacts 2 & 8 and returns via the motor direct ground - this is to pump up the PSD pressure. The coil gets power on Pin 4 from the ABS relay. The other side of the coil Pin 6 is controlled by the PSD controller which grounds it to run the motor but feeds this through the pressure switch - stops when it is fully pressurized, by turning off the relay coil. The upper switch is used to interlock the PSD with the ABS - when the PSD is charged - if the ABS activates then the PSD controller - will disable the PSD function to ensure all power goes to the ABS and that there are no odd interactions between ABS and PSD (ABS takes priority).

I'd check the pressure switch

Relay Pin 4 should be @ battery voltage. Relay Pin 6 should have continuity to ground when the car is unpowered (and should stay grounded with ignition on until the pressurization is complete).

Quote from Kevin in Atlanta
As you can imagine this is all pretty challenging to me. But, this is what I am hearing. As soon as the ignition is turned on the signal to the relay is 'on' and remains on until the pressure switch says we have full pressure - at that point the signal to the relay quits thus the motor stops pumping until the pressure switch says the pressure needs to go up. My testing showed battery voltage at pin 4 when I grounded it to the body and 8.75 volts when I grounded it to pin 6 with the ignition on. So, we are thinking that the pressure switch is the culprit because insufficient voltage is being supplied- I think I am getting this. You wrote: Relay Pin 6 should have continuity to ground when the car is unpowered (and should stay grounded with ignition on until the pressurization is complete). Are you saying I should be able to use my multimeter set on resistance between pin 6 and a ground near the relay and it should be infinite? Thanks for your patience. Kevin

Quote from Alan:
If the PSD isn't pressurized - then with car off you should be able to measure ~0 ohms to ground on pin6 (use resistance mode) if this is much higher than a few ohms then seems like a pressure switch problem or a wiring issue to ground - check clean ground in spare tire well and check/clean the switch connector anyway. Then re- measure.

Ground reference for the DMM is always vehicle ground - or you will get very confused very quickly...