I don't know what the high pressure relief valve is. Probably under the HPOP cover, and we'll be tearing into that next week.

We applied a few psi of air pressure to the screen end of the IPR, and air escaped through the larger holes in the shaft. Then we applied 12 volts to the valve and again applied air to the end, and air still escaped at the same rate. Messed around with it for a while and after actually banging it on the table the valve would audibly click and shut and not allow air through. This led us to believe the valve was bad, so we put in another valve. However, the truck's HPO leak symptoms persisted after buttoning everything back up again.

So how do you test the IPR with a diagnostic tool, and are you certain it functions on 12 volts?