Compression Ignition Addict
Join Date: Aug 2008
Location: Madison, WI
Thanked 135 Times in 131 Posts
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Very unlikely O'Reilly's could even have scanned the truck. As said, get a code reader on it, but more specifically, one that's known to be capable of communicating with the OBS PSD.
ONLY California trucks can throw any codes related to the GPR, and as is the case with ALL codes, ALL vehicles, the code references the part REPORTING the error, which is NOT necessarily the part (if any) at fault. But stores like O'Reilly's and AutoZtoned like to scan your vehicle, _interpret_ the code(s) (rather than giving you the codes themselves for you to research yourself), and handily interpret them in ways that reference parts that, oh golly, they just happen to stock.
Classic definition of a racket. Always, ALWAYS, when using such "services", with ANY vehicle, just get the code(s) and do your OWN research. In this case, the GPR you bought was probably your typical FLAPS relay that doesn't have the duty rating to run our glow plugs, for the time period our PCMs are programmed to run them.
Why did you remove the HPOP? If the truck runs well once it's started, it's extremely low on the suspect list.
Put the truck back together and start TESTING. The above statement about throwing parts at the problem applies to ALL vehicles; it just goes doubly so with these ones.