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Acceptable Volt Drop Number For PCM Grounds

  • rome83
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06 Aug 2019 07:31 #32534 by rome83
Hey guys, what do we consider acceptable volt drop for PCM earth points? I have an Australian car(Holden Commodore) with the oil warning light on the dash and DTC P0522 Engine Oil Pressure Sensor Circuit Low Voltage. 3 wire oil pressure sensor - power - ground - signal to pcm. Tested power and grounds under load and all good. Signal wire is within spec when plugged in running and unplugged so I have confirmed all circuit integrity is in tact. I suspect an internal fault in the PCM considering there are other issues going on too(Maf circuit codes even though the Maf has been disable with HP tuners & intermittent no start due to BCM not receiving correct code from PCM for start up) - just wanted to make sure that they were no grounding issues with the PCM itself - 4 ground wires - 3 of them have around 78mv drop with key on and 1 has 3mv drop. I can't find any spec to confirm what those numbers should be and I don't really know from experience what an acceptable number is. Would love to hear your thoughts.

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  • Tyler
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08 Aug 2019 09:42 #32601 by Tyler
I like those voltage drop numbers. :) The only suggestion I would make is to redo those checks with the engine running, if possible.

I don't have the wiring diagram to check, but I'm willing to bet at least one or two of those grounds end up on the engine. Having the engine running or not can change how a ground gets loaded, and therefore your drop numbers. It probably won't matter? :silly: But just to be safe.

So do you believe it's a genuine PCM hardware problem, or a PCM software problem? No insult to HP Tuners meant, but they can do strange things. :silly: I wonder if you short the EOP 5V to the signal, would it set a high voltage code?

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