Nick69

Hey guys I'm in need of some help . I have a 2001 gmc 5.3 recently the check eng light came on so I ran the scanner and it says po327 low volt input . So I tested my wire going from the truck to the knock sensors and it read 4 volts when grounded to the battery but if I grounded it to the alternator bracket it read five so I made a ground wire from the bracket to the battery and retested and it read the proper 5 volts . Cleared the code and drove it and the code came back on so I decided to replace the knock sensors and the wire. Cleared the code and drove it Again and the code still came on it reads low input voltage bank 1/1 . Iv check all grounds on the truck any ideas what might cause this problem I'm out of ideas

tech2

these are piezo sensors that generate an a/c hertz signal and send it back to the pcm. It shouldn't be fed voltage.


If you feel the new part is good and don't need to test the new part, go right to this: disconnect the pcm connector and ohm check the connector wire back from the pcm to the knock sensor connector. Also check for short to grd and short to voltage.


if you want to test your new parts:
- ohms check of the sensor is ok 97-107kiloOhms
-tap on the engine block and see if you dvom picks up an a/c hertz signal when connected to the sensor connector.

Nick69

Yeah the wire coming out of the harness has five volts when the truck is running On bolth wire the light blue an dark blue . Before I hooked up that ground to the alternator it was only reading four . I'll try to test the wire from the PCM and see what it reads . Thank you for the response and help much apprieated as Iv tryed pretty much everything to fix this

Nick69

And that's what I didn't understand If they generate their own power then why is it being fed voltage everything Iv checked on the internet says that they should be fed five volts ? I don't understand this.