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jokerfabworx.com
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ChevyTech77, 9.7 volts between the driver's side positive terminal and the block during cranking, when it is 21°C outside.
Like I said earlier, it behaves like a poor ground. That said, it is likely more than just a partially corroded ground terminal, since both Ken's LML and mine show the same voltage at the plug. There must be a hard fault somewhere.

My Tech II says that 3.4 volts are being sent to the GPs when commanded "on".

The dealership's diesel techs had the truck for ten days. They tested the GPCM and ECM, both of which were deemed "good". The techs installed all firmware patches on the GPCM and ECM, with no changes. They tried to blame the Diesel Rx glow plugs, so I let them install an ACDelco plug, and they got the same .95 volts at the plug.

All scan tools will determine that the GP system is functioning correctly, even though the proper voltage is either not being sent to, or not reaching the GPs. Probing a GP lead between the GPCM and a GP is the next step, to see if the GPCM is actually sending the voltage the Tech II is reporting.
 

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12.46 volts at rest.
So first off, 12.5 volts is 75% state of charge.

Secondly, if you’re dropping almost 3 volts, you’ve got issues. Keep doing the same test, section by section of all of the main grounds and power cables until you find the section causing the drop. Charge the batteries first.
 

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jokerfabworx.com
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So first off, 12.5 volts is 75% state of charge.

Secondly, if you’re dropping almost 3 volts, you’ve got issues. Keep doing the same test, section by section of all of the main grounds and power cables until you find the section causing the drop. Charge the batteries first.
How should we test the individual grounds and cables?
 

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How should we test the individual grounds and cables?
DVOM connected to each end of each cable you want to check, set DVOM for dc voltage, crank engine for a load. Nothing over 300 mv. A DVOM with min/max/average record, like a Fluke 87 works best to catch this.
 

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jokerfabworx.com
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DVOM connected to each end of each cable you want to check, set DVOM for dc voltage, crank engine for a load. Nothing over 300 mv. A DVOM with min/max/average record, like a Fluke 87 works best to catch this.
Perfect. I can get to this when I get back from work. Do you know the locations of all the engine ground locations by chance?
 

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Perfect. I can get to this when I get back from work. Do you know the locations of all the engine ground locations by chance?
Depends on model year (GMT900 vs K2). Easiest to just start with the cables at the battery and work your way in. IIRC, GMT900's grounded one batt to the block and one to the frame horn under the rad core support. All dmaxs usually have all of their important grounds (including the one for the gpcm) on both sides of the block, down near the upper oil pan rail.
 
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