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Discussion Starter · #1 ·
I need some help with these codes before I just take it to a shop to get it fixed.

I've been trying to figure out a common cause for these codes, and so far Ive come up with the relays. So I replaced both relays, and what do ya know, didn't fix my problem. Codes are back, the P0380 came back right away, while the P0540 came back a few days later.

Something to note however, when I was attempting to diagnose my problem.
I noticed, my glow plug voltage was at 11.7 or so with the relay turned off, turned the relay on, and my scanner said that the glow plugs timed out or something to that extent. Also the voltage stayed the same at 11.7 or so.

I figured with the voltage staying the same it would have been a relay problem, like I said I replaced it, and nothing happened..... what else could be causing the voltage to stay up so high? If Im not mistaken, when the relay is turned off shouldnt the voltage drop to almost 0?

What are common causes of these 2 codes, they seem to be synonymous...
 

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California or federal emissions? The 175 amp fuse is good?
 

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Discussion Starter · #3 ·
I just replaced it. So it's not the fuse, the fuse may be the cause of the P0540. So it's possible it blew again, but why?

I know it's not the cause is the P0380 though; at least thats my understand.
 

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I'm not sure if you've done this yet, but when I bought my 02 Duramax, it had the 380 code. I replaced the glow plug controller and went ahead and put new glow plugs in and it cleared it.
 

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This is the schematic for your setup. That fuse powers both components. Can you check and make sure it isn't blowing the fuse?
 

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Discussion Starter · #7 ·

This is the schematic for your setup. That fuse powers both components. Can you check and make sure it isn't blowing the fuse?
Holy hell, I have no clue what I'm looking at haha. But anyways, Ill take the fuse off tomorrow and see if its blown, I would assume yes, considering replacing it seems to keep the p0540 code away for a few days, so something must be blowing it. Still doesn't explain the P0380 however.
 

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If your 175 AMP Fuse is Blown again, it's likely you have one or more Glow Plugs or Assocated Glow Plug wiring with a Short. OHM Out Each Glow Plug,
and associated Glow Plug wiring with Battery Negatives Disconnected. When you rewire each Glow Plug, Make sure you have a Clean and Secure Connection.

You need to verify the voltages in both the CONTROL and POWER sections of BOTH sections of the circuits (Glow Plug Relay = P0380 & Intake Air Heater = P0540)

POWER CIRCUIT
The Battery Fuse (175 Amp) supplies the Voltage (& Current) for the Glow Plugs and Intake Air Heater through a couple of Fusable Links, Glow Plug Relay, associated Relay Base, and more Fuseable Links to the ECM (as INPUTS to the ECM = FEEDBACK or Signals to ECM)

CONTROL CIRCUITS
Glow Plug
The Control Circuits are the Coils of the Glow Plug Relay, Associated Relay Base, OUTPUT Control Signal from ECM to Energize Glow Plug Relay, and Ground G108 for Glow Plug Relay.

Intake Air Heater
The Control Circuits are the Coils of the Intake Air Heater Relay, Power from Fuse FUEL HT (15 AMP), a fuseable Link, two INPUTS to ECM (C1 & C2) and and the
Intake Air Heater Relay Control (which is a "LOW" Signal at ECM to Energize the Intake Air Heater Relay).

If you chase the Voltages through all four Circuits (POWER & CONTROL) for both Relays (Coils & Contacts) you should locate the problem.

Post what Voltages you find starting at the 175 AMP Fuse, and where it's missing. Start with POWER Circuit, then Control Circuit (of Glow Plug Relay, then Intake
Air Heater Relay).


Larry
 

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^What Idkraemer said.. I was looking and working at the same time and only had enough time to post that. And that is a simple schematic compared to some. lol
 

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Discussion Starter · #10 ·
I just checked the fuse again, seems to be good. Guess Ill be spending a while under the hood checking everything...
 
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