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Hey guys, new here and have a question/need some input. Truck is a 2006 Silverado 2500HD, LBZ Duramax/Allison 6 speed. Just rolled 201k miles today. Cold air intake, 100hp PPEI Kory Willis tune, EGR delete.

I've been having this problem off and on for about 2-3 weeks. ONLY in the morning when i go to start up, truck starts right up fine no issue, and runs perfect. However, here are my issues..

-The lights on the dash are dimmer than normal
-My RPM gauge goes completely crazy when I put on cruise control (cruise light doesn't come on but cruise does work)
-A/C doesn't work
-Blinkers don't work

Here's the weird thing.. After about driving 5 miles, it throws a MIL, and everything works perfect. Blinkers are back, cruise/rpm normal, AC back, light are bright as they should be. The codes im getting in the MIL are P0646, P0381, and P0650. All are related to low voltage. So I pull over and use my scan tool to clear the codes, and then no more check engine light the rest of the day, everything is normal. However, today i had to clear the codes 2-3 times because the problems came back shortly after. Here i am now, no MIL and everything is fine. BUT, it will happen again in the morning. This started happening about 2 weeks ago. It didn't come back all last week, but all of a sudden a few days ago , here we are again..

I had the batteries and alternator tested. Both tested as good. No blown fuses, nothing abnormal I can see.

I also should note.. I had gotten an Edge CTS2 Insight, and the problems started the next morning after installing. I ended ripping that thing back off, unhooked the batteries to reset ECM, and all was good. But a week later, we're back at it again.

Sorry for all the reading, im just giving as much info as I can. I'm stumped! Anyone can help with this?
 

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It sounds like a battery issue, I know you had them tested though. That said, we’re they both fine or was one a little weaker? Usually wonky electrical issues are tied to the batteries. I just went out and tightened all my battery connections and alternator connections because of some wierd stuff my truck was doing and it cleared things up. Did you get the batteries tested while they were having issues or after? Next time it has a problem, just pull the batteries and take them in to test maybe? I’ve never tested mine so not sure what the procedure is that they use :/
 

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May be your fuse box. Mice like to get in there and per all over everything, then it runs down and corrodes the fins from all the wiring harness connectors that plug into the bottom. Pretty much everything electrical in the truck runs through that box at one point so if there are a lot of different things acting weird, it would be a good place to start.

Pull the connectors and see if they are dirty or corroded.
 

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It does really sound like battery issues. Check all connections and make sure they tested the batteries separately.
 

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I would be surprised if this was a battery problem because once the truck is running the alternator voltage will exceed the battery voltage. I'd check your ECM voltage; low ECM voltage could indicate a bad ECM ground. You may be able to do this via your scanner, but bear in mind that the OBD port has its own electrical connection so it may not be obvious if the voltage displayed by your scanner is battery voltage or ECM voltage.

If that checks out, I'd check the relays for the circuits you mentioned. Or maybe check those first since that may be easier.
 

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P0646 - pull your a/c relay and see if problem continues or stops


DTC P0650

Diagnostic Instructions



DTC Descriptor

DTC P0650


  • Malfunction Indicator Lamp (MIL) Control Circuit

Circuit/System Description

The malfunction indicator lamp (MIL) is located on the instrument panel cluster (IPC). The MIL informs the driver that an emission system fault has occurred and that the engine control system requires service. The engine control module (ECM) monitors the MIL control circuit for conditions that are incorrect for the commanded states of the MIL.

Conditions for Running the DTC


  • The ignition is ON.
  • The DTC runs continuously when the above conditions are met.
Conditions for Setting the DTC

The ECM detects that the commanded state of the MIL driver and the actual state of the MIL control circuit do not match for greater than 2 seconds.

Action Taken When the DTC Sets

DTC P0650 is a Type A DTC.

Conditions for Clearing the DTC

DTC P0650 is a Type A DTC.

Diagnostic Aids

An intermittent or poor connection at the MIL control circuit in the inline harness connector may cause this DTC to set. Inspect the connector terminals for any condition that may result in excessive resistance.

Circuit/System Verification



  1. Ignition ON, command the MIL ON and OFF with a scan tool. The MIL should turn ON and OFF when changing between commanded states.
  2. Operate the vehicle within the Conditions for Running the DTC to verify that the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing



  1. Ignition OFF, disconnect the harness connector at the IPC.
  2. Ignition ON, verify that a test lamp illuminates between the ignition circuit and ground.
    • If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, replace the IPC.
  1. Connect a test lamp between the control circuit and the ignition circuit.
  2. Command the MIL ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    • If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM.
    • If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
  1. If all circuits test normal, replace the IPC.

DTC P0381

Diagnostic Instructions



DTC Descriptor

DTC P0381


  • Wait To Start Lamp Control Circuit

Circuit/System Description

Ignition voltage is supplied directly to the wait to start indicator. The engine control module (ECM) controls the lamp by grounding the control circuit via an internal switch called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line which is monitored by the ECM. When the ECM is commanding a component ON, the voltage of the control circuit should be low, near zero volts. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be high, near battery voltage. If the fault detection circuit senses a voltage other than what is expected, the fault line status will change causing the DTC to set.

Conditions for Running the DTC

The ignition voltage is greater than 6 volts but less than 18 volts.

Conditions for Setting the DTC


  • The ECM detects that the commanded state of the driver and the actual state of the control circuit do not match.
  • The condition must be present for a minimum of 5 seconds.
Action Taken When the DTC Sets



  • The ECM stores the DTC information in memory.
  • The ECM records the operating conditions at the time the DTC sets. The ECM displays the failure information in the Failure Records on the scan tool.
Conditions for Clearing the DTC



  • The history DTC clears after 40 malfunction-free warm-up cycles.
  • The DTC becomes history when the conditions for setting the DTC are no longer present.
  • The ECM receives the clear code command from the scan tool.
Diagnostic Aids

Using the Failure Records data may help locate an intermittent condition. If you cannot duplicate the DTC, the information in the Failure Records can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can help determine how many ignition cycles that the diagnostic test reported a pass and/or a fail.

The wait to start indicator illuminates only with the ignition ON and the engine OFF. The wait to start indicator will not illuminate during post-start glow plug operation. The wait to start indicator will not stay ON for long at higher engine temperatures.

Circuit/System Testing



  1. Ignition OFF, disconnect the harness connector X2 at the ECM.
  2. Ignition ON, verify that the wait to start indicator is OFF.
¤ If not the specified value, test the wait to start indicator control signal circuit terminal 16 for a short to ground. If the circuit tests normal, replace the instrument panel cluster (IPC).
  1. Install a 3-amp fused jumper between the wait to start control signal circuit terminal 16 and ground. Verify that the wait to start indicator is ON.
¤ If not the specified value, test the wait to start indicator control signal circuit terminal 16 for a short to voltage or an open/high resistance. If the circuit tests normal, replace the IPC.
  1. If all circuits test normal, replace the ECM.
 

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Hello first time post not sure if I'm doing this right. I have an 05 gmc sierra 2500HD sle crew cab 6.6 lly. I'm running a fass lift pump, I have a edge monitor, aftermarket radio just single din. Every so often I will be driving with a/c on and everything and my truck will put out 12.5-14v it goes up and down like crazy fast. All power will cut out, radio gauges except mph and rpms. It will continue to run like that for a minute or so then everything kicks back on. Now I'm noticing my headlights and all interior lights surging at night. I'm pretty sure the batteries aren't more than 2 years old and brand new alternator 6 months ago. Only owned the truck for about 9 months.
 

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Hello first time post not sure if I'm doing this right. I have an 05 gmc sierra 2500HD sle crew cab 6.6 lly. I'm running a fass lift pump, I have a edge monitor, aftermarket radio just single din. Every so often I will be driving with a/c on and everything and my truck will put out 12.5-14v it goes up and down like crazy fast. All power will cut out, radio gauges except mph and rpms. It will continue to run like that for a minute or so then everything kicks back on. Now I'm noticing my headlights and all interior lights surging at night. I'm pretty sure the batteries aren't more than 2 years old and brand new alternator 6 months ago. Only owned the truck for about 9 months.
was wondering if you figured anything out my 2004 lb7 surges and all interior and exterior lights flicker
 

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We own a 2016 GMC Denali Duramax. The other day my Boyfriend went to unlock the truck from the remote an it was like it was possessed. The door locks went up and down, Head lights flicked on and off, Horn blew the only way to stop it was to disconnect the battery. We took it to the dealers and they could not figure it out and gave us back the truck. We drove 1 block and the warning lights came on. We just bought two new batteries for the truck.... any suggestions?
 

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Hello first time post not sure if I'm doing this right. I have an 05 gmc sierra 2500HD sle crew cab 6.6 lly. I'm running a fass lift pump, I have a edge monitor, aftermarket radio just single din. Every so often I will be driving with a/c on and everything and my truck will put out 12.5-14v it goes up and down like crazy fast. All power will cut out, radio gauges except mph and rpms. It will continue to run like that for a minute or so then everything kicks back on. Now I'm noticing my headlights and all interior lights surging at night. I'm pretty sure the batteries aren't more than 2 years old and brand new alternator 6 months ago. Only owned the truck for about 9 months.
1> remove the Edge monitor from the DLC and see if problem goes away or changes
2> Remove and clean all of your battery cables, both ends, and also the alternator. Make them shiney clean with a wire brush or sand paper. Use a little dielectric grease on the connection when you reassemble. see if problem goes away or changes.
 

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We own a 2016 GMC Denali Duramax. The other day my Boyfriend went to unlock the truck from the remote an it was like it was possessed. The door locks went up and down, Head lights flicked on and off, Horn blew the only way to stop it was to disconnect the battery. We took it to the dealers and they could not figure it out and gave us back the truck. We drove 1 block and the warning lights came on. We just bought two new batteries for the truck.... any suggestions?
What warning lights? Go to an auto parts store like O'Reilly and ask them to scan your truck for codes. Record the codes in the same order they are displayed on the code reader.

Remove and clean all of your battery cables, both ends, and also the alternator cable. Make them shiney clean with a wire brush or sand paper. Use a little dielectric grease on the connection when you reassemble. see if problem goes away or changes.
 

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Thank you Ron, Im not sure and will ask what the warning light on the dash was. I believe the dealership ran it an cleared the codes ? We will try what you suggested. Thank You !!
 

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Could I also suggest removing and cleaning all of the grounds because they will cause a lot of problems without issues that can't be pinpointed. Besides grounds are a quick and easy step.
 

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Could I also suggest removing and cleaning all of the grounds because they will cause a lot of problems without issues that can't be pinpointed. Besides grounds are a quick and easy step.
Does anyone know if there's ever been a comprehensive list of grounds put together? I know where some of them are on my LML but I'm sure there's 1 or 2 lurking somewhere that I'm not aware of.
 

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Start here: https://www.gmupfitter.com/pages/body-builder-manuals
Then look for your year and model, and then look for the electrical manual. Not every year has an electrical manual that has all the grounds, so go a year earlier or later and you'll know more about Silverado grounds than almost all of mankind on earth
 
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