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2018 L5P codes. P129F & P228C

Danny R
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Danny R Enthusiast

Danny R

Posted
Posted

My 2018 GMC 2500 Denali 2500 Duramax L5P Has 2 codes. P129F & P228C. It still runs but you have to feather the throttle to get it up to speed. It also goes into a reduced power mode. I have read that there may be some wiring issues to the lift pump. It seams that the lift pump is making a strange noise during the initial key on 30 second run time. I have also read up on the lift pump but it is some kind of 3 phase variable speed pump that I am not familiar with. Any info will be appreciated. My truck has 20K miles on it. and has not given me any issues up to now. No mods have been done to it.

newdude Senior Enthusiast

newdude

Posted
Posted (edited)

P228C is a regulator low pressure code but it sounds like the P129F is what is causing that.  

 

P129F Fuel Pump Driver Control Module Fuel Pump Speed Signal Incorrect.  Could be a bad in tank pump/sending unit assembly or bad fuel pump flow control module.  

 

If you've got warranty still, take it in and let the dealer deal with it.  

Edited by newdude
Danny R Enthusiast

Danny R

Posted
  • Author
Posted
5 hours ago, newdude said:

P228C is a regulator low pressure code but it sounds like the P129F is what is causing that.  

 

P129F Fuel Pump Driver Control Module Fuel Pump Speed Signal Incorrect.  Could be a bad in tank pump/sending unit assembly or bad fuel pump flow control module.  

 

If you've got warranty still, take it in and let the dealer deal with it.  

Thanks. No warranty but thats a story for another day. Im gonna need to find some troubleshooting procedures to determine if its module or lift pump but I think I have a source for that. I'll update next week when I get back on it.

newdude Senior Enthusiast

newdude

Posted
Posted (edited)
10 hours ago, Danny R said:

Thanks. No warranty but thats a story for another day. Im gonna need to find some troubleshooting procedures to determine if its module or lift pump but I think I have a source for that. I'll update next week when I get back on it.

 

 

Here is the diag from GM for P129F:

 

 
Quote

 

Circuit/System Verification
  1. Ignition On.
  2. Verify DTC P1029, P102A, P102B, P1255, P12A6, or U18A2 is not set.
    • If any of the DTCs are set

      Refer to Diagnostic Trouble Code (DTC) List - Vehicle.

    • If none of the DTCs are set
  3. Verify the scan tool parameter:
    • Fuel Pump Phase U-V-W Circuits Shorted Test Status = OK / Not Run
    • If not the specified state

      Refer to: Circuit/System Testing

    • If the specified state
  4. Engine running.
  5. Verify scan tool parameters Fuel Pump Speed Command and Fuel Pump Speed are within 250 RPM of each other while operating the vehicle through varying loads.
    • If not within 250 RPM

      Refer to Circuit/System Testing

    • If within 250 RPM
  6. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
  7. Verify DTC P129F did not set.
    • If the DTC is set

      Refer to Circuit/System Testing

    • If the DTC is not set
  8. All OK.
Circuit/System Testing

Note: It may be necessary to remove engine components for the visual inspections.

  1. Ignition/Vehicle & All vehicle systems » Off
  2. Disconnect the electrical connector: @ K111 Fuel Pump Driver Control Module & A6C Fuel Pump and Level Sensor Assembly - Primary
  3. Test for less than 2 Ω between the test points:
    • Control circuit terminal 8 @ Control module harness & Terminal 1 @ Component harness
    • Control circuit terminal 9 @ Control module harness & Terminal 2 @ Component harness
    • Control circuit terminal 24 @ Control module harness & Terminal 3 @ Component harness
    • If 2 Ω or greater

      Repair the open/high resistance in the circuit.

    • If less than 2 Ω
  4. Test for infinite resistance between the test points:
    • Control circuit terminal 8 @ Control module harness & Control circuit terminal 9 @ Control module harness
    • Control circuit terminal 8 @ Control module harness & Control circuit terminal 24 @ Control module harness
    • Control circuit terminal 9 @ Control module harness & Control circuit terminal 24 @ Control module harness
    • If less than infinite resistance

      Repair the short between the circuits.

    • If infinite resistance
  5. Verify a condition does not exist with the component: A6C Fuel Pump and Level Sensor Assembly - Primary
    • Restrictions
    • Debris
    • Contamination
    • If a condition exists

      Repair or replace as necessary.

    • If no condition exists
  6. Replace the component: A6C Fuel Pump and Level Sensor Assembly - Primary
  7. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
  8. Verify the DTC does not set.
    • If the DTC sets

      Replace the component: K111 Fuel Pump Driver Control Module

    • If the DTC does not set
  9. All OK.

 

 

 

Edited by newdude
Danny R Enthusiast

Danny R

Posted
  • Author
Posted
On 11/28/2020 at 7:24 AM, newdude said:

 

 

Here is the diag from GM for P129F:

 

Wiring checks out good. Pulled pump today. Gonna try that first. Thanks for the info

 

 

 

Danny R Enthusiast

Danny R

Posted
  • Author
Posted

Installed the new lift pump and I still have the same issue. What fuel pressure should I be seeing at idle on the low pressure side and the high pressure side and also how high does the high pressure side run at speeds? I do have a fuel pump driver module on order. Should have tried that first cuz it's a third of the price of the fuel pump but I was just following diagnostic procedures.

Danny R Enthusiast

Danny R

Posted
  • Author
Posted (edited)

Replaced the Fuel pump driver control module and reprogrammed the ECM with all the current updates and now I'm back in business. Even seems to be a little stronger and a little less noisy! Thanks for all the advice. Lesson learned. I'm into it for about $500 cuz i replaced the in tank fuel pump first but I'm not complaining. Would have been way more at the dealership!

Edited by Danny R
  • 7 months later...
  • 4 weeks later...
Mtzcesar65 New Member

Mtzcesar65

Posted
Posted (edited)

Hi 

I got a Chevy 2500 HD with the duramax 6.6L engine and this is what happened to mine, i stop at Orileys for about 5 min and truck wont start, it will crank but not start, didnt had any code befor this, tried to get it running twices and CEL came on, i got a cheap scanner from Orileys (Innova) so i scanned and pops P129F- Fuel Pump Driver Control Module, Fuel Pump Speed Signal Incorrect, and shows 2 more codes for the glow plugs, erased checked for any loose harness, and got it running, the second time was that same day in the afternoon, crank the engine and will start but rough, like if the starter was kicked in all the time. turn it off twice and fire up again normal, it didnt do it for like a month, and again today couldnt start the truck, same codes, couldnt erase it this time so tried to reset ECM by disconect the batteries and it works, but i turn it off and again couldnt start the truck again, will crank but wont start and same codes 2 for glow plugs, and the one P129F for the fuel pump. DOES THAT SOUNDS LIKE A BAD CONTROL MODULE? OR SHOULD I GO STRAIGHT TO THE FUEL PUMP IN THE TANK?  CAN SOMEBODY HELP ME WITH THIS?

 

THANK YOU 

Edited by Mtzcesar65
Tom Dixon New Member

Tom Dixon

Posted
Posted
On 7/31/2021 at 2:41 AM, Mtzcesar65 said:

Hi 

I got a Chevy 2500 HD with the duramax 6.6L engine and this is what happened to mine, i stop at Orileys for about 5 min and truck wont start, it will crank but not start, didnt had any code befor this, tried to get it running twices and CEL came on, i got a cheap scanner from Orileys (Innova) so i scanned and pops P129F- Fuel Pump Driver Control Module, Fuel Pump Speed Signal Incorrect, and shows 2 more codes for the glow plugs, erased checked for any loose harness, and got it running, the second time was that same day in the afternoon, crank the engine and will start but rough, like if the starter was kicked in all the time. turn it off twice and fire up again normal, it didnt do it for like a month, and again today couldnt start the truck, same codes, couldnt erase it this time so tried to reset ECM by disconect the batteries and it works, but i turn it off and again couldnt start the truck again, will crank but wont start and same codes 2 for glow plugs, and the one P129F for the fuel pump. DOES THAT SOUNDS LIKE A BAD CONTROL MODULE? OR SHOULD I GO STRAIGHT TO THE FUEL PUMP IN THE TANK?  CAN SOMEBODY HELP ME WITH THIS?

 

THANK YOU 

I just had the same problem and thought it was the lift pump as well. Had to have it towed to dealership. Found it was the control module. What I found they get overheated and stop working.  Had the same issue with it wanting to start and run but after turning off, I had to turn the key on and off several times to get it to work but that finally stopped working. It was under $400 at dealer to repair but I have a warranty that covered it. From research on different forums the lift pump really doesn’t go bad, just the injection pump and this module. Hope this helps!

  • 7 months later...
Tunaonrye New Member

Tunaonrye

Posted
Posted
On 12/7/2020 at 2:41 PM, Danny R said:

Replaced the Fuel pump driver control module and reprogrammed the ECM with all the current updates and now I'm back in business. Even seems to be a little stronger and a little less noisy! Thanks for all the advice. Lesson learned. I'm into it for about $500 cuz i replaced the in tank fuel pump first but I'm not complaining. Would have been way more at the dealership!

Hey, so I think I just had the same failure. 18 Silverado L5P 38k.  At the pump, fill it and crank… no start.  Of course getting a module looks like it’s going to take some time.  But could you tell me where it’s located on the truck?  Thank you in advance.

  • 2 years later...
Bdock1981 New Member

Bdock1981

Posted
Posted

I have a 2018 GMC Sierra 3500. I keep getting the crank no start with code P129f. I have an Autel scanner and it says that it stores a permanent code of p129f. I let it set for 5 minutes or 3 days sometimes before it will start. Funny part is, after it restarts the engine light goes out. Took it to the dealership twice for this problem and they “say” that code shows no where in the history. What should I do????

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