I have an 04 Cummins I've had for 3 years. I've had nothing but problems with it. Found out the guy I bought it from was racing and pulling with it. It had a programmer on it but isn't on anymore. Long story short I've had a codes popping up out the ***. These are the codes I have, P2121, P2127, P2123, P0201, P2127, P0202, P0203, P0204, P2509, P2146. It's a lot. I'm not sure if this could be all a computer issue or a lot of wiring issues. I did lose my gas pedal once so I think the sensor may need replacing. The rest I'm not sure about. I don't know where to start. Any help would be appreciated

 

I would start by cleaning all battery grounds and terminal connections. After that take a look at the wiring harnesses going to injector bays- these will be on the drivers side of the valve cover. Also check your rail pressure sensor etc. Usually a string of codes are started by one triggering the rest.

 

Knockout P2509 first. Check all battery connections and ALL grounds. Make sure they are clean and tight. See what your alternator is putting out, get your batteries tested, check all the plugs on the bottom of your TIPM making sure there is no corrosion or broken pins and do the same for the ECU plugs.

 

I know it's an old thread but I have some codes I need help with and I can't figure out how to start a new thread
P0118 p0483 p0524 p0234 p2503 p2502 p2509 p0073

 

It's an 03 24 valve HO

 

As somebody already stated start with the P2509 resolution and see where it goes from there

The causes for this DTC may include:
Battery failure
Poor connection at the batteries
Alternator is either overcharging or undercharging
Large voltage drop through loose or corroded cables
Electrical clutch fan short to ground
Bad connection at ECM
Leaking diode
Battery + positive shorted to ground or other circuits
Open or return ground circuit

Read more at: https://www.obd-codes.com/p2509
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did you read the thread and try anything i mentioned?