2006 mustang GT throwing codes CEL C0500 P0103 C0503 CC0900 P0203, PCM is bad?

nahr123

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Hi guys, I would like to hear some opinions on this issue. I suspect a bad PCM.

I have been working on the car lately and for the past few months I have been dealing with numerous CEL codes. It all sorta happen one after the other, leaving me to believe its the PCM.
As you can see in the pic it's throwing following codes: C0500 P0103 C0503 CC0900 P0203. Some codes stay some go and come back again. Sometimes it changes from current fault to pending faults. Other then that the car seems to run fine. It seems to pull good too.
Been trying to sort these issues out with no luck. I changed MAf sensor + connector, replaced alternator, new bigger battery + new head unit (had to change it due to stock radio draining battery), cleaned all 8 fuel injectors, swapped injectors, swapped coils, swapped front wheel speed sensor, replaced abs module, checked conncetions to ABS & PCM no corrotions, Checked SJB no water leakage no corrotion.
With the OBD scanner I was reading between 13.0 and 13.8 volt. Had a corroded terminal wire coming from the alternator. Replaced it and now it reads 13.8 to 14.4 volts so I know the new alternator is good.

This indicates it certainly is the PCM acting up. What's yall opinion on this? Advice?
I'm pretty good with soldering so maybe I can re-solder the joints see if it will fix things before replacing the PCM?

Every input is appreciated, thanks.

Screenshot_2025-01-04-01-08-27-88_b9c66f921be6b9ee18febc2ed6906538.jpg

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thump_rrr

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It sounds like you're firing the parts cannon at the car.
I would begin with verifying all grounds and making sure you have no voltage drop across any of them.
Don't forget the ground strap behind the cylinder head.
 

cavero

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I don't see them in your code listed but since you replaced the radio, don't be alarmed if you see "Network" codes. I started getting those after I replaced my radio (car was only a couple years old at the time), I think it was because the factory radio wasn't there to reply to requests over the CANBUS network. But not sure if Torque picks those up
 

nahr123

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It sounds like you're firing the parts cannon at the car.
I would begin with verifying all grounds and making sure you have no voltage drop across any of them.
Don't forget the ground strap behind the cylinder head.
I did not think of the grounds. I will verify the ground locations and report back. Thanks
 

nahr123

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I don't see them in your code listed but since you replaced the radio, don't be alarmed if you see "Network" codes. I started getting those after I replaced my radio (car was only a couple years old at the time), I think it was because the factory radio wasn't there to reply to requests over the CANBUS network. But not sure if Torque picks those up
Hmmm... Yeah I'm thinking of getting a good OBD scanner that works with FORSCAN to see what additional codes there are if any.
 

DieHarder

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I did not think of the grounds. I will verify the ground locations and report back. Thanks
At 13.8 - 14.4v out of the alternator means the grounds appear to be working. As thumper_rrr says if you want you can do a voltage drop test to verify. Simply run the engine and with a VDM on volts DC touch the negative lead to the passenger strut tower ground and positive lead to the body (ground side) of the alternator. If you read any appreciable voltage (.1 to .3v or more) your grounds still need work though at 13.8 - 14.4v that's very close to normal (14.4 - 14.7v).

Have the PCM connectors ever been disconnected/reconnected? If so, you might want to take another look at them for any pins that may be pushed out/misaligned. If they haven't been touched I would try flexing the cables one at a time with the engine running to see if symptoms change. The intermittent nature of your symptoms seem to point to a common issue like grounds being bad or cabling/harness issues or perhaps like you say the PCM but if it were me I'd pay a dealer the diagnostic charge (or someone with a high-end scanner) to help you narrow the most likely suspects instead of throwing more parts at it in the hope you get lucky.
 

nahr123

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At 13.8 - 14.4v out of the alternator means the grounds appear to be working. As thumper_rrr says if you want you can do a voltage drop test to verify. Simply run the engine and with a VDM on volts DC touch the negative lead to the passenger strut tower ground and positive lead to the body (ground side) of the alternator. If you read any appreciable voltage (.1 to .3v or more) your grounds still need work though at 13.8 - 14.4v that's very close to normal (14.4 - 14.7v).

Have the PCM connectors ever been disconnected/reconnected? If so, you might want to take another look at them for any pins that may be pushed out/misaligned. If they haven't been touched I would try flexing the cables one at a time with the engine running to see if symptoms change. The intermittent nature of your symptoms seem to point to a common issue like grounds being bad or cabling/harness issues or perhaps like you say the PCM but if it were me I'd pay a dealer the diagnostic charge (or someone with a high-end scanner) to help you narrow the most likely suspects instead of throwing more parts at it in the hope you get lucky.
Thanks @DieHarder. I will get back with updates during the week
 

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