Code P0443, bad PCM?

Tiny
JIMRHOUK
  • MEMBER
  • 2010 FORD EXPLORER
  • 4.0L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 190,500 MILES
My vehicle listed above drives great (quiet, smooth, no leaks, etc, ), but the engine light is on. I now live in a state that requires a passing Emission Test, so I've been trying to figure out why the light is on. I've consistently gotten a P0443 error code on the diagnostic tests.

I eventually took it to a mechanic shop and was told that I needed to replace the PCM. I found a business that rebuilds/repairs them, so I sent the PCM to them.

After a few days, I received this response:
"Our tech team is reporting that your unit is non-repairable. Technician’s notes: Hard code (P0443) stored in the processor. The processor Is Not A Component That Can Be Removed / Replaced."

What does it mean when they say, "stored in the processor"? Any advice on what steps I need to take to get my PCM working, and no engine light on, is greatly appreciated.

Thanks for the help!
Friday, March 14th, 2025 AT 6:36 PM

3 Replies

Tiny
AL514
  • MECHANIC
  • 5,073 POSTS
Hello, the processor is the computer (PCM)s main chip or brain on the circuit board. The P0443 code is an Evap Purge Valve control circuit code (P0443 - Evaporative Emission System Purge Control Valve Circuit). Most of the time when a control circuit fails it is the actual circuit driver (a transistor) that burns out and there is a monitoring circuit that branches off which reads the voltage level of that control circuit. It will read a certain voltage level when the Purge valve is off and then a different voltage level when the Purge valve is activated. This is how the PCM can set the code about the control circuit not working. Granted PCMs do fail, so without being able to test the PCM, it's difficult to say how accurate the original testing by the mechanic was. You can try Flagship One for a remanufactured PCM that comes preprogrammed with the VIN number. I would wonder why the PCM failed in this manner in the first place, such as a bad PCM ground or corrosion inside the PCM case. Even a Purge valve that has low resistance could eventually cause a failure, but these computers are designed to shut down certain circuits when an over current condition is detected. I've added the service info on this code as well. I'm sure the company you sent it to had the PCM hooked up to their diagnostic computers and tested the processor to come to the conclusion it had a fault, I like to test the actual pin and wiring that controls the circuit in question for any shorts to ground, shorts to power, along with trying to bi-directionally control the circuit. I don't think the company doing the testing is wrong, but I'm always concerned about why it failed.

Here is a link to Flagship one and your 2010 Ford PCM:

https://www.fs1inc.com/ford-lincoln-mercury.html?make=96&model=66&year=126&enginesize=463
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Friday, March 14th, 2025 AT 8:06 PM
Tiny
JIMRHOUK
  • MEMBER
  • 2 POSTS
Thanks. The frustrating thing is that the car has no leaks or rust and drives like a dream. The only hint of an issue is the engine light, which I'm okay with, if I didn't have to pass emissions. Are there any options for finding and replacing the transistor in question?

I think my next car will be from the 1970s!
Thanks again!
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Saturday, March 15th, 2025 AT 11:48 AM
Tiny
AL514
  • MECHANIC
  • 5,073 POSTS
Well, the transistor that controls the Purge Valve is, in turn, controlled by the module's processor which they have ruled as faulty, so in that case replacing the module is the only option. It's always a difficult call to make when modules fail, I would just make sure the original mechanic checked the purge valve and its circuits. The Purge valve is part of the emissions system used for pulling fuel vapors from the gas tank, so it needs to be functioning to get a new emissions sticker.
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Saturday, March 15th, 2025 AT 4:21 PM

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