I have a 98 F150 5.4 and recently after a dealer trip to get tranny filter changed I got an error code p0443. I had the dealer look at it and his response was that it needed a new PCM because the PCM was not outputting ground to the purge canister valve. Occasionally it will generate a p0455 code with it for a Large evap leak. The engine still runs fine with mileage near normal. I assume this dealer is on beans. Should I just replace the purge valve its only like $50. Or do you think this guy may be right. It just sounds odd if the pcm was gone I would get more errors.

 

The dealer is NOT on crack. A faulty PCM is just one of the possibilities for causing a P0443 code.

However, without knowing exactly what diagnostic steps the dealer tech may have performed, I will only point out the possibilities:

Open CP valve solenoid coil
Open power circuit to CP valve
Open signal line to CP valve
Signal line shorted to either ground or power
Faulty PCM output driver or sense circuitry

Personally, I'd pull the valve and measure the coil resistance to see if it's open. I'd also pull and inspect each of the inline connectors for corrosion, especially under the cab.

The factory PCED has the prescribed diagnostic procedure for finding the problem.

Steve

 

The dealer said he did a "pinpoint diagnostic" . There was really no other info than that. It just seems odd that the first recommended fix would be the most expensive item. I'm sure they won't refund me if the pcm doen't fix th problem.

 

Get the estimate in writing and get a written assurance that any repairs made will be effective.

Unless you have to have an emissions test for licensing purposes, this fault won't have any effect on the truck's drivability.

Steve