Hoping to get some help diagnosing the problem i'm having on my '03 F150 supercrew 5.4L. First got code P0443 about a month ago indicating an electrical problem in the evap cannister purge solenoid or vapor mngmt valve circuit. Found a purge valve for low $$ so replaced it....still getting code. Dismounted cannister from back by tank....checked connector and vent solenoid that is mounted to the cannister and seemed ok. Checked power at both solenoid connectors...ok. checked ground at both connectors with key on....ok. Wondering if i'm having a problem with the signal from the PCM....or perhaps the wire/connector to the PCM? Any suggestions would be much appreciated...

 

The CANP valve is under the hood, not at the canister. Which one did you replace?

 

Sorry....replaced the one under the hood next to the brake booster. Does P0443 deal with the CANP valve only....and not the solenoid on the cannister back by the tank?

 

That's correct. The CANV solenoid has it's own electrical fault code (P0446)

Verify switched battery power is present on the RED/YELLOW wire (ignition switch in RUN).

Disconnect solenoid. Check resistance of coil, should be around 34 ohms, +/- 4.

With all power disconnected, check continuity from CANP plug Lt Green/Black wire to PCM connector pin 56.

There are several additional checks to make (short to power or ground), but those are the main ones.

 

Thanks, will check tonight. Before i installed the new CANP valve, i bench tested it with a 12v power supply to see if it would click in and out. didn't hear any clicking when i energized it....just buzzed. Could I have damaged the new one wiht that bench test?? (is it just a simple solenoid coil in the CANP or are there other electronics i could have fried?)

 

It's just a simple solenoid coil.

 

Interesting.....solenoid on new CANP valve seems bad..... 0 ohms. I may have damaged it with my bench test. New one on the way. Will post results when i install. (will skip the bench check this time....) Thanks for your help, Sir.

 

Make certain that you do not have the ohmmeter on an excessively high range. If you do, it will appear as zero, but it isn't.

In any event, if the solenoid coil is indeed 0 ohms (shorted), you will have new and potentially more serious problems.

 

The solenoid is 0 ohms...pretty sure i damaged it when i tested it.

I do have power at the Red/Yellow wire with the ignition switched on.

Took me a while to figure out which pin was 56, but found that and checked for continuity from the PCM connector over to the Lt Green/Black at the CANP connector. It was ok.

So now just waiting for the new CANP valve to arrive and hopefully that solves my woes.

This truck only has 55k Arizona miles on it and never been exposed to corrosion like salt, mud, etc. So i'm hoping the new CANP valve solves it.

 

projectSHO89, I put the new CANP valve in today, went for test drive, still getting P0443 on the code reader. To recap:

- Checked resistance of new CANP solenoid, ok at 32 ohms
- Key on, engine off: 12v power at red/yellow wire in solenoid connector - OK
- All power off, checked continuity between PCM connector pin 56 and grn/black wire at connector: OK

Are there any fuses I should check? Any way this can be caused by a bad fuel cap?

Suggestions for next steps? (really appreciate your help so far...)

 

Did you reset the prior codes before the test drive?

No, this cannot be caused by a gas cap.

If the resistance checks properly and there are no shorts to ground or to power in the CANP circuit, then the PCM is faulty. A shorted solenoid coil may well have damaged it.

 

Yes, battery was disconnected when i installed new CANP valve. Code reader said no faults before test drive. If it is the pcm, what should i expect to pay to replace it? Ok to consider a salvage unit? (lots of them on ebay, i assume they will need to be programmed prior to install?) or would you suggest getting a new one?

 

Anyone with experience having the PCM replaced and what I should expect to pay? Appears my evap system is working fine, just that the pcm does not know it.....since the driver for the CANP valve appears to be the fault.

If I buy a used one, what will it cost to have it programmed/matched to my truck? Any other suggestions?

 

Dealer charged me $100 to reflash after my Edge died during programming.

Plus a tow fee if you're not bringing in just the module.

 

Update: see below