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david, Auto Service Technician
Category: Ford
Satisfied Customers: 1500
Experience:  Certified Master Technician,Certified in diesel & gasoline engines
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I have a 1998 Ford Taurus 3.0L OHV. Trouble code PO443 ...

Customer Question

I have a 1998 Ford Taurus 3.0L OHV. Trouble code PO443 continuely shows. The EVAP purge valve solenoid has been replaced, also the EVAP canister vent solenoid. 12 volts at the purge valve, and resistance at computer pins 56 and 71 check out. What do I do NOW??

Submitted: 11 years ago.
Category: Ford
Expert:  david replied 11 years ago.

thank you for the question hope this helps.

Most likely, it is a corroded or damage wire or connector. It is also possible that the PCM has a failure.

Here's the list of possibilities
VPWR circuit open
EVAP canister purge valve circuit shorted to GND
Damaged EVAP canister purge valve
EVAP canister purge valve circuit open
EVAP canister purge valve circuit shorted to VPWR
Damaged PCM

The Evap system monitors flow with the O2 sensor readings. When your Evap purge Solenoid cycles and the evap system flows, the PCM knows that the O2 sensors are going to react accordingly, and if they don't, the PCM will assume the evap purge solenoid is not functioning or that there is a leak in the vacuum line between the intake and the canister, and is causing the evap system to suck air not gas vapor. This will cause the O2 sensor to actually respond backwards to what the PCM knows it should. That is what sets the code.
The most common problem I have seen is cracked rubber hoses, Especially at the top of the hoses at the canister you can't see. Feel for cracks on the hoses where you can't see. Also check the Evap purge solenoid vacuum supply line at the solenoid. Make sure you have vacuum there.

good luck if this is not it i can help more

Customer: replied 11 years ago.
Reply to david's Post: I've checked all hoses at the firewall mounted EVAPpurge valve, also the trunk mounted EVAP canister. All are good.The Helm shop manual states DTC PO443 only checks elec.curcuit for the EVAP purge valve.Codes442 and 455 monitor vacuum. How do I verify the PCM as the problem? Following the pinpoint tests HX10 thru 15 lead to FlashEEPROM. Thank you! Any help is appreciated.
Customer: replied 11 years ago.
Relist: I still need help.
I have a 1998 Ford Taurus 3.0L OHV. Check engine light comes on all the time with DTC PO443(EVAP canister purge valve circuit malfunction) The EVAP purge valve has been replaced. VPWR circuit has 12 volts,resistance at PCM pins 56 and 71 checks out fine. Also the EVAP canister vent solenoid has been replaced. I can find no broken or corroded connections. According to the Helm shop manual the final solution is to replace or flash the PCM. HOW DO I DETERMINE THE PCM IS AT FAULT??