Check engine light

Replaced O2 senser at 25,000 miles. At 36k
light back on, goes off after fillup and back on after 10 miles or so. Failed Maryland state
emisions test, told O2 senser bad, bank 2 #1
Had replaced and light reset, light back on in less then 10 miles. Toped off tank today and light goes off, could this be a faulty gas cap.
Has any one had ths problem. O2 sencers aren`t cheep, have been told i may need to replace all 4 (ouch)

Faulty gas caps can lead to check engine lights on these newer fords.
It would greatly help if you could retrieve the code that the PCM has set
to trigger this light. If it does show that the 0xy sensor is causing, that does not necessarily mean that a new one will fix the problem.
It could be a vacuum leak if it is lean, etc.

Keep me posted.

Good Luck

Thanks Fordman123
The only info i have is the diagnostic report
from the failed emissions test.

MIL Engine Off: PASS
MIL Engine ON: FAIL
DLC Tampering: PASS
OBD11 Communication: PASS
MIL Command Status: FAIL
Fault Codes: P0156 O2 Sensor Circuit Malfunction (Bank 2 Sensor 2)

The shop that installed O2 downstream sensor charged $60.00 for computer diag.
Dont know if this is true or he used info i gave him (see above) He says he`ll reset
the light for free (ha. hes got my $250.00
and a very unhappy coustomer)

If the above code is not what your looking for i can check back with him and see what if any codes he can give me.
(:-) my $60.00)

Should i buy a diagnostic code reader, as i also own a 2002 F150 and hope to keep both vehicles as long as possible

Fords forever Tim

The gas cap will cause the check engine light to come on for sure. If you go to auto zone they will check your codes for free and tell you exactly whats wrong.

I had a 95 Windstar tried everything find why the check engine light stayed on, then almost 1 year later as I just left it on and gave up.

one day I noticed a rubber hose was leaking exhaust, located at right side of motor around the EGR vale, the rubber hose dried out and had cracked.

I replaced the hose and took off the + batterie post cable for a few minutes to reset the check engine light to go off, and the check engine light never came on again.

Hope this helps

Cheaper bad brand of gas can do that I switched Amoco 87 Octane, 5000 miles ago and the problem has gone.

Are you getting a check engine light? I had an issue with the engine running lean. Turns out Ford has an issue with the way the fuel injection is "gasketed" to the engine. The o-rings leak and cause the engine to run lean.