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Q: check engine light will not go off on 2000 Mazda B4000

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2000 Mazda B4000 Pickup - replaced all upper and lower oxygen sensorS, replaced the gas cap and the mass air flow filter and the check engine light will not go off. Truck runs great but gas mileage is bad. What else could it be. I would like to do something to improve gas mileage since that is why I bought a small 6 cylinder pickup, Ford Rangers with theis size motors get almost twice what this truck gets.
Wow. I would have definitely advised to actually check the vehicle out prior to replacing all those unnecessary parts.
I suspect your problem is an intake manifold leak. The o-ring gaskets (SOHC engine?) are notorious for leaking, causing lean codes and a check engine light. Whoever advised you to replace all those parts really led you down the wrong path.
Code P0174 -
Lean Air/Fuel ratio bank 2
Low fuel pressure
large vacuum leak
dirty/defective MAF sensor - have replaced this
engine mechanical condition

Should I take this 2000 Mazda B4000 pickup to the local Ford Dealer for diagnosis (100.00 cost)? I have nearly $400 in trying to fix this problem since November 2010 or find a Mazda dealer in Dalls-Ft. Worth area?

Thank you for your time and help in responding quickly.
Did you use original equipment Mazda / Ford parts for the oxygen sensors. I suspect you have a bank 2 pre-cat oxygen sensor that is not working right. Either the wiring is faulty (many aftermarket sensors have generic connectors), or the sensor itself is not functioning right.

A diagnostic test monitoring fuel trims will help diagnose the problem.

It is NOT a MAF sensor failure or a vacuum leak because only one bank is affected.
My B4000 needed a fuel filler hose; the original rotted at the connection to the tank. Mazda cost was $350+; on-line for $90. Remove the truck bed (pretty easy) with a T-55 tool for the 6 hold-down bolts and slide the bed to the rear to expose the tank. Don't forget to remove the screws holing the gas cap bezel to the body first. Examine the filler hose for rot.
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