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Drew, Super Mazda Tech.
Category: Mazda
Satisfied Customers: 2518
Experience:  19 yrs. experience. Mazda Senior Certified Tech, with Ford, Linc. & Merc. experience. ASE L1 Advanced Certified Master Tech.
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1997 Mazda B4000: has returned error codes p0171 and p0174..leaks

Customer Question

I have a 1997 Mazda B4000 that has returned error codes P0171 and P0174. How do I fix these errors? I've found several places that say that I need to check for vac leaks but I don't know how to do that either. Also my switch for switching between hot and cold air temp is not switching which is also a vac I believe. How would I fix that?
Submitted: 6 years ago.
Category: Mazda
Expert:  Drew replied 6 years ago.

Hello. My name is XXXXX XXXXX I will be glad to assist.


These two codes indicate a lean condition. This is usually caused by a vacuum leak. Inspect all vacuum lines and PCV valve. Listen for vacuum leak.

Drew and 7 other Mazda Specialists are ready to help you
Customer: replied 6 years ago.
I'm not sure what vacuum lines I'm checking. Maybe I selected the wrong option but I'm assuming that is also why my hot and cold air selector switch does not work also. Is that a safe assumption?
Expert:  Drew replied 6 years ago.

That is very possible. With the engine running, listen for a hissing noise. You can also use starting fluid or brake cleaner to spray in areas of the engine, If there is a vacuum leak, the engine will suck up the starting fluid and change RPM or stall.


Most vacuum hoses are black plastic or rubber.

Customer: replied 6 years ago.
Was I correct about the hot and cold switch also?
Expert:  Drew replied 6 years ago.

There is vacuum supply to the heater control but if vacuum supply to the heater control was missing, you will only have defrost mode. Check the small vacuum line, under the hood, that goes through the fire wall, by the heater box on the passanger side of the truck. Under the glove box is a connection. Make sure you have supply vacuum there.


On the upper intake manifold, drivers side, againt the fire wall is a "T" fitting with lots of vacuum lines connecting there. Inspect for broken/damaged lines.

Drew and 7 other Mazda Specialists are ready to help you
Customer: replied 6 years ago.
Expert:  Drew replied 6 years ago.

Your welcome. Please let me know I your have any other question. I would also like to know your results of testing and what you found with your vacuum line inspection.


Thanks for the accept again.


Drew Cool