Mechanics

CHECK ENGINE LIGHT CODES 174-175

2001 Mazda 626

Computer problem
2001 Mazda 626 6 cyl Front Wheel Drive Manual 75200 miles

Yes, very low mileage, mostly city/some highway.
Codes 174-175 mean 'rich fuel mixture'. Mechanic kept car for week to replace air filter/MAF sensor. Light came back on after one day. Per Auto Zone suggestion; put in expensive fuel injector cleaner. Light stays off for 300 miiles. Repeat cleaner with fill up. Light stays off for 200 miles. Repeat cleaner with fill up; light stays off for only 50 miles.

I need this car to pass inspection now, what can I do? Does this very temporary fix suggest a specific problem? Replace a fuel injector? Which one? I'd gladly follow another temp fix to get light off long enough to pass inspection that is now required in November.
OH, one more thing, I have to add coolant once per month? Or so, no leakage on driveway, but reservoir is empty when I check it. Car DOES seem to run just fine in all conditions, temp guage never gets 'hot'.

As much info would be appreciated as I don't trust the knowledge of this mechanic, although he's fair with his pricing/very thorough with more simple maintenance/oil& brakes etc.
Avatar
PaulyMan360
October 16, 2009.




FUEL SYSTEM MONITOR SERVICE TIPS
P0171, P0172, P0174, P0175: These DTCs are not likely caused by HO2S failures. The majority of HO2S returned under warranty for repairing these DTC's are found to be functioning normally. Additional related DTCs are usually present when there is a concern with an HO2S. These DTCs are never the result of a problem with a down-stream HO2S. Always look for a condition related to the rich or lean failure.
Lean Conditions & Vacuum Leaks (Un-Metered Air): Suspect a vacuum leak if the Freeze Frame Data indicated the fault at idle or low speed. The MAF sensor signal may drop below normal and the Idle Air control may be operating at its upper limit. A lean condition can be caused by un-metered air leaks (leaks between the MAF and the intake manifold). Examples of possible leaks are: loose, damaged vacuum lines, intake manhifold gaskets or o-rings, throttle body gaskets, brake booster hoses or diaphraghm, air inlet tube, stuck or frozen PCV valve, unseated engine oil dip stick, partially blocked air filter or MAF inlet.
Lean Conditions & Insufficient Fueling: Suspect a restricted fuel system if the Freeze Frame Data indicated the fault at high engine load or throttle position. Restricted fuel concerns will usually be more apparent at high engine load and may be accompanied by concerns of lack of power or poor acceleration. Checking fuel pressure under load is a good place to start. Examples of possible causes of low fuel pressure or fuel starvation are: weak fuel pump, plugged filter, fuel leaks, restricted fuel supply line, contaminated or plugged fuel injectors.
False Lean Conditions / Exhaust Leaks: A leak around the HO2S will cause the PCM to sense a false lean condition. This can be caused by leaks upstream near the HO2S or by secondary air malfunctions

DTC P0171 is set when right bank fuel trim system is too lean. DTC P0174 is set when left bank fuel trim system is too lean. DTC P0172 is set when right bank fuel trim system is too rich. DTC P0175 is set when left bank fuel trim system is too rich. DTC P1130 is set when right bank fuel control system has reached maximum compensation for lean or rich condition and front heated oxygen sensor HO2S is still not switching. DTC P1150 is set when left bank fuel control system has reached maximum compensation for lean or rich condition and front heated oxygen sensor HO2S is still not switching. P1131 is set when right bank fuel control system is correcting rich for an overly lean condition and front HO2S voltage is less than.45 volt. P1151 is set when left bank fuel control system is correcting rich for an overly lean condition and front HO2S voltage is less than.45 volt. P1132 is set when right bank fuel control system is correcting lean for an overly rich condition and front HO2S voltage is more than.45 volt. P1152 is set when left bank fuel control system is correcting lean for an overly rich condition and front HO2S voltage is more than.45 volt. Possible causes are: Excessive fuel pressure.
Leaking fuel injector.
Leaking pressure regulator.
Low fuel pressure or running out of fuel.
Contaminated fuel injector.
Oil overfill.
Incorrect cam timing.
Incorrect cylinder compression.
Exhaust leaks up steam of, or near HO2S.
Air leaks between Mass Airflow (MAF) sensor and intake manifold.
Vacuum leaks.
Restricted air inlet.
PCV system malfunction.
Fuel purge system malfunction.
Improperly seated engine oil dipstick.
Leaking EGR valve gasket.
Stuck open EGR valve.
Leaking EGR valve diaphragm.
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BMRFIXIT
Oct 17, 2009.
Both indicating RICH fuel mixture. I don't have original receipt from mechanic, I may have misspoke of 174/175 as they contradict each other. I do remember each code meant RICH.

As I said, car runs great, in fact I just put in MORE fuel injector cleaner with 5 gal gas, car is getting 24MPG city, best I can remember in a long time.

Does adding coolant consistantly contribute to this problem?
Does temp fix of fuel inj cleaner indicate a fuel injector problem?
Any other temp fix you know of that can help me?
Can driving with this condition open me up to more damage/repairs in future?

Tiny
PaulyMan360
Oct 17, 2009.
Thank you for your negative feed as I am trying to help you
if you think I have a magic stick that I can wave to fix your car
you are for sure wrong
if you read what I sent you and willing to do some checking you will find your problem
keep adding all the fuel injector cleaner that you can buy is not going to fix your problem

what I sent you is TSB
that most tech love to get their hands on

BMRFIXIT
Oct 18, 2009.

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