Last post on Dec 25, 2010 at 8:12 PM
You are in the Mazda MPV
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Mazda MPV, Van
#28 of 68 PO174 and PO171 Codes
Jan 05, 2008 (7:46 pm)
I have a 2002 Mazda MPV, 105K - new spark plugs, new wires and new air filter.
But I have these 2 codes showing up (with the following options/hypothesis)
PO174 and PO171:
PO171 - Fuel system for bank 1 is too lean, Oxygen sensor recognized a rich or lean condition on one engine bank only
1- Suspect fuel pressure or Mass Air Flow sensor
2- Oxygen sensor defective
3- Ignition misfire-repair
4- Fuel injector problem
PO174 - Fuel system for bank 2 is too lean, rich or lean air/fuel ratio condition engine bank two
1- Suspect fuel pressure or Mass Air Flow sensor
2- Failed HO2S21
3- Ignition misfire condition
4- Fuel injector problem
Which ones should I ask the mechanic to look at?
I don't want to go back and forth the car shop and just have the CEL keep coming back on...
#29 of 68 Re: PO174 and PO171 Codes [aa0526]
Jan 06, 2008 (2:25 pm)
I think that intake air manifold gasket leak could also cause these codes, so that might be an area to check.
#30 of 68 Re: MPV Error codes P0031 and P0037 [3pawdwolf]
Jan 15, 2008 (1:03 pm)
I could not get anymore info so took it back to mechanic and he replaced the 2 sensors pointed to by P0031 and P0037. After clearing the codes it didn't take long for the check engine light to come back on. The mechanic told me it was back on and still reading P0037- Bank 1 Sensor 2 Heater Circuit Low. He suggested I take it to the Mazda dealership as he wasn't sure what to do except replace more O2 sensors. I don't really fault the the guy.
So I'm out a total of $550 for the 2 visits to mechanic so far (I put this in for the benefit of those who search these error codes in the future)
You folks have any wisdom to share?
#31 of 68 Re: Mazda error code 304 [rafilevi]
Jan 16, 2008 (4:51 pm)
This a frequent problem with 00 Nissan. It has been traced back to intake manifold gasket leak.
#32 of 68 Re: PO174 and PO171 Codes [nls]
Feb 04, 2008 (12:47 pm)
I would take nls's advice. I just had the same codes come up. My regular mechanic guessed it was either the O2 sensors or the gaskets when he saw the readings, but the dealer didn't even hesitate before warning me what it probably was. After doing their own check they confirmed is was the the intake manifold gaskets.
#33 of 68 Re: MPV Error codes P0031 and P0037 [3pawdwolf]
Feb 12, 2008 (6:52 pm)
I know of a 2000 Mazda MPV with the same error codes. The owner took it to the dealer who told them it was the front O2 sensor. They are relatively easy to install with an adjustable wrench or the right size socket ratchet. (Lightening)
#34 of 68 Re: Mazda error code 304 [currier]
Feb 12, 2008 (7:02 pm)
You can buy an OBDII reader for less than $150.00 and delete the code, then sell it before the code reappears. (Lightening)
#35 of 68 Re: MPV Error codes P0031 and P0037 [3pawdwolf]
Feb 20, 2008 (5:27 pm)
I have a 2003 MPV and also got a check engine light that showed P0037. I checked the code at Autozone, and then paid for the more expensive scan at my trusted garage, which returned the same code - "02 Sensor Bank 1 Sensor 2". Same as you, they want to replace one or two of the sensors for nearly $500. I'm hoping you can tell me how you resolved this issue before I throw too much money at it. Is it resolved? Thanks
#36 of 68 Re: MPV Error codes P0031 and P0037 [whyland]
Feb 23, 2008 (8:46 am)
MPV 2001 LX. Check engine light P0031. I have an Actron CP9135 that is 3 years old. It cost $100. It does a beautiful job of reading and erasing codes.
However, it is often difficult to diagnose ck eng lite problems from just the codes. The codes do tell you what parts might be involved, but not to what degree, or in what order, or whether a partial fault in another sensor is cascading to the code in question. With O sensors age causes a decline in performance. Thus you may get an intermittent code that does not always appear immediately.
Note: The two sensors in front of the cats (catalytic converters) are the most important sensors used by the computer for determining fuel mixture. By tracking and responding to these two sensors the computer determines power, fuel mileage, rich/lean conditions which affect the life of the engine and the life of the cats.
The second two O sensors tell the computer how well the cats are working. They determine whether or not you will pass an emissions inspection. Information from these sensors can tell you if your cats are bad. Of course the sensors have to be in good working condition.
Just reading codes will always leave you guessing at what to replace. Even excellent mechanics can only guess at the problem with just a code.
Four months ago I invested in a new code reader. I bought an Actron Elite Autoscanner Pro CP9190. You can buy them online for about $300. Now I know that seems like a lot of money but with the cost of repairs these days it will save you thousands. What is cool and better about this scanner? This scanner gives you realtime readings of the sensor outputs that are coming back to the vehicle's computer.
I am diagnosing my MPV today because it's time for inspection again. Last year I barely passed by clearing the codes then driving the veh about 400 miles until the monitors all registered ready. I got away with that because the veh would run about 700 miles before throwing the OS2 code. This year will be different. Of course last year I did NOT have my new reader (CP9190).
So what does the new scanner tell me that the original one can't? I can now watch a real time graph of the output from any sensor on the car. I can now see that my O2S22 (that's bank 2 second sensor) has a very erratic output. It only operates from about .3v to .7v. Further it's response time is highly degraded. The O2S21 is in great shape running from .1 to 1.1v with a fast response time. Both of my bank one sensors are working well enough not to trigger a code but the are running from .2v to about .8v and they respond slowly to changes in the fuel conditions of the engine. They are close to the end of their life span. That means my engine is running a bit rich, wasting gas, polluting the air, losing power, clogging my cats. If I replace them now (about $100 each) I can save replacing my cats for $2000. Otherwise running too rich will ruin the cats much quicker. Further, because they are near the lower end of acceptable they could also begin to throw intermittant codes as the weather temperurature changes. (other variables will also effect their performance). Why weather changes? Because temperature, air density, and moisture levels affect air/fuel mixtures and their related sensors.
There is a huge advantage to having a scanner which will give you real time readings and graphs of the sensors. Even without any background you can spend a little time comparing sensors and figure out which sensors are under performing. Further you can do live experiments which help in diagnostic. For instance my O2S 22 is under performing badly. with the engine running and the scanner going I unplugged the sensor coupler. The engine continued to run just fine but the scanner voltages went to zero. I plugged it back in and wiggled the coupler to verify contact. With this little test I am more certain the sensor is bad and the wiring is ok.
Another trick you could do with the same set up is pull a vaccum hose off and watch the sensor go low, showing that the fuel mixture is too low. This kind of simple experimentation could help you rule out air leaks. Rev the engine up and down, if the sensor shows good range .1 to .9 and quick response the sensor and the wiring are fine. If is show lean conditions during idle you likely have an air leak.
In a nutshell. Simple code reading will totally leave you guessing, often lead you down the wrong path, and likely end up costing you far more money than it should have cost. For that matter, ANY mechanic that is making suggestions or diagnosis without a real time scanner cannot be giving you your money's worth. Find a friend or mechanic with a graphing scanner.
#37 of 68 Re: MPV Error codes P0031 and P0037 [kprime2]
Feb 23, 2008 (9:39 am)
Thanks Kprime. Good council on how these 02 sensors work and the risk involved in terms of not having to replace one of the cats.