Hi,

My car failed DEQ: failed THC g/mi MAX and CO g/mi MAX. When I drive the car the check engine light came on and stayed on until I turned off the car.
I've then replaced Engine Coolant Temperature Sensor, Oxygen Sensor, and Mass Air Flow Sensor (told by the mechanics).
Now my car's check engine light comes on when I accelerate (press gas), but it goes away when I stop pressing the gas paddle.

Can you guys help me solve this problem?

Thanks in advance.

 

Where did you go to check your car, were you throwing those codes and thats why you had to change all those sensor's?

 

Hi Tbird,
I was told by the Auto Zone mechanics. They compared the diagnostic codes to the manual and I replaced those parts. I can't remember the codes, but I'm sure that those codes according to manual relates to the parts I've replaced .

 

Does your 94 626 have the auto or manual trans vtriniti? Have you since passed the emissions test and what code number is now being stored? Sounds like a possible throttle position sensor problem.

 

Hi babyhuey,
My 94 626 have auto transmision. After replacing Engine Coolant Temperature Sensor, Oxygen Sensor, I went to DEQ and failed THC g/mi MAX and CO g/mi MAX emission test.
The car runs fine, and somebody is already driving it. I will get the diagnostic codes asap.

Thanks babyhuey.

 

Do not replace anymore sensors untill we have looked at the problem ok

 

Hi babyhuey,

I drove to AutoZone this morning and the check engine light came on and stayed on instead. This time I got the same code again 172 from the AutoZone mechanic. The mechanic called a emission specialist and the speciallist said that he had the same problem with this car model that its computer keeps sending out the same codes, and he suggested to update the computer or reprogram it at a mazda dealer shop. But I want to wait for your advice on this one.

Thanks babyhuey.

 

Yea man,waiton that ****, wait to see what baby says im pretty sure he will hit you back with something usefull. You know what you might do is take it to an actuall car specialist and have them run the diag.. they will to that right and find out what they say, get two opinions on that matter cause autozone sucks dood. they might charge you like 30 bucks but its usefull.

 

I am not aware of any calibration changes and am not even sure that the PCM in your 626 is programmable. Seems like 96 was the earliest that calibration changes were possible. P0172 is telling us that the Oxygen sensor is not switching and is indicating a lean condition. This would explain your emission failure as the computer is compensating by running the system richer and richer. I am surprised that you have not also stored a P0181 ( Adaptive fuel control rich limit reached at part throttle, system lean). That would be why your CEL only came on with foot on the gas and not when pedal released. Would bet that Autozone did not run a Key On Engine Running self test but only did the Key On Engine Off test. P0181 would only be output with the KOER test and not KOEO although the P0172 would.
You said that you replaced the oxygen sensor so we will have to assume that the output signals are accurate and actually indicating a lean condition. Two things to check.

First and most important is the Mass Air Flow sensing wires. Very common problem for them to get coated with black soot and send an inaccurate air flow signal. Lower than actual in this case. You will need to have a tamperproof T-20 Torx bit to remove the sensor from the top of the air cleaner housing. When removed you will see two posts in the tip of the sensor. Between these two posts are set two short wires with a bulge in the middle. These are the air flow sensing wires. Now look at the side that would have been facing toward the engine side. Posts and wires will probably be very clean and bright silver is color. Now look at the side that would have been towards the air cleaner and in direct path of intake air flow. If that side is black, fuzzy looking, or any other sign of contamination that would not have it looking like the other side then you have found your problem. The PCM sends and measures electrical currect thru these wires and trys to maintain a constant temperature at these wire. The more air flow, the faster the wires cool off and the more current needs to be sent to maintain that temp. Sooty build up acts as a sort of "Winter Coat" if you will and insulates the wires from measuring this flow accuratly. They are very often cleanable to repair although sometimes it does not work. Clean with good close blasts from a can of non-clorinated brake parts cleaner untill clean and shiny silver. Allow to air dry and reinstall to air cleaner. Be carefull not to touch them or use anything to try and scrub. They are very delicate and easily break when touched. Know that one first hand. Disconnect the negative battery cable and step on the brake pedal for at least 30 seconds to clear codes and reset fuel trim levels to factory zero.

The other thing to look for if above all looks ok are vacuum leaks. Intake manifold gaskets are not uncommon either on this engine and will create same problems. Ideal situation would be to use a digital volt meter to actually look at the oxygen sensor output voltage and see what it is doing. You do not by chance have one or would be able to get hands on one would you? Invaluable tool for working on later model cars with all of the electronic and fairly decent can be found at Radio Shack for as little as $20.

Good luck in your checking and let us know what you have found out vtriniti.

 

I've replaced the Mass Air Flow Sensor including the housing part with new sensor and housing part. But does that fix the problem from mass air flow sensing wires?

About messure the voltage from oxygen sensor using the digital volt meter, how do i messure? Have the sensor connected to digital volt meter and Key on engine off?

I'll ask the mazda dealers about the calibration changes/PCM updates for this car.

Thanks babyhuey.