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Mazda Protege Check Engine Light Mystery

I have a 2000 Mazda Protege with 120K miles. I’ve had the car for 13 years and it has been a great car! But, for the past 2 months, the check engine light has been playing cat and mouse - coming on for a few days and then going off for a week and then coming back on. 2 codes have been detected - a P1450 for CDCV valve and PO1170 for a bad front 02 sensor. Our mechanics have replaced the front 02 sensor (on 4/22) and the CDCV valve and sensor (4/30) and just days now after replacing the CDCV valve & sensor and the check engine light is back on!!! Our mechanics thought we might be dealing with multiple problems and maybe we are. One thing that I am starting to realize is that the check engine light is coming on whenever the fuel gauge is showing about a third of a tank left. That has been a constant in the cat and mouse game - which is again proving true as the gas gauge is now showing a third or so full and the check engine light has popped back on. Any ideas? My head is spinning and my wallet is sad!!!

Thanks for any thoughts!

The 1450 code refers to the evap system. There is probably a valve not working, either stuck open or closed. This can result in lean or rich operation sometimes, which could result in an O2 code when there really is no problem with the O2 sensor. Focus on fixing the evap problem first, maybe the O2 code will go away by itself then.

Thanks! I forgot to also mention that for the past 2 months, when I have put gas in my car and then started the car to drive away from the pump that the car almost stalls out. It has never completely stalled out but it certainly stutters and feels like it will.

It’s often the case that when engine performance changes noticeably after a re-fueling, there’s something amiss with the evap system. Problems w/the evap system in modern cars are pretty common, and usually not overly expensive to diagnose & repair.


“Problems w/the evap system in modern cars are pretty common, and usually not overly expensive to diagnose & repair.”

That statement is partially correct, in my opinion

While evap problems are common enough, they’re often not easy to diagnose

I’m not saying it’s impossible. I’m just saying there’s often hard core diagnosis involved, way past tightening and/or replacing a cap.

Unfortunately, some guys don’t have the patience, tools, attitude, information, experience, etc. to tackle these problems.

Evap problems can be among the most frustrating, in my opinion, because they’re often intermittent in nature. That sticking evap purge valve is quite possibly not sticking all the time. And if it’s not sticking when you bring the car into the shop . . .

And the technician also needs to be aware of the various updated parts, pattern failures, TSBs, updated software, etc. out there. And if, for whatever reason, he doesn’t even know where to start . . .

Spend some time talking to professional mechanics, and they . . . if they’re honest with you and with themselves . . . will probably say that evap problems are sometimes the most challenging to solve. Not only that, but they can be among the most challenging to VERIFY the repair. If you want to be sure, you have to see it all the way through. And that’s where some guys stumble. They ASSUME they fixed the problem, release the car to the customer, and it comes back 1 week later with the MIL lit once again, and the exact same fault code.

I’m not condemning anybody, and I’m not saying anybody is wrong

I’m just ranting . . .

Probably the purge valve, which is usually part of the charcoal canister. Sorry you have wasted so much money. Check the Mechanic Files link to find a better mechanic.

@db4690 … informative post, thanks for the correction. Since you have some expertise on this topic, could you offer up some basic info on this question I’ve had but never thought to ask here? My Corolla’s charcoal canister is easy enough to remove from its holder. When I get it on the bench I observe it has three places to connect tubes, two on top, and one on the bottom. The two on the top are pretty clear what they do and how they are connected, one is labeled “tank” and the other is labeled “purge”. But the one on the bottom has no label and seems not to be connected to anything, other than a short rubber tube that is open at the end and as far as I can tell doesn’t connect to anything. What is that bottom tube for?

Without seeing your car . . . and where the caniseter is even located, and its proximity to your tank, etc., I’d not want to make any guesses at this point


@GeorgeSanJose‌, the charcoal canister and evap system for your '92 is a much simpler and easier animal than a 2000 Mazda. The evap system on the Mazda is a complex system with sensors and valves controlled by the ECU. Your '92 basically has a vacuum source and a coolant-activated switch to open the purge circuit ehen the engine is warm. The bottom tube is the vent tube. If the charcoal bed becomes saturated, it can vent excess fumes.

This is a ll great information! Thank you so much! I had suspected the evap valve!! Do you have any information on if an evap valve replacement is an expensive fix and if it is dangerous to drive with the problem or causing any harm to other parts of the car? Thanks again.

Codes don’t tell you about parts. They refer to circuits and systems and provide a starting point for diagnosis. Many shops replace the parts a code refers to, either because they don’t know any better or because it is easier (and more profitable) than diagnosis.

As far as I know, the P1170 is just a low voltage condition on the upstream O2 sensor. The list of potential causes is very long.

The P1450 is an evap system code, and diagnosis is often a total PITA, as noted above. But not matter what, one very common thing is just a leaky vacuum hose. They can be a bear to find, but take about $ .50 worth of material to fix.

Thanks for the info!

as far as evap valves go . . .

There is an evap vent valve and an evap purge valve

Don’t get them confused

The evap purge valve is usually in the engine compartment, and is generally pretty easy to get to

The vent valve is near the canister . . . usually under the car, near the tank, nowadays . . . and is a little more work. In some cases, it’s even part of the canister, and that’s when the part might get expensive

Ok, that’s helpful to know. Thanks again to all!

Would an evap problem impact gas mileage at all or blow a gasket? I had a blown gasket about 2 1/2 months ago before the check engine light started going on and my gas mileage has seemed low these days.

Now that the light is on again, scan the code to see what the new code is.

P1170 is the Mazda version of P0171 (fuel system lean) which is often a fuel pump or mass air flow or ripped air intake boot.

P1450 is evap pressure out of range, (constant vacuum) usually a faulty ECU or shorted wire harness to the fault tank pressure sensor. Voltage checks on the fuel tank pressure sensor circuit will be needed to determine the cause.

“ripped air intake boot.”

Definitely common on Mazdas. I’ve seen it myself