I've had a problem with my car since about November-December. My CEL will come on for a couple days and go off for a couple more. I had a OBDII tool and checked the code, P1170, for the front O2 sensor. Hoping it would be as simple as that I just went and replaced it. That didn't solve my problem..

So I've let this problem continue for several months, I don't see any noticeable vacuum leak symptoms. It idles fine, maybe SLIGHTLY unstable when at a light. It feels maybe just a bit sluggish accelerating, but that could easily be my imagination.

But I've pulled the freeze frame data several times that it's thrown a code and the LTFT is always +25, STFT always 0, always in open loop due to a fault, and it always comes on at cruising speed (80 km/h and up).

From what I've read online the most likely thing that could be wrong is with the vacuum system, which I'm going to check on monday. But I'm also wondering if you think that this points to any other issue I'm not seeing here.

And I have a '01 protege, SE, 1.6L. If you need anything else let me know, thanks.

 

Un,

Check these items for vacuum related problems:

1. Air intake hose between air filter and throttle body for cracks. Make sure clamps are tight.

2. All other vacuum lines.

3. Throttle body and intake manifold nuts/bolts for tightness.

4. MAF sensor - has it been cleaned recently?

5. Cracks in the exhaust manifold.

Hope this helps out. I've had #1, #4 and #5 on my 99 with the 1.6.

J

 

Thanks for your suggestions! Today I thought I would just clean the MAF sensor, turns out it was covered in what appeared to be soot, whatever it was it was black and coated the sensor part. I cleaned it up nicely and took the car for a test drive...
No luck though, I was able to get it to throw a pending P1170 code again.

However, I did notice this hose coming out of the main intake going into the engine block (possibly not the right name).. it looks terrible and very deteriorated. I'm going to try and inspect the hoses for vacuum leaks tomorrow, but that hose cannot be normal, right? And if I should get that replaced, where would I go about finding it? Would I have to visit the dealer? It looks like something that would be model-specific

 

Hi again Un,

After looking at your reply and doing some quick research, here are some additional thoughts/ideas. Pardon if I get into things you already know, just trying to be thorough...

This code indicates that the front O2 sensor is not seeing a normal "switching mode". In normal operation, the 02 sensor output voltage to the computer oscillates between 0 and 1 volt, depending on quantity of unburned oxygen it is sensing at a given time in the exhaust stream. Ideally, the engine computer likes to see around 0.45 volts from this sensor, so it continually tweaks the injectors "on" period to maintain this average as the engine runs. In your case, the 02 sensor is reporting on the high side of the optimum (adding additional fuel) for a period exceeding approximately 43 seconds. Here is the direct quote from the 2002 service manual for this code:

DTC P1170 HO2S (front) no inversion: PCM monitors input voltage from HO2S (front) when the following monitoring conditions are met. If input voltage from sensor remains below or above 0.45 V for 42.9 s, PCM determines that there is no HO2S (front, RH) inversion.

MONITORING CONDITIONS
— Engine speed is above 1,500 rpm.
— Engine coolant temperature is above 80 °C {176 °F}.

Some of the possible causes (also from the manual) are as follows:

HO2S (front) malfunction
• HO2S (front) heater malfunction
• Fuel injector malfunction
• Pressure regulator malfunction
• Fuel pump malfunction
• Fuel delivery hose clogging or leakage
• Fuel filter clogging
• Fuel return hose clogging or leakage
• Air suction or leakage
• PCV valve malfunction
• Purge solenoid valve malfunction
• Purge solenoid hoses are hooked up incorrectly.
• Ignition coil malfunction
• Insufficient compression
• Engine malfunction

In your case, your LTFT is saying that it is trying to compensate for what appears to be a lean condition, so your search for a possible vacuum leak is valid. I am curious that the computer hasn't reported any running lean codes such as P0171 or something like that. However, some of the other possible causes listed above need to be looked at. One of the simpler items above to check is the PCV valve - has it been serviced in the last 50K miles (including the hose that connects it to the intake manifold)? How about the fuel pressure? - have you checked it as well? Go for the simple stuff first- check all them darn hoses then work your way up.

As far as the plastic connector in the picture - yeah it looks degraded. Could be a possible issue. The small hose coming off it goes to your valve cover and supplies intake air to the PCV system so the air route is from the big hose through the little one and back out through the PCV valve into the intake manifold. I looked at a parts list for the 1999 year, but it doesn't show that plastic piece a separate part. It is serviced as an assembly with the larger hose. FYI - the larger air intake hose part # from this parts list is ZM01-13-220. This number may be superceded by a newer number so check with a dealer if you decide that this larger hose should be replaced.

Speaking of the larger hose, when you pull it off and inspect it carefully for any cracks, pay particular attention to the bellows or riffled area. Mine cracked in this area. If you find this, don't try to patch it - just go get a new one. If it is OK, you might be able to find that plastic connector for the smaller hose from a junkyard.

As far as the 02 sensor you replaced - was it a direct replacement or did you have to splice onto the original connector? I assume it the direct replacement type.

One other thing to look at that I had happen to me - closely inspect the hose that comes off the intake manifold and connects to the brake booster. Specifically, look at the intake manifold side of it. I had a small crack in that hose that drove me nuts until I found it. A real pisser..... BTW - if you find a problem with that hose, be advised that it has a vacuum check valve in it (at least the one in my 99 does). If you put a standard hose there, you have no power assist if the engine is off unless Mazda got smart and put a separate check valve on that year vehicle.

Anyway, I hope this helps you in your quest. I will monitor your progress and try to help as best as possible.

J

 

Thank you so much for your help!

I think I have found my problem though. That connector in the picture is the problem, I pulled it off today and I could easily blow air through it while blocking one end. I'm going to go to the dealer tomorrow and see what part I'll need to order. Unfortunately I also cracked the connecting hose when putting it back on, I guess it's just brittle from age.

However, being a total novice with car stuff, I thought that was the pcv valve, and bought a new one... So I wasted $5 but I just took out the old one, which didn't look too bad, and replaced it.

And just to answer one of your questions, the O2 sensor was a universal one that I just spliced together using the provided connecting pieces.
Also, it has not reported a code (at least any time I've checked) other than the original one, P1170. I'm guessing because the leak isn't very big..

 

Un,

Great to hear that it may be that simple! I hope that fixes your problem and glad to be of some minor help. If, by chance you still have similar issues later, look at all the other vacuum hoses described in my earlier posts as well as verifying that the 02 sensor is wired properly.

I believe the part number for that smaller L-shaped vent hose is ZL01-13-742. It cost me about $6 from an online OEM parts supplier out of Washington state.

Also - the PCV valve wasn't a wasted cost-it was probably due..... One more item - make sure that the rubber grommet that you pushed the PCV valve into wasn't deteriorated as well - just another possible place for unwanted air to sneak in..

Happy Trails...

J

 

Would you by any chance still happen to have the website you bought the part from?

 

You bet:

Walkers Renton Mazda | New Mazda dealership in Renton, WA 98057

cost was $6.06 plus freight. I ordered a bunch of other stuff along with it, so freight will vary.

Here is another site that has that vent hose a little cheaper:

Mazda Parts Center - Call (800) 650-4896 for up to 30% Off on Genuine Mazda Parts and Accessories

Any idea how that plastic connector got nuked? Never seen that before...

See Ya,

J

 

Thanks for the links. I did just end up going to the dealer this morning and ordering them. Wasn't too much more expensive.. $54 total, and they should be there tomorrow.

And how that connector got so degraded.. I have no clue! That's what I'm trying to figure out.. Maybe it was the stuff I sprayed on the battery terminals to prevent the massive corrosion that was going on, but nothing else around it is eaten away.. I'll post a pic tomorrow of the underside of that piece just for curiosity, it's even worse..

 

Ugh... So I put the new air hose and vent hose in and went for a test drive... It still throws a code..

I want to check the exhaust manifold now. But how should I go about doing this?