P0300/p0421/p0660

Okay, I am really getting sick of this. Give it your best shot if you have any ideas.

And firstly, yes, I have read basically every thread regarding the poor design of the Protege5 EGR and plug/coilpack setup.

About two years ago, I had a problem with stuttering on my 02' Protege5. I changed the coil packs and wires and cleaned the EGR. Problem solved, though I can't remember which of the two fixed the problem.

Then the stuttering came back, particularly when I was coming to a stop. My car was throwing P0300 and P0421. I waited until the problem got really bad. I drove around with the problem for a good six months, maybe more. As in, stuttering so bad it started stalling out and I had to keep my foot on the gas at stop lights to keep it from dying. I eventually took it to a decent mechanic and we basically just ran the car at idle in the garage and waited for it to happen. The mechanic, not being a Mazda specific guy, didn't see how it could be an EGR, but I told him that the EGRs on our cars were notoriously bad. He went ahead and checked the voltage on the front and rear 02 sensor and they appeared to be functioning properly. He wasn't sure what was going on and I needed the car, so I didn't leave it with him.

I ended up ordering the Canadian recall EGR (with the coolant lines) as well as a cheap eBay cat that I planned to put on so I could pass emissions which were coming up. I installed the new EGR, reset the codes, and noticed no problems for a few weeks. I went and did my state emissions test and looked at the results and I passed with ease. To me, this said that my catalytic converters were still quite good, despite driving around with a potentially faulty EGR for a really long time, which people on the forums said we shouldn't do. This doesn't appear to have fouled up the cats from an emissions perspectiv and if the cats aren't clogged to hell, then the stuttering problem is likely something else otherwise I never would have passed.

Anyway, about a few weeks later, the codes came back, but with an additional one, P0660 regarding VICS. Car still runs fine 99.99% of the time (I'll get to the .01% further down). I checked the connectors that I would have undone to install the new EGR and they all appeared to be connected properly, and I know that a lot of people get this code, particularly on Mazdas, but with even greater frequency on Protege5s than other cars. I looked back at the wires/coils.

I checked the resistance of the two plug wires and compared them to a set of fresh factory plug wires that I had bought for comparison reasons and they were reading exactly the same. Did this with the two coil packs as well, however, because of the nature of our cars, I cannot do a visual inspection for arcing because of how the plug boot sits inside the engine for two of the cylinders. I also didn't have a reliable way to test the resistance of the plugs under actual load and cannot think of a way to do so on this particular car. At this point, the plugs are a few years old and I cannot remember if replacing them the last time fixed the problem or if it was the cleaning of the original EGR that fixed it.

I reset the codes for "fun" and they came back. My car started the running rough once at high altitude (11,000 feet or so on a descent) and the check engine light began blinking, but this stopped after a few minutes and power resumed back to normal, but the three codes remained.

I ask this. What is with our cars? Why do so many of us get the P0300/P0421/P0660? It seems that we suffer from this problem with a much greater frequency than other manufacturers. Has anyone formulated any ideas about what might be causing this? I am leaning toward "maybe" plug wires/coils again and I guess possibly the pre cat, but that is a $700+ part even through mazdaonlineparts and I need to be sure before dropping that kind of wad, plus passing the emissions test so easily makes me think it isn't that.

This is frustrating. Should I take it to a dealership and hock up the $100 for a potentially worthless diagnostic?

Coil packs, wires, and plugs. Change them ($100 from autozone for all 3).

I don't see why driving with a bad EGR is harmful for the cat, the EGR system is recycling exhaust gas which is what cats are made to deal with. Perhaps you're getting confused with driving around with bad coil packs, in that case you don't get a spark which causes unburned fuel to dump into the cat which can ruin it after some time.

Your pre-cat is probably bad, driving around with P0300 (random misfire detection) normally causes P0421 (warm-up catalyst system efficiency below threshold, aka bad cat). P0660 is unrelated (in fact this code doesn't even cause the CEL to illuminate) and means that the VICS solenoid is shot and you'll need to get a new one. It won't affect driveablilty too much since it's only activated above 5000-ish RPM. The part is about $70 from Mazda and takes a minute to replace.

Cool. Thanks for the reply. That cleared up a bunch.

x2 for coils.

Okay. I put in some new plugs, wires, and coils then reset the ECU. We will see if the codes come back.

Any update on the results? I'm just getting the P0300. The car idles a bit rough but it's been hesitating when I'm at cruising speed. At lights decceleration it has also shut off. Any ideas?

the p0300 code is fixed by coil, wire, and plug replacement. Guaranteed, however do it quickly so the unburnt fuel doesnt F*** up your cat like it did mine!!!

UPDATE:

After replacing the coils, plugs, and wires, the ECU wasn't throwing any codes, but the P0421 and P0660 came back. I recently passed a smog test with flying colours, so it would be quite odd if the cat was going bad since it would have likely indicated that, numerically, on the smog read out. I compared the last test results with one I did some number of years prior and it is nearly the same. No symptoms of problems other than these lame codes.

Forgive me for bringing up a dead thread but did you ever get the codes to go away? I am having the same codes pop up in my P5 and losing power once in a while. I have done everything suggested here except the EGR replacament, and i'm saving up to buy new coils. Thanks for the update!

What codes do you have?

Hello all.

Please help me out! :-(
I love my car!

I have a stock 2002 Mazda Protege5. There's no shortage of P0421 threads on this forum but I've yet to find someone who has actually FIXED the issue once and for all.

I've had a P0421 + CEL for at LEAST 3-4 years. Yep, years...but the gas mileage and general performance of the car has remained stable for all this time, despite the CEL and the P0421. Ultimately, it was a horrible idea not to tend to it right away-- but I didn't expect to keep the car this long.

Thing being, I now have to get it smogged, the CEL is getting in the way of doing so. I have a gut feeling that it would pass but you can't smog with a CEL.

Aside from some pinging at 2000RPMs and a bit of struggle on VERY steep hills (pedal all the way down and car has difficulties going up, especially if it's also hot out), the car runs great and idles quite nicely (even from a cold start). It has 255K miles on it and runs very well considering. (Sidebar: I'd love to resolve the pinging noise; tried higher octane already. No additives yet and probably won't go there.)

I just ordered the OEM precat and before I install it, I want to be sure that I've covered all my bases and won't ruin the new precat. I've also heard horror stories about people replacing the precat, O2 sensors, EGRs, etc.--and the CEL and P0421 issues persist. I simply can't afford to have that happen...not financially or otherwise.

Here's what I've completed thus far:
- Spark Plugs / 9-Jun-2012
- Wires / 9-Jun-2012
- Fuel System Cleaning (mechanic cleaned all lines, no additives) / 9-Jun-2012
- Coils (2) / 17-Sep-2012
- O2 Sensor, Downstream only / 19-Sep-2012
- PCV Valve / 22-Sep-2012
- Battery Checked, 12.9V = OKAY / 22-Sep-2012
- MAF cleaning (only) / 24-Sep-2012
- ***UPDATE: Upstream O2 Sensor / 29-Sep-2012


<> ORDERED:
1.) PRECAT - MAZDA OEM
2.) EGR VALVE - MAZDA OEM

<> NEED TO ORDER IF the P0300 and P0660 aren't gone:
1.) VICS (part number is FS05-18-741 )
and
2.) VTCS? Don't know if I really need this...

I've reset/deleted the codes every time I've done a job and the CEL comes back on after some amount of driving (all monitors cleared). Here's a curveball, after resetting, I do get P0300 and P0660 as well but they eventually subside (intermittent, I suppose?). I haven't checked for these codes recently and they MAY have been resolved by the new coils.

I wanted to check and clean the EGR but it's way beyond my abilities. I'm not trained and most of what I've done thus far has been very easy and I've relied on the suggestions of others and knowledge I've gained from this forum.

I paid a pretty penny for the precat and I'm happy to make the investment on other parts, too-- especially if that means I can get more life out of the car and pass CA smog.

What else would compromise the (new) precat? If the EGR was "bad", wouldn't I be getting EGR specific codes?

Has anyone fully resolved this code/associated issues? Again, passing smog is my immediate goal but if I can prolong the life of this great car by doing some other repairs, I'll do it...

Thanks everyone.
NM

^Thanks for the very descriptive and well-written post

Based on all of the things you've replaced I'd say you're almost ready to replace the cat. The pinging and misfire DTCs are quite worrisome and should be taken care of first.

Please try checking the stored DTCs on a regular basis to see if you're still getting P030x codes. I wouldn't replace the cat until I was sure it wasn't misfiring.

Regarding the pinging, the service manual has a section which goes over the possible causes and luckily the list is pretty short. From page 01-03B-33:

• Engine overheating due to cooling system malfunction
• ECT sensor malfunction
• IAT sensor malfunction
• Inadequate engine compression
• Inadequate fuel pressure

Monitor the engine temperature when you notice the pinging (using an obdii scan tool), the fact that the problem worsens when it's hot out seems to point to a cooling system problem.

If your idle is fine, then your EGR valve is fine, don't bruise-up your knuckles trying to clean it for nothing.

P0660 is really simple to fix, your VICS solenoid is broken and needs to be replaced. It's about $70 from Mazda. You should be able to pass your smog test with that DTC because it's not emissions-related. In fact the CEL won't even come on if that's the only DTC present. I wouldn't rush to fix it unless you feel like you're missing some high-end torque

You're right...only the P0421 is in my way on the emissions testing. I updated my long post and also addressed you on another thread. Thanks for being really patient.
NM

I'm providing a summary of this issue because I feel like whenever people do resolve it, they don't come back here to tell you how they did it exactly. So this is for the next poor soul who has to contend with these three codes.


P0421 gone! New OEM precat solved issue. I also passed smog and the icing on the cake = the annoying pinging at 1800-2000 rpm also subsided. As much as I wanted to pass smog, the pinging was a nuisance for a few years now.

P0300 gone! New coils resolved the misfire and you *must* get rid of this prior to replacing the precat. Wish I had fixed this problem right away when the check engine light came on in the first place. I was told today that even a minute and a half of misfiring can kill the precat. Also replaced the PCV...it's $3.00.

P0660 going...when I replace the VICS solenoid valve.

If you replace the precat, I would recommend putting in a new downstream and an upstream o2 sensor regardless.

EGR note: Haven't replaced it or cleaned it. Typically, you'd get DTC (which I never had) for this and my car idles nicely.