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97 MPV CEL with P0420 Code

Old 02-01-2008, 12:41 AM
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Join Date: Jan 2008
Posts: 3
Default 97 MPV CEL with P0420 Code

Thanks for such a great forum. We bought a used 97MPV 4x4 All Sport this October and have loved it. It has 110,000 and had been mechanically and imaculately maintained by the previous owner. This last Nov. just before leaving for Thanksgiving the CEL came on a day or two after a fuel fill up.

The sales person at Autozone did not show me the code when I had it scanned. He said that it was an easy one and the asked if I had just put fuel in the vehicle?Explainingthat the gas cap was probably loose. Relieved that it was an easy fix. I tightened the cap and he cleared the code. We went on our trip up into the mountains for Thankgiving without any worries.

About a month later with a half tank left on another fill up the CEL came on again. Autozone scanned it again and another sales person reacted to the code "by the book" and printed off the receipt giving me the code, P0420. And proceeded to price out the possible components to fix it. She also explained thatshecould not reset the CEL light until there had been an attempt to fix the problem. I thanked her and took theprintouthome. The following is the description on the receipt.

Definition: Catalyst efficiency low-bank 1.
Explanation: The oxygen sensors monitor the catalytic converters ability to store oxygen. Possible Causes:
1. Catalytic Converter defective (failure possibly due to #2, 3, or 4)
2. Engine misfire or running condition.
3. Large Vacuum leak.
4. Engine oil leakage into exhaust-valuve guide seals, piston rings.

I disconnected the battery thinking it may be a fluke with the cap again. Well, another fill up and a half tank laterthe CELcame on again in January. I have not bothered to clear it by disconnecting the battery yet.I had mentioned this problem to the emissions technician at the first of January after I had received a passing inspection. Hetold me that henoticed something a bit abnormalduring the test, but it appearently did not affect things enough to not pass the emissions test. At the time the CEL was not on and he mentioned to me that I could bring it back if the light came on and he would take a look at it.

I'm new to this vehicle and don't own the Chilton's manual yet, though I intend to buy one. I do alot of the work on my vehicles myself. Does anyone have suggestions where I should begin with a possible fix.

Research I have done online has told me about the loose gas cap, O2 Sensors are bad,or thatO2 sensors usually never fail, and that the expensive Cat. Conv. needs replacement. And if I don't fix this, with the engineburning rich the Cat. Conv. will fail and there maybe a possibilty for a firein the exahust system on the side of the road some day.That sounds pretty bad....Don't want that to happen.

BabyHuey, I have appreciated your responses on this forum. Your advice and opinions of the older MPV's helped pursuade us that we were making a good purchase (My wife did not want a Minivan). Please help with any advice you or others might have on the P0420 code. We plan to keep this vehicle for a long time. We paid cash for it and love the idea that we hopefully would not be putting alot of money into future maintence and fixes. Our other mazda...A 1992 protege with 123,000 miles that we have had since new.... has never given us any major mechanicalproblems. (I think it needs a spark plug, rotor, fuel filter tune up. It has a rough acceleration, that is for another post though.)

Thanks in advance for any advice passed along.
Old 02-12-2008, 12:28 AM
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Join Date: Jan 2008
Posts: 3
Default RE: 97 MPV CEL with P0420 Code

Just checking in since my original post.

I decided to not clear the P0420 code artificially by disconnecting the battery cable for the perscribed 30 minutes or so. Instead I took it on a trip to the mountains this last weekend and the Check Engine Light cleared after about 45 miles of driving up the canyons.

Did this exercise of driving long distance clear and reset the computer by buring off whatever was in the Catalytic Converters that cause the difficiency codes? If so, should I expect that the computers are operating the vehicle in "optimum performance"?

The mileage for trip odometer since the last fill up 172 mile and I filled up again with 10 gallons. About 17 miles per gallon for driving around town and up into the mountains this past weekend. Not bad but would still like to see that number improve some more. I'll be curious to see what the mileage per gallon is for interstate travel.

Please post a reply if you have anyadvice orthoughts.

Old 03-04-2008, 03:13 PM
Join Date: Nov 2007
Posts: 3
Default RE: 97 MPV CEL with P0420 Code


I am disappointed that no one has replied to your post. I have a 98 4x4 All Sport with 120k miles that has the same problem as yours.

I don't think it is the gas cap or fuel system...although the purge relay (pass. side firewall) makes a very loud clicking noise at startup.

I bought a pair of new O2 sensors and plan to replace them when the weather permits. It won't hurt to do so...and if the CE light comes on again, then I know the problem is with the catalytic converter. Many others on the site (and the MPVClub website) have had success just changing out the rear O2 sensor so that's the first step.

Let us know if you make any other changes, OK?

Old 03-11-2008, 12:01 AM
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Join Date: Jan 2008
Posts: 3
Default RE: 97 MPV CEL with P0420 Code

DesignProf, I appriciated your response. I was beginning to wander if this was an active forum of not.

I have not done anything since my last post, to fix anything associated with the previous CEL occurances. I have not considered purchasing the O2 sensors yet. I thought I would see if the CEL came on again, now that we are headed into the warmer months. I really think that I had some unburnt fuel from burning rich with short coldtrips around town. I'll keep you up to date on the progess of my tests.

I wouldn't mind discussing the noises at start up. Ours has a knocking noise like a stuck lifter. I have seen on this forum where the noise is described as coming from the hydraulic lifters and that once things warm up a bit the noise goes away. This is the case with ours. The forum also as informed me not to be concerned with this start up noise as it is a normal thing for this engine with the amount of mileage mine has.What do you think? Is the noise I hear related more to this Purge Relay" you are describing?

Can you tell me more about this "Purge Relay"? What does it do and how is it associated with the fuel system?

Still love the MPV. I enjoy seeing people's reactionswhen they realize this thinghas 8 seat belts. And love the fact that it fits in our garage. It was the right fit for our needs,we look forward to many future years of use.

Thanks again for your response.
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