Could it be faulty with oxygen sensor or EGR valve? What size socket/wrench for Oxygen sensor? Where is the EGR valve on 98MPV? Is there an unique procedure to reset and rid off this warning? I plan to replace oxygen sensors and clean the EGR vavle. Thanks in advance. Mitvongnam

 

What kind of code do you have set?? There are approx 60 different trouble codes that can be set for any of a variety of things. Leaving the fuel filler cap off will even set a P0455 code for EVAP system gross leak. Many parts stores will retrieve the codes from you van at no charge and will then try to sell you the part they think might fix the problem. Just have them retrieve the code and post back with what you find and you will have a much better chance of fixing the CEL being on.

 

I will try during this weekend to bring the car to Autozone and/or purchase the code scanner tool to do the job.Irecall theCheck Engine Light (CEL) came on at very first time asI completed refillingthe tank with 93 Octane rate gasoline. Soon after the Mazda dealer robbed me $65 to reset the code without letting me know what the code was. I later found out that by disconnecting/connecting the negative cable may remedy the problem. It worked well few times. I had this CEL for over 9 months now. There was neither performance loss on the engine nor unusual behavior of the vehicle at all. But I figure it is about time to do something with the Oxygen sensors and EGR vavle since they are originial items with the vehicle. Shouldn't I??
Regards;

 

Let know what you find out about the code #. Should start with letter P and then 4 numbers ie. P0420 or P1445. Disconnecting the battery cable does not actually fix anything but just resets the engine computer untill the self test for the failed part or system is run and found to be out of specification.
I do not consider it to be a bad idea to replace the front or upstream oxygen sensor at 100,000 miles as this sensor is the primary control for how rich or lean the engine runs and they do tend to wear out and get "lazy" on response time. The downstream or rear O2 sensor is only used by the engine computer to test for catalytic converter efficiency and unless sets a code then would leave it alone.
As for the EGR valvle. 98 MPV does not have one so that solves that issue

 

Babyhue. THANKS. You saved me some money. No EGR valve to worry about. I brought the vehicle to AutoZone forOBD reading. It was dark and late in the evening on Monday. I thought I saw 2 codes, P0410 and P0421. The AutoZone guy cleared it andtold me it was rear Oxygen sensor. He couldn't exactly recall the codes. Any way, the check engine light disappeared for 10 hours. This morningthe CEL came back.Replaceboth front and rearO2?? By the way, I spent some times down underneath the engine (exhaust system).I think it is going to be a challenge to loosen and replace O2(s).
Regards; Mitvongnam

 

What socket size will fit front/rear O2? I tried with vise grip in the past but failed.WHY Vise Grip?? The largest wrench size I have is 19mm. Regards;

 

Well there is not a code listing for either a P0410 or a P0421. Two that might be relating with similar numbers are these.
P0420 is a catalytic converter efficiency below limit. Have yet to see a faulty O2 sensor cause this code to be set but is listed as a possibility in the shop manual.
P0140 is rear O2 sensor no activity which could be a faulty sensor or an exhaust leak between the sensor and engine.
P0141 is rear O2 sensor heater circuit malfunction. This code has always been set in an vehicles that I have seen due to an open circuit O2 heater and O2 replace always corrects.
The wrench size is 22mm or 7/8". Try to use instead of vice grip because the sensorsare often fairly tight and welded in there. Would be well worth the investment to get an box wrench for the job. Looks like the rear O2 sensor will run around $193 and front at $255 for OE which is the best choice for a sensor this important. Never have had much good luck with cheap universal aftermarket sensors.

 

I will try to have the codes recorded. Then determine whether I can handle the task of loosening/replacing front/read O2. Babyhue. Please entertain another question.
What is the official/technical name for the plastic board held by 9-11 screws under the engine? In order to do oil/filter change for 98MPV, this board must be taken off first!! Any idea where I can get one (new/old). I need to replace it. Thanks in advance.

 

It is called an "under cover" in the parts computer. Commonly called an "engine rock shield" as well. OE part number for 4x4 MPV is LB94-56-111A with MSRP of $102.05. 2WD MPV gets different cover with part number LB82-56-111A. and MSRP of $60.55. Both part numbers are still available thru any Mazda dealer. Don't know how much shipping would be but can order thru www.onlinemazdaparts.com for a little savings. $81.64 for 4X4 cover and $48.44 for 2WD.
Possible that you might be able to find a used one in good shape by checking around at some local wrecking yards as well.

 

I had both front and rear oxygen sensors replaced. The Autozone cleared the CEL indicator. After 2 days, the CEL came back.What other possibilities could they be?? Thanks in advance.