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Failing Oxygen Sensor Causing 98 Honda Accord to Stumble

July 24th, 2012 · 3 Comments

Oxygen Sensor Causing Hesitation on Acceleration

I started experiencing some odd behavior with my 98 Honda Accord some time ago which was related to a failing oxygen sensor.  The engine stumbled and bogged down as if it wasn’t getting any fuel when under load approximately one to two minutes after starting the car from a cold start.  Acceleration was difficult and some times I felt it may stall.  The temperature gauge rose to its normal operating temperature athe problem was occuring.

After running poorly for about thirty seconds, normal operation resumed and normal operating temperature was maintained.  If the car was shut off and restarted immediately, the problem did not return.  If it was allowed to cool somewhat, the problem returned.   I also rarely noticed the problem if I allowed the car to warm up while idling.

The CEL and OBD II Diagnostic Codes appear

The Check Engine Light did not come on at first, but after the engine stumbled on several occasions the CEL eventually come on.  After  long periods of driving the Check Engine Light also turned off – So I couldn’t rely on the stumbling to always turn on the CEL or to keep it on permanently.  On one occasion I was going to take the car up to an auto parts store to read the OBDII codes with a diagnostic code scanner, but when the CEL went off, I abandoned my plans until the diagnostic error code returned.

Eventually I was able to get access to a OBDII scanner while the CEL was illuminated. These codes were found:

PO171
System too lean (bank 1)
PO420
Catalyst System Efficiency Below threshold (bank 1)
PO170
Fuel Trim (bank 1)

I began to check a variety of things since these codes seemed to be somewhat generic and I didn’t feel it was the catalytic converter causing the problem.  Although an oxygen sensor could cause driving problems, none of the codes specifically indicated a faulty O2 sensor.  I also made some seemingly incorrect assumptions that a bad Oxygen Sensor would always be detected and that perhaps the effects would be constant or that the ECU would learn and compensate.  I did some research online (I don’t have a repair guide for the 98 Accord, but should get one), basic maintenance and a little engine clean up: checked fluid levels, air filter, PCV valve, cleaned the intake, EGR and fuel injectors – none of which appeared very dirty.  I found a small crack in what I assume was one of vapor lines from for the fuel vapor containment system, I covered this with some latex caulk and did not see the PO420 code return the next time I took the car in to scan the OBDII Codes.

Different OBDII Scan Tool Models Show Results Differently

I used two different models of diagnostic scan tools from two different auto parts stores, the descriptions of the codes were slightly different and in theory I guess could also explain why the P0420 code did not come up the second time.  I also noticed that the some scanners appeared to have some manufacturer specific codes installed while others did not.  These codes may come up as basically unknown in the scanners that did not contain the manufacturers specific data.

Diagnosis and Repair of the Faulty O2 Oxygen Sensor

After doing all of this work, I briefly thought I had seen some improvement; however, I soon realized I was wrong when the problem came back and eventually appeared to get worse.  Discussions with others often brought up other potential causes such as:

  1. MAF sensors – I knew this wasn’t the case, because this car doesn’t have a MAF sensor.
  2. Fuel filter or fuel pump – I highly doubted this was the issue, a problem with these would likely have appeared more constant than the consistently limited manifestation I was seeing.

I figured it had to be some type of sensor or electronic malfunction, but didn’t want to start swapping out parts on a “try it and see” basis.

So, at this time I was debating on whether go scan the codes again or just take the car to a mechanic, I had other things to tend to, my state inspection was due and was getting tired of working on this problem when I didn’t have a clear sense of direction and my previous efforts did not appear to have a definite effect on the problem.

I took it to the auto repair shop that I use when I need the additional expertise or a quick fix.  I explained the symptoms that the car is stumbling or stuttering when under load after driving for a couple of minutes and that it ran normally after about thirty seconds of experiencing the problem.  They hooked it up to their scanner and it directed them to an Oxygen Sensor that needed replacement. At this point I really wished I had taken it to a parts store just to scan it one more time to see if that code would show up for me now and it had just taken a while for the failing sensor to be detected properly.   I asked the mechanic about it, he said their scanners cost thousands of dollars and do a much better job than the consumer models.  I let them replace it and the job was done.  It would have been nice to find and fix the failing O2 Sensor my self, the O2 sensor doesn’t appear to be very difficult to replace and Amazon even has a replacement Oxygen Sensor.  A specialized Oxygen Sensor Socket exists for cases where a wrench cannot be used to remove and install an oxygen sensor, since these sensors have a connection wire on the top.  I’m glad my car trouble is solved now, with a little help from others.

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