[rushing1]

I have the same random P0420 code on my 1999 Odyssey.

I had the Honda EGR TSB performed at 92,000 miles. Even though it was past the 80,000 mile warranty Honda paid 1/2 the repair cost.

The check-engine light came on while I was on vacation with 99,600 miles on the van. I drove 100 miles 1 way to a Honda dealer to have the code checked in case it was set because of the transmission.

The dealer reported the code was P0420 and offered a catalytic converter replacement for $850. I asked if I could safely drive home (1000 miles) to have the repair performed. The dealer said no damage would occur to the van if the performance and mileage remained unchanged. The van was running perfectly, so I decided to return home before having any work done.

One week later, the light went back out. Since then the P0420 code is set occasionally, but within 2-3 tanks of gas it goes back out so I have never replaced the catalytic converter. The light has always been out at emissions inspection time. I now have 157,600 miles on my van.

I have never been able to correlate a gas station / driving pattern that causes the light to come on or go back off. I track the mileage on my van every tankful, and there has been no change. On a yearly basis my van averages 20.6 mpg, +- .3 for combined city (18.5) / highway (23.8) driving. I have gotten as low as 13 mpg in town, and just this Thanksgiving as high as 28 mpg on the highway.

I realize there is no technical data in this post, just a note that another owner has the same random P0420 code.

 

[rushing1]

Update to 1/23/2007 post

This is an update on my 1999 Odyssey with the PO420 code.

I now have 203600 miles on my 1999 EX and have been seeing the PO420 code since 99,500 miles in 2003.

At first the code would only be on for 1-2 weeks at a time, then off for several months.

By my 2006 inspection, the light was on most of the time, but I was able to pull the fuse to reset the code and pass inspection. The light came back on within 500 miles.

For the 2007 inspection, I was able to reset the code, drive 50 miles in D3 to keep rpm's 2500-3000 and was able to pass inspection. The light came on 2 miles after the inspection. On looking at the inspection form, the rear O2 sensor was 'Not Ready', but I could pass inspection with 1 sensor 'Not Ready'.

For 2008, I reset the code, but the light would come on before the rest of the system was out of 'Not Ready'.

I decided 203000 miles was enough on one Catalytic Converter and ordered a new one from Majestic Honda (see Honda Automotive Parts on Link page), along with the two gaskets. Total $650. including shipping.

A local suspension/exhaust repair shop installed the cat for $70. It took them 20 minutes. Since I do not have good jack stands, or power tools to break the bolts loose, I felt it was $70. well spent.

The PO420 code went off immediately and my van has now passed inspection. I will update this post if the code comes back on.

Notes:

Original O2 sensors. I tried cleaning the rear O2 sensor with electrical contact cleaner, but it did not make a difference.

Original Transmission: Frequent (10-18K drain/fill of fluid)

Always use 87 Octane gas, Texas used to use MTBE, now 10% ethanol

Use Mobil 1 Synthetic 5w-30 through 150,000 miles, then Pennzoil Platinum Synthetic 5w-20, and Motorcraft Semi-Synthetic 5w-20.
Changed between 6000 - 8000 miles.

Van runs like new, 25 mpg @ 70-75 mph on recent trip (before cat replacement)