Hi all,

I have a 98 Rodeo (3.2 V6) at 142Kmiles. For the last 3-6 months, I had the Check Engine come on and off frequently. When I read the code, it was for an O2 sensor.

Today, I took the truck for an emission test (Irvine, California). Although the reading was OK at 25 mph, it wasn't at 15 mph.

Here are the values for the guru:

HC (PPM)
15 mph - Max: 46, Measured: 6
25 mph - Max: 29, Measured: 6

CO (%)
15 mph - Max: 0.58, Measured: 0.09
25 mph - Max: 0.72, Measured: 0.11

NO (PPM)
15 mph - Max: 488, Measured: 565
25 mph - Max: 741, Measured: 561

Seems like I have a Low HC, Low CO, High Nox situation at 15 mph. I remember reading somewhere that this profile is consistent with a stuck EGR valve. Is that the case? If so, I'll probably get the EGR replaced... Where should I buy one? Lastly, how much a job like this should cost (so that I'll have a reference point when I call around)?

If this doesn't seem to be an EGR issue, what else could it be?

Thanks very much in advance for any suggestions. Other than this, the truck runs great!

EDIT: I stopped by the Jiffy Lube around the corner, and they read the codes. Two showed up... Here they are:

1. P0401 - EGR flow insufficient

2. P0430 - Catalyst efficiency below threshold (Bank 2)

I hope these would be helpful to figure out what needs to be changed, cleaned, etc.

Thanks again for your time and help!

You certainly do have an EGR problem that is related to your NOX emissions. That is the only function of the EGR system is to reduce NOX. 'EGR Flow insufficient' may or may not be a defective EGR valve. You should start by removing the EGR valve and checking that the tube is clear and then cleaning the valve itself. I don't know if the valve on your year is vacuum or electronic but if it's vacuum you need to see if it opens under vacuum and hold that vacuum.

The other code could indicate a bad catalytic converter or a bad post-cat O2 sensor. You would need to have someone determine which.