98 Check Engine Problem

DOHC model

My check engine light has been on for a few months. To pass inspection where I live, my check engine light has to be off (or at least not report anything emissions related). I had it scanned and it came up with "Insufficient flow in the EGR System". I was told that it was probably the O2 sensors and not the EGR valve. I had all 4 changed. The light stayed off, but kicked back on after about 60 miles.

I brought it in today to have it scanned and it came up with the same "Insufficient flow in EGR system" and 2 codes for a "Malfunction in the heater circuit for O2 Sensor 1 in bank 1" and "Malfunction in the heater circuit for O2 Sensor 1 in bank 2". The car has 108K miles on it, and the O2 sensors did help my milage out a lot. (approx 70 miles per tank of gas more!)

The guy at Autozone told me to check the fuse for the O2 sensors. I did, and it is good. Should I try pulling the battery and resetting the computer again? Anyone have any words of wisdom?

I have read that it is probably not the EGR valve, but maybe the sensor? Also, I need to know where these parts would be located on a 98 with DOHC.

Your problem is probably a DFPE switch. This is a small vacum switch for the EGR valve and is a known common problem on this car. Although a numerical code would be better to diagnose with, because I don't know if the info I just gave you applies to DOHC cars or not.

The codes that it gave me were

P0401 (insufficient flow in EGR system)

P0135 (malfunction in heater circuit for O2 sensor 1 in bank 1)
P0155 (malfunction in heater circuit for O2 sensor 1 in bank 2)

Should I be worried about the last 2 codes since I just had the O2 sensors changed 4 days ago?

Without seeing some real-time data on the o2 voltages it's really hard to tell if they are working. Normally the fuel computer runs full rich on start-up and I guess it may be possible the EGR problem may be causing soft codes on the O2 sensors. I can't imagine they are shot this soon. Maybe a fuel trim malfunction is causing the codes to appear but it's a little deep for me to know. If it were me I would concentrate on the EGR problem, correct it and clear the codes, then see if the light comes back on after 2 or 3 trips from a cold start.

I replaced the EGR vacuum switch yesterday. Reset the computer, and drove my car to work today. On the drive home the check engine light kicked back on. I stopped at Advanced Autoparts and had them scan my codes. The same 3 codes showed back up.

P0135
P0155
P0401

They suggested that I change the EGR valve itself.