OBD-1 codes: 335, 172, 173, 336

[jdt70]

I thought I would run this by you guys before I started buying parts. I am having a problem with my ’94 Explorer. The check engine light comes on and engine bogs down intermittently after driving several hundred miles. This occurred again recently when I drove it from NC to MI. I was able to pull the OBD 1 codes and this is what I got:

Key on Engine Off (KOEO) test:
Current codes – 335 EGR sensor circuit voltage higher or lower than expected.

Stored Codes (cont. memory) – 172 Heated oxygen sensor fault / lean bank 1 / right side
173 Heated oxygen sensor fault / rich bank 1 / right side

Key on Engine Running (KOER) test:
336 EGR circuit higher than expected / exhaust pressure high

All other test normal

I am guessing that the exhaust pressure high (and maybe the other codes) are due to a plugged catalytic converter. What do you think? Should I change or punch out the cat? Could the O2 sensors be related to the back pressure? If you get a chance let me know. If the O2 sensors are telling the EEC that I am rich or lean that would explain the bog down. Thanks for any recommendations.

 

[MrShorty]

Double post, see response in stock 1st gen forum.

 

[FixingDaily]

Mr. Shorty,

I am new to this forum and you have been helping out on my self test issue. I was searching for information on the code 335. Could you help me out by guiding me to the answered thread.

Thank you again.

John

 

[MrShorty]

Probably not, but if you put code 335 or other EGR related search string into this site's search engine, you'll find plenty of discussion.

Because KOEO codes are set with the engine off, they almost have to be electrical -- in this case the PFE/DPFE sensor circuit. A lot of the time, the PFE/DPFE itself is the culprit.

 

[yragsapo]

I recently had the 335 code on my '94 Explorer. I change the EGR pressure sensor (simple repair) and the check engine light went away, the engine stopped pinging under load and I could feel power return to the engine. As I just changed the sensor yesterday, I will have to see if the MPG goes back up.