[Tobyj96]

'89 Cadillac DeVille, just past 100K this month.

Out for a short drive last night. The Check Engine light flashed for a brief moment. Quick enough that had I not been looking at the dash at that moment, I wouldn't have seen the light even come on. On, Off in less than a snap of the finger.

Get to where I'm going, pull the OBD codes and it's Code 13 and 48; O2 Sensor and EGR, respectively. Clear codes, and no repeat of the incident.

Question which is it: Actual 02/EGR fault, the Catalytic Converter temporally acting up a little, or just a random gremlin in the diagnostics?

 

[MoistCabbage]

Converter efficiency isn't monitored on your car. EGR and O2 sensors are totally separate systems. If you got those codes, those are the parts/systems that have issues.

Only strange thing is, the check engine light should have stayed on for several ignition cycles, even if the codes went immediately to history.

I would clear the codes, drive it for a couple of days, and pull the codes again (regardless of weather or not the light illuminates again). If the codes come back, there's an intermittent problem.

 

[Tobyj96]

Converter efficiency isn't monitored on your car. EGR and O2 sensors are totally separate systems. If you got those codes, those are the parts/systems that have issues.

Only strange thing is, the check engine light should have stayed on for several ignition cycles, even if the codes went immediately to history.

I would clear the codes, drive it for a couple of days, and pull the codes again (regardless of weather or not the light illuminates again). If the codes come back, there's an intermittent problem.

I was thinking cat cause of an old Jimmy we had that through an O2 fault, and found that the cat was restricted cause it to read fault.

IRC--been ages sense I've dealt with an O2 sensor going batty--and O2 sensor doesn't shutdown the engine, just makes it run rich, bad fuel mileage, and eventually run really crappy--non of which is currently going on.

 

[mc_marto]

The E.4.8 code for the EGR system is set with the help of the oxygen sensor. I would think you'd have to clean all your EGR passages, and make sure there are no problems with the EGR vacuum tubing (from throttle body to EGR solenoid and from EGR solenoid to EGR valve). The E.4.8 should have kept the CEL illuminated for the whole ignition cycle. And if there is still fault in the EGR it might take a couple of hundred miles for the code to come back (depending on the majority of your driving - the system checks for faults when under steady cruise at highway speeds).

If you find and fix the EGR problem and the o2 sensor code comes back, you can try something before replacing it. It's generally not good to clean them with any type of solvents, but you can try burning off the deposits with a torch. That's also a wonderful time to conduct testing on it (while using the torch on it). You would need a DVOM set to the 2000 mV scale. If you need more info about the test, let me know.