CEL & Fuel Cap

[YuCrew]

The CEL light on my '99 ML430 with 98,000 recently came on and the OBD generated a P0156 code (driver's side O2 sensor, after the cat I believe). Refueled with 93 octane, put the cap on and then noticed the CEL was out. 20 miles later it was on again. Refueled again a few days later, made sure the cap was tight (also did visual inspection of seal and could see no deterioration) and when I started the engine, the light was out again. That was 100+ miles ago and the light is still out. Anyone care to guess about whether I'm dealing with an O2 sensor ready to fail or combination of fuel cap and octane? Thanks.

[drbenz05]

more than likely its the 02 sensor . have ran into sereral on the ml430

[Ron in SC]

I had the P0156 code a few months ago, no reoccurence so far.

See: http://www.peachparts.com/shopforum/showthread.php?t=119639&highlight=sensor

[YuCrew]

Ron: I was not able to determine whether you finally decided to replace the o2 sensor after the cat or ignore it. I read your prior post on this subject and while I found the information really interesting, wasn't able to completely determine if you replaced it or the light simply vent out by itself.

Thanks.

[Ron in SC]

Jim,

Did not replace the O2 sensor. The light when out and has not come back on. If the light had come back on I probably would not have replaced the sensor until I got tired of looking at the CEL. I don't think the failure of the after CAT sensor affects performance.