Hey all. Quick question:

Yesterday, I changed the water pump on my 1997 C280 (88,000 miles). Straightforward job, no real drama.

Today I did a few local test drives (total of 50 miles or so). The car started, re-started, and ran well. Then, all of a sudden, the idle went rough and the CEL (check engine light) came on. I *assume* it's related to my recent work.

Notes:
- I checked the tiny vacuum hoses and electrical connectors in the area of the water pump. All seemed intact.
- I did not bleed the system of air because I could not find a bleeder valve, so I *assumed* that is not necessary. Can an air pocket trigger the CEL?

Any relationship between a new water pump and the CEL?

Your advice is much appreciated.

Air pocket will not trigger the CEL, just blast your defrost for a while and then recheck the coolant level, that's a quick way help eliminate air pockets.

Did you install a new thermostat? I imagine a stuck open/closed thermostat would set the light. But the most common fault with that engine is the original wire harness. If you disrupted the old crusty harness, you may have broken or cracked some of the wires. That is a common cause of check engine lights that immediatly follow engine repairs -at least on the 104 engine.

Thanks for the input. I will look into it. Yes, there were a few bad connectors. I cleaned them and put shrink tubing over them for protection. I will reinspect them.

By the way, any off-the-shelf anitfreeze recommendations that will work with these cars? At 90K miles, I was ASTOUNDED how clean the inside of the old water pump was. NOT ONE bit of old accumulation -- just shiny aluminum. Wow.

Any other ideas, I am all ears.

Thanks!

It would help if you could retrieve the stored trouble code (s ).

__________________
2007 C 230 Sport.

Capturing codes is beyond my ability, I am afraid. My tool box is pre-OBDII.

I reset the computer and will take it for another drive to see what happens. It previously started and ran beautifully. Turned it off. Seems something happened during the heat soak. Restart was a little rough. It got worse. CEL light then came on.

Isn't there a way to get codes through the AC control? I will have to search for that.

Capturing codes is beyond my ability. My tool box is pre-OBDII.

I reset the computer and will take it for another drive to see what happens. It previously started and ran beautifully. Turned it off. Seems something happened during the heat soak. Restart was a little rough. It got worse. CEL light then came on.

Isn't there a way to get codes through the AC control? I will have to search for that.

Time to upgrade your toolbox.
http://www.iequus.com/item.asp?cid=10&pid=3100
It works on all 1996 + vehicles, not just M-B's.

__________________
2007 C 230 Sport.