Volkswagen: VW passat, engine coolant temperature, oxygen sensor

Question
QUESTION: The MIL light came on my '02 passat glx automatic after a bad snow storm during which the snow plows plowed the street and piled the snow up against the rear of the car presumably against the tailpipe.  The light came on and the car sputtered and would not start.  Once I cleared the snow, the car started and idled quite roughly for a while but eventually smoothed out and ran okay.  The MIL light went off and all seemed okay.  Recently, however, the light is back on and has not gone off.  Also, now that the cold is upon us, I recently noticed that there is no heat.  After about two hours, you can begin to feel "warm" air come through the vents but it never gets hot like it used to.  The A/C works fine and there is enough coolant/antifreeze.  Could these be related or is it likely that the MIL refers to an emissions problem, i.e. an oxygen sensor, and the lack of heat due to a faulty thermostat or water pump?

ANSWER: John,
  I would say the MIL light and the heater are not related.  I would get an OBD scan to determine the reason for the MIL.   The computer may just need to be reset properly, which can be part of the scan.
 The heater core may have a clog, this is known to happen on these models when the wrong antifreeze is used. Have the system flushed and use only VW approved coolant.
- Rick

---------- FOLLOW-UP ----------

QUESTION: Rick,

I had my OBD scan and the following codes came up:
P0118 (Engine Coolant Temperature Circuit High Input), P0161 (Sensor Heater Circuit Malfunction Bank 2 Sensor 2), P0056 (HO2S Heater Control Circuit Bank 2 Sensor 2),
P0491 (Secondary Air Injection System, Bank 1 Insufficient Flow)
P0492 (Secondary Air Injection System, Bank 2 Insufficient Flow).

I realize that some of these codes may be related to the oxygen sensor failure but I have two questions.

First, can the P0118 (Engine Coolant Temperature - Circuit High Input) be the result of a clog or having used an inappropriate mix of antifreeze?  Is it possible that the antifreeze mix is too cold or even freezing when the ambient temperature is below freezing?  I plan to take a look at the thermostat and drain/flush the system but figured while I was doing that I would address whatever other problem may exist.  

Second, can the codes for the faulty oxygen sensor be related to needing a new catalytic converter?

The car is a 2002 Passat GLX with about 55K miles on it.  It has no loss of power, no foul smell (sulfur) and really no symptoms other than the lack of heat.

Answer
John,
 I think the P0118 is an easy fix.  Just check the sensor connections or replace it.

The P0161 is likely a bad O2 sensor or connection.  Another possibility is the O2 heater relay (these are heated O2 sensors for better performance).

I am not familiar with the P0491/492, but here is a link to a similar Audi situation:

http://answers.yahoo.com/question/index?qid=20080618180801AADPKSb

Rick