I've done a search on this problem and never really found a definitive answer. The check engine light came on the other day (2007 - 4wd). I have a code reader so I checked the codes. I got a P2243 - the O2 Sensor. Not a huge deal, kind of a pain from what I can tell, but not a huge problem, I'll get to it this weekend. Today the check engine light and the VTM-4 light came on. Checked the codes again, got P2243 again, and P0134 - also a problem with the O2 sensor. Why would the O2 sensor cause the VTM-4 light to go on? From what I've read so far, the VTM-4 light seems kind of pointless and goes off at random times for random reasons. Is there something else going on I should be aware of? Or would replacing the O2 sensor just fix the problem?