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OK everyone, this one has me completely stumped....
2003 9-5 Areo, Automatic
Symptom:
After driving and car is warmed up, dashboard temp guage goes to "zero", sometimes check engine light comes on.
This has been happening for a bit over a year, but goes away when the outside temp at cold start is above 55-degrees(F) so I do not see it through the spring/summer/fall.
I have spent the last couple of months really looking at what is going on and observing, this is what I know:
1:This only appears to happen when the outdoor temp at cold start is below 55 degrees (this happens on my drive to work in the morning when it's cold, but not in the afternoon on my way home for example)
2:This happens sometime between 15.0 and 16.0 minutes after starting the car, very predictable
3: I have an OBD-II reader. If I plug it in and read the live data after the temp on the dash drops, the temp from the OBD-II port has not changed. (when this happens, the temp is between 152 and 156 degree) If I monitor the temp both before and after, the OBD-II temp does not change.
4: Saab dealer replaced the temp sensor on the cyl head about a year ago when this started. Unfortunately, this was at the end of the spring and I didn't see this again until late Fall when it started getting cold again.
5: If I restart the car after the temp goes to zero, the temp guage is fine. It will not do this again until I go from a cold start again.
6: If before the temp goes to zero, but after the car has started to warm up, I stop the car and restart, this will not happen.This can be done in as little as 5 minutes after the initial start.
7: happens at both highway and start-stop speeds
8: The OBD-II diagnostic code when the check engine light comes on is "temp out of range"
9: If I start the car and let it run for a few minutes and unplug and quickly replug the temp sensor on the cyl head, I get the same behavior. (Temp guage on dash goes to zero, OBD-II temp stays where it was) If I unplug it for too long, the check engine light comes on.
I had a theory that this was an intermittent or a nearly-broken wire (thus doing the test #9 above) but I'm not convinced since it has NEVER happened except when the temp is below 55 and I go from a cold start.
I have been thinking that there may be some kind of relay in the ciruit between the temp sensor and the dash guage that switches when it thinks the car has gotten to operating temp on a cold start. If there is a failure in that relay that gives a short "open circuit" during the switch, this would generate this kind of issue. Does anyone have a wiring diagram for this car that could verify this?
posted by 76.103....
, Fri, 27 Mar 2009 03:07:31
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