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RGibson -> Coolant Temp Sensor - Cold Start Problem (3/12/2008 12:08:06 PM)
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I have a 1997 Chev Express big block. Here is the problem I am having. In cold weather the engine will not start. I plugged into the diagnostic port and found that the coolant temp sensor was reading 98 degrees C. So when I saw this I thought I have the problem solved, a faulty coolant temp sensor (also knowing that this sensor would tell the ecu to fire the cold start injection). Once I got to it, I put a new sensor in and thought all was good. I check my scanning tool and it said the coolant was STILL at 98 degrees C. I knew then that something more was wrong. So I looked at the signal voltage. Any other temp sensor I disconnect (inlet air temp for example) will go to 4.98 volts or -41C. When the coolant temp sensor is disconnected it stays at 2.00 volts (98 degrees C).
I thought maybe the problem might be in the connector, so to verify the connector was bad I took a piece of wire and jumpered the sockets. When I did this, it went to 0 volts (appx 141C if I recall correctly) as I would expect but removing the jumper it went back to 2.0 volts. Again for comparison sake I tested other temp sensor inputs and found that when I shorted them it went to 0 volts and when I removed the short it went to 4.98 volts. All as I would have expected.
So still thinking it was the connector (perhaps a slight internal short), I replaced the connector and guess what. Still the same readings. The one last thing I did check was resistance between the terminals of the connector which I see as being appx 690 ohms. When I check other temp connectors I find them to be open (infinate resistance).
So at this point I am asking for help and any ideas that you may have. For some reason that circuit will not read below 90 C and given that it is way colder than that there is no way the ECU will know it is cold and I will continue to have the cold start problems. Any suggestions
Thanks
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