It is possible that if the PCM had any loss of communications codes, you would have saw them with your reader. That is about all it's capable of interrogating. The check gauges light, is just that, it's alerting you to the temp gauge light. The fact that you say it is below the zero stop tells me that it has spun completely around. Here are the two causes for check gauges light.
The instrument panel cluster (IPC) illuminates the CHECK GAUGE. Indicator based on a class 2 message from the body control module (BCM). The BCM will command the CHECK GAUGE. Indicator ON when the following occurs:
" The fuel level falls to or below 5%
" The engine coolant temperature is hot and exceeds 107 C (225 F)
The CHECK GAUGE. Indicator displays in the IPC whenever any of the above listed conditions are present. If the CHECK GAUGE. Indicator illuminates when the fuel gauge and coolant temperature are operating normally, check for the proper operation of the BCM.
I took a look at the diagnostic chart for temp gauge inaccurate or inoperative, it just refers to the gauge sweep test I had mentioned earlier. That would be the next step in the diagnostic process. Here is the chart.
Engine Coolant Temperature Gauge Inaccurate or Inoperative
Schematic Reference: Instrument Cluster Schematics
Did you perform the Diagnostic System Check - Vehicle?
Go to Step 2
Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
Install a scan tool.
Turn the ignition ON, with the engine OFF.
With the scan tool, perform the Coolant Gauge Sweep Test.
Does the engine coolant temperature gauge move up and down when commanded?
Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems
Go to Step 3
Replace the instrument panel cluster (IPC). Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.
Did you complete the replacement?
Go to Step 4
Operate the system in order to verify the repair.
Did you correct the condition?
Go to Step 2
Wednesday, April 7th, 2010 AT 10:25 AM