240 240 123 Code, bad signal from ECT

Just started getting an issue the other day. All the suddenly the other day, after about ten minutes of driving, the engine light came on for the first time since I've owned the car. Checked the computer, it said 1-2-3, nothing on port 6. Cleared it, drove it home, nothing came on, thought I was set.

Came on again yesterday after a minute, now it won't go away. Shows 1-2-3 on port 2, nothing on 6. I have checked the ohms from the sensor pins to sensor body after car cooled off for a couple hours, it started at 1.2k ohms and is slowly going up, currently at 1.9k, which seems correct according to the charts, that would mean about 80 degrees. So I don't think it's the sensor.

Sensor wiring, etc looks good. Pulled back the rubber boot, not ripped up or destroyed, contacts totally clean with no corrosion. Grounds not the issue.

All I can think of is the pins were a little bit dirty and hopefully reseating them will solve this.

Any other possibilities? Car runs just fine. It MIGHT be consuming a bit of extra gas, but since it only just started I really don't know.

Use some electrical contact cleaner on the pins and connector. Also check the grounding strap from the valve cover to the firewall. Make sure it's clean and tight. If it's corroded that can cause false readings. Also check the fuel ecu number and make sure it's not a 561. If it is one with a pink label. I'd shop for a 951 to replace it with.

Thanks for the tips, very useful. Plugged everything back in, started it up, shook those pesky ground wires by the intake runners (the multi wire to one wire solder joint), no light came on. Hope that was all it needed. I'll report back if it keeps popping up.

Edit: two days since cleaning. No issues since cleaning. I'll update if it goes on again, but I guess even if it looks clean, it's not.