1992 940 Check Engine Light (Kinda)

[rrussell]

My check engine light dimly lights up after about 5 minutes of running and stays dimly lit most the time. When I say dimly, it is almost not even visible during the day. The code it is throwing is 123 (signal to ECT), sometimes the check engine light will come on completely and bright (plainly visible during the day) and a 232 (O2 sensor) code is thrown in addition to the 123.

I'm puzzled why the check engine light is just barely coming on. Anyone have any ideas why it would behave this way? I'm thinking it just might be a electrical ground issue? I got the following list of spots to check, are there any others? Anything else I could do to diagnose this?


-Battery chassis near the battery: frequently corroded
-Engine main ground under the p/s pump (typically OK because of oil coating)
-Engine ground straps from the distributor and intake manifold to the firewall: crimps can loosen or corrode
-Right auxiliary chassis ground (behind right headlamp): frequently corroded
-Left auxiliary chassis ground (behind left headlamp): frequently corroded
-Inside left A-pillar: underneath the trim panel by the bottom front left door hinge; damp carpets can corrode this
-Inside right A-pillar: just beneath the engine computer by the right front door pillar; this is important since so many functions ground here and humidity/salt can affect it from the carpets.
-Left and right taillight grounds; often corroded and a cause of malfunctioning rear bulbs
-On the right console between the seats: usually not a corrosion area but the strap to the transmission can corrode
-Courtesy lamp ground above the left B-pillar; usually not a problem
-Fuel pump and sensor ground next to sending unit on fuel tank: frequently corroded
-SRS ground beneath the driver's seat next to the crash sensor. It goes without saying that if you are going to touch this, you need to disconnect the battery negative and wait some time for any charge to dissipate from the crash sensor.