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I have a 89 Civic 1.5 hatchback that keeps setting a (6) code on the ECM. I have replaced both temp sending units and the thermostat. The motor is not hot, I’ve checked it with a laser thermometer. It will set the code within a few seconds of starting the engine. If I let the engine come up to operating temp I can watch the thermostat cycle with the laser. After the motor is warmed up, I can kill the engine and reset the ECM and it will run all day without the check engine light or the 6 code coming on. Let it cool down, start it up and bingo the check engine light and 6 code come back. This is making me nuts.
Thanks for your help