Rep Power: 0

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.

 
Rep Power: 0

Just to be sure, if you have on available, substitute a known good ECU. I know it sounds like something you've already heard from a manual or something. It is one true way to use process of elimination to figure out your problem. They do go bad,sometimes.
peace,b

 
Rep Power: 228

In addition to a faulty ECU, you should also consider a problem with the TW sensor circuit:

 
Rep Power: 0

you can also get on google and there is a way to reset your ecu after you fix the error so the code wont keep coming up