How do I troubleshoot an error code #9 ?? I have 95 LS/VTEC with an OBD1 ECU, distributor, etc. using a Conversion Harness adapter. I am using a P28 chipped ECU which is looking for the Knock Sensor signal. This initially triggered a CEL code #23 which corresponds to Knock Sensor, but the car idled very erratically. In checking it out a friend found out that the plugs were messed up - so we replaced them and the engine sounded much better and revved out pretty nicely. But now the CEL #9. What could cause this ?? Thanks for any help.