Can't read ECU code

I can't get a code reader to connect to the ECM plug under the dash. I have been to 4 different auto parts stores. The code readers keep saying no connection.

I checked the ECM fuse under the hood in the fuse box which is located right over the battery. I replaced the fuse with another one to make sure. Still nothing.

Am I missing a fuse or something else? I didnt' see anything related to the ECM in the fuse box located at the passenger side door. . There is a PCM fuse but I think that has more to do with the transmission.

By the way, I just replaced the Fuel Pressure Regulator. The van runs much better but I think there is still something going on with a sensor. The Service Engine Light is still on. I've tried resettign the ECM by disconnecting the battery for a few minutes.

I'd like to check the codes but can't do to problem just described.

Year of vehicle?

check the tps sensor and clean the iac right above the tps .autozone scanned mine try them

I have taken my van to 4 different auto parts stores. Each handheld machine will not recognize it is connected to the ECU plug under the dash.

I have checked the fuses. Any ideas?

Sorry. 98 Chevy Venture.