5EK 3406E electrical help!!

Were the parameters in the replacement ECM configured the same as the original? Either have to save the original configuration file with ET, then write it to the new ECM, or alternatively you can write them down and manually input them with ET.

 

Check all battery connections and all grounds. Inspect all harnesses.
Engine code 21 on 3406e

 

Why are you paying the shop when they didn't fix your problem?

That code means the ECM isn't getting the 5 volts it needs on the reference circuit for your sensors. One of the sensors is going bad or you have a problem in the wiring somewhere. You can replace the entire engine harness yourself in just an hour or two for only a couple hundred dollars if you don't know how to track down the wiring issues.

If that doesn't fix it then you have to figure out which sensor is the problem. None of them are expensive or hard to replace. This is another job you can do yourself without getting stolen from by the hack of a shop you went to.

Next I recommend removing all your grounds then clean them until they're shining on the connectors as well as where they mount. Check the wires very carefully too. Sometimes they look good to the eye but they're corroded up inside the coating if they are really gray.