2006 Nissan Frontier with code U1000

Question

Already checked harness ground and ECM relay. Still won't start showing code U1000

Answer 1

You have to clean the grounds also 

1. Clean/re-tighten ECM ground connections.

2. Clean/re-tighten negative battery cable body connection and battery post connection.

3. If needed, clean and ensure good contact between the steering member assembly

and the left side instrument stay assembly.

Here is the Nissan Service bulletin

https://www.autocodes.com/uploads/nissan/NTB06-009a.pdf