Hi, I am new to the forum, and this is my first post. I have a 2004 ztw with a 2.3 that I had in the shop. The tech found a p2557 code and, replaced the smog pump fuse. The cel went away then returned the next day. I checked the fuse, relay, and solenoid... all good. How can I check voltage at the pump harness if the system may or may not be engaged. I don't want to change the pump for the heck of it, its pretty pricey. Thanks.