If the battery is down, we are just spinning our wheels, trying to test anything. I have seen older vehicles where the mil no longer worked. If that is the case, you cannot check codes. When the mil would not work for whatever reason, I used a scanner that showed live engine data, plugged it into the data-link connector, it worked fine on that vehicle, so I did not think the computer was the problem. You might turn on the key, battery has a full charge, correct. Then check any sensor that uses a ref voltage, If no ref voltage have to start testing at computer, voltage and grounds.
The computer sends voltage to control side of fuel pump relay for initial prime, key on engine off, no rpm needed unless cranking.
Saturday, June 11th, 2016 AT 12:52 PM