If the check engine light was on, there was a diagnostic fault code in the engine computer. That got erased when the battery was disconnected. The goal is to not disconnect the battery or let it run drained, otherwise that valuable information and all learned data will be lost. The fault codes indicate the circuit or system that needs further diagnosis. Erasing the codes does not make the problem go away.
There is a bigger problem when driving with the check engine light on. First, that means there is a fault code set. There is always a long list of conditions that must be met for a fault code to set, and one of those is that certain other codes cannot already be set. The computer compares various sensor readings and operating characteristics to determine when something is wrong. For example, it knows that when the engine has been off for more than six hours, the intake air temperature sensor, coolant temperature sensor, and battery temperature sensor had better be reading the same temperature. If a fault code is set for one of them, the computer knows it cannot be trusted as a reference, so it suspends any self-tests that use that defective circuit for comparison. If a problem develops in the other circuit, it will not be detected because that test is not taking place. It is not until the first problem is repaired that the suspended tests resume. That can cause a lot of frustration among car owners and their mechanics. The mechanic only knows about the stored fault code and has to go by that when preparing a repair estimate. Once that is solved and you leave with the car, the suspended test resumes, the problem is detected, the check engine light turns right back on, and you incorrectly assume the first problem was not diagnosed correctly or was not repaired correctly. The mechanic has to start all over.
The other problem with ignoring the check engine light is a lot of problems are very minor with inexpensive solutions, but they can turn into expensive repairs if they are ignored. How will you know if one of those has developed if you are already driving around with the warning light on? The simple misfire you mentioned will send unburned air and fuel into the exhaust system where it will burn in the catalytic converter and overheat it. Most commonly the cause is a worn spark plug or bad spark plug wire, but the catalyst will melt in the catalytic converter and become plugged. That is a real expensive repair that can easily be avoided.
What has confused the issue is your description of "does not start". The common symptom after disconnecting the battery is the engine cranks just fine, but the idle speed is too low for it to run. That is where holding the accelerator pedal down a little will get the engine running.
Now you are describing a no-crank condition which is quite different. The anti-theft system is not involved in that. One common cause is a defective neutral safety switch/range sensor, but it sounds like you have an even more common problem. It is real common for fuses to blow when reconnecting the battery or when connecting jumper cables, from the current surge of the memory circuits in multiple computers charging up. The clue is the dead radio. I would start by checking them in the under-hood fuse box, and inside the car.
Wednesday, January 10th, 2018 AT 6:59 PM
