Q: Car won't start key turns and lights dim when it cranks. I just don't hear a buzzing sound from the fuel pump when turn key to on

Code U1100 signifies a communications error which is either a module fault or a deficiency in the wiring harness between communicating modules. There’s a possibility that a dying battery is a cause of such a code (and a cause of your no start condition, as well) and so the very first thing to do is be sure you have a fully, 100% charged battery that passes a load test. Then, confirm that the engine immobilizer system (security system) is not activated thus preventing the car from starting. If the immobilizer system is on, you may see a security warning light. To temporarily override the immobilizer system, see these instructions.

If the battery tests good after an actual load test, attempt to start the car. If there is no starter motor operation at all, that is if there is no starter operation with the key held in the "start" position, the procedure is to test for power and voltage drops to the starter motor/solenoid. If there is no power, or a large voltage drop is measured, then the electrical circuit supplying the motor has a fault. That circuit begins at the battery and includes grounds, wiring (some of which is very heavy cabling), fuses, relays, the ignition switch, neutral start switch, and terminations. Basically, with a fully charged battery, and with the key held in the "start" position, the starter is either getting power or it isn’t. With the key in the "start" position, IF the starter motor is getting power but the starter does not work, then the starter is condemned and replaced. On the other hand, if the starter motor is NOT getting power, then the circuit is diagnosed and that diagnostic, in your circumstance, may have a tie-in to the U1100 code. That remains to be seen, of course.

If the above protocol does not identify the issue for you, please simply request a no start diagnostic and the responding certified mechanic will get this taken care of for you promptly. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.