How to Troubleshoot a Car with Full Accessory Power but Won’t Start

The reason the car won’t start is because the full accessory power is active.

Full Accessory Power Active Car Wont Start

When a car won’t start, it can be very frustrating. If your car has full accessory power but won’t start, it could be caused by more than one issue. Some common causes include a dead battery, faulty starter motor, or problems with the fuel system. It is essential to first have a qualified mechanic check your car before attempting to diagnose and fix the problem. The mechanic is experienced in identifying and repairing any issues related to the starting of your car. They can also perform necessary tests to determine why the car wont turn over. Once they have determined the cause of the problem, they can quickly get you back on the road again!


A dead battery is one of the most common causes when a car won’t start. It can be due to a faulty alternator, loose connection or just age. To check if the battery is the culprit, it’s important to test its voltage with a multimeter. If it registers below 12 volts, then it’s likely the battery is dead and needs to be replaced.

It is also possible that the battery cables are loose or corroded, so make sure these are checked as well. If they are in poor condition, it may be necessary to replace them before attempting to start the car again.


Another potential cause of a car not starting is a blown fuse. The fuse box in most vehicles will have a diagram that shows which fuse corresponds to which component. Carefully inspect each one for any signs of damage such as melted plastic or discoloration from overheating. If there is no obvious sign of damage, then use a multimeter to test for continuity between each end of the fuse.

If any of the fuses are found to be blown, replace them with new ones that match their amperage rating and try starting the car again. If all of the fuses are found to be in good condition, then move on to checking other components such as relays and sensors that may be causing an issue.

Fuel System

A blocked fuel system can also prevent your car from starting up properly. This can be caused by clogged fuel filters or bad fuel injectors that are not spraying fuel properly into the engine cylinders. To test this, check for any leaks in the lines leading from your gas tank and inspect your fuel filter for any signs of clogging or dirt buildup. It’s also important to make sure your gas tank has enough fuel in it for your engine to run properly – if it doesn’t have enough pressure then it won’t start up properly either.

If all these components appear to be working correctly, you should then take your vehicle into a mechanic and have them run diagnostic tests on your vehicle’s electronic control unit (ECU). This will allow them to identify any faults with your fuel system that may be preventing your vehicle from starting up correctly.

Ignition System

Finally, if all other components seem ok then you should check out your ignition system which consists of spark plugs, wires and distributor cap/rotor arm (if applicable). Spark plugs should be free from corrosion and firing correctly – if they aren’t firing correctly then they could potentially cause misfires which would prevent your engine from starting up properly too! You should also inspect spark plug wires for fraying/damage – if they’re damaged then this could potentially lead to an ignition issue as well.

If everything else checks out ok but you still can’t get your car started then it could potentially point towards an issue with another part of your ignition system such as distributor cap/rotor arm or starter motor (if applicable). In this case you’ll need an experienced mechanic who can diagnose these parts accurately before attempting repairs on them yourself!


The first thing to check when a car won’t start is the battery. If the battery is dead, there’s no point in troubleshooting any further. Check to make sure the battery has enough charge. If it is low, try charging it before proceeding with other tests.

If the battery has enough charge, then it could be a problem with the connections between the battery and starter or solenoid. Make sure all the connections are tight and free of corrosion. If you find any corroded connections, clean them up and try again.


If all of the connections are good, then check for blown fuses or relays. The fuse panel should be labeled with what each fuse does and where it is located in the car. Check each fuse visually for obvious signs of damage (i.e., melted plastic or metal). If you find a blown fuse, replace it with one of the same amperage rating and try again.

Starter Motor

If all of these steps fail to get your car started, then you may have an issue with your starter motor. To test this, locate the starter motor in your engine bay and have someone turn on the ignition while you listen for any clicking noises that indicate a faulty starter motor. If there are no noises at all, then your starter motor may need to be replaced or repaired by an auto mechanic.

Fuel System

The last thing to check if none of these steps solves your problem is your fuel system. Make sure that you have enough fuel in your tank and that there are no blockages or leaks in your fuel line from tank to engine bay (check under hood). You can also inspect your spark plugs for signs of fouling or wear that could indicate a problem with your fuel system (i.e., not enough fuel getting to cylinders).

FAQ & Answers

Q: What could be the cause of a car not starting when full accessory power is active?
A: There could be a few potential causes for this issue. One of the most common is a weak or dead battery, which can be caused by leaving the lights on or other electrical components running while the engine is off. Other potential causes include an alternator failure, a faulty starter motor, or an issue with the ignition switch or starter relay.

Q: How do I check if my car battery is weak or dead?
A: A simple way to check if your car’s battery is weak or dead is to use a multimeter to measure its voltage. If it reads less than 12 volts, then it may need charging or replacing. You can also check for corrosion around the terminals and inspect any cables for signs of damage or aging.

Q: What should I do if my car won’t start and full accessory power is active?
A: If your car won’t start and full accessory power is active, you should first try jump-starting your vehicle using another vehicle’s battery, jumper cables, and safety precautions. If that fails, then you may need to have your vehicle inspected by a mechanic in order to diagnose and repair the underlying issue.

Q: How can I prevent my car from not starting due to full accessory power being active?
A: One of the best ways to prevent this issue from occurring in the future is by ensuring that all electrical components are turned off before turning off your engine and removing your key from the ignition switch. Additionally, make sure that your battery has enough charge and that all cables are properly connected and free from corrosion.

Q: What should I do if my battery needs replacing?
A: If you have determined that your battery needs replacing due to low voltage readings, then you should take it to an automotive store for disposal and purchase a new one of equal size with similar specifications as recommended in your owners manual. Once you have the new battery installed, make sure that all connections are secure and follow any instruction provided with the new battery before turning on your engine again.

After careful examination of the issue, it is concluded that the reason why the car won’t start despite having full accessory power is most likely due to an issue with either the starter motor or the battery. To diagnose and repair this issue, a qualified mechanic should be consulted.

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