How to Diagnose Faults on a RC Car

By Joe Rich

How to Diagnose Faults on a RC Car

If you have ever been ready to get out with your RC car for a bash only to find that your model is not working as it should then How to Diagnose Faults in a RC Car should get you back on track.

You know that feeling when you want to get out with your RC car to have some fun but it doesn’t work at all?

It’s really frustrating.

So here is How to Diagnose Faults on a RC Car

Most of the time, it may be something as simple as forgetting to turn on the transmitter.

On other occasions, however, it may be something more complex.

If you are unable to get to your local hobby shop for help or do something drastic like plan on getting another RC car just hold on a sec.

If your RC car fails to work, this article could help you on how to diagnose these faults and you could learn how to fix some of them?

You don’t need to be an expert to fix some of the common problems affecting your RC car.  Having some basic knowledge on how it operates can allow you to diagnose the problem, fix it and even know when to hand it over to an expert for those more complicated repairs and adjustments. So let’s get to it.


How to Check Electric Power and Switches.

A common fault that can cause your RC car to fail to work is faulty batteries.

When a RC car is running a bit sluggish it might be an indication that the batteries have a problem.

If your batteries are not charging, it means they are most likely defective and need to be replaced.

There are several ways you can diagnose a battery problem.

First, be sure to check for any missing batteries.

Look in both the transmitter and the RC car to make sure all the batteries have been installed.

It is very common for these to be overlooked.

You also have to check that each of the batteries has been installed in the right position.

Most of the time, the direction is usually given on the battery seating so that you can ensure that each battery is well placed.

You can always replace the batteries if they’re old.

If your RC car uses a battery pack, take it out and test it to make sure that it is working.

If you have not used your RC car for a long time, there’s a good chance that the battery slots are corroded due to exposure to air and moisture.

Make sure to replace the batteries and clean the battery links before using it again.

As previously mentioned, sometimes the reason why your RC car is not starting is forgetting to turn on the transmitter.

Don’t worry, a lot of people make this mistake.

First check the switches and turn the switch on.

If this does not work, the switch itself might have a problem. Remember to ensure that the RC car switch is off before working inside your car.

How to check if Power is getting to the Motor and Servos.


If the steering is unresponsive it may be something as simple as over tightening of the steering connecting rods.

Disconnect the servo and see if the steering is moving freely if not just slacken off any screws.

Remember not to over tighten the servo retaining screw.

Sometimes, your RC car might only respond to some commands such as turning the wheels but not being able to move forward.

This might be as a result of the motor and servos receiving little or no power at all.

You will need to check if enough power is getting to the motor and servos.

One major cause of lack of power reaching the motors or servos is melted wires.

Sometimes, a large current flowing through these wires can cause them to melt and in turn reduce the current that the motor or servo receives.

If this is the case, you will need to replace the connection with new wires.

Since the ESC controls the amount of current entering the motor, you can test whether it has a problem using a different motor which you know works well.

If the motor works, then the ESC is just fine.

Be sure to check the wire connection between the ESC and the motor and on the servo for any loose connections and reconnect if needed.

You can also use a voltage meter to see if there is a problem with the servo. Measure the amount of voltage on the servo contact points. If it’s way below 6 volts, it’s not getting enough voltage to operate fully.

How to check motors for faults including burn outs and seizing

Motors are an important part of the operation of any RC vehicle.

A common problem that affects RC car motors is burning out.

This usually happens as a result of overloading, too much current entering the motor and overheating in the process.

Sometimes it is a bit difficult to determine what is causing the motor to burn out.

You will know when your motor is burning out as you might notice a burnt smell coming off the car.

This is an indication that the motor brushes are worn out for a brushed motor.

You can observe the temperature limits within different parts of the RC car to narrow down the cause of the motor burning out. Using a temp gun,  if yo have one you can observe the following limits:

  • Motor :160F
  • ESC :140F
  • Battery:120F

You can also remove the motor and take out the commutator brushes.

If they appear to be slightly burnt, then it won’t take long for the motor to burn out completely.

Be sure to clean them off before returning them back to the motor.

If your motor stops spinning or spins for only for a short time, then it’s seizing.

This seizing can be caused by a variety of factors such as foreign objects within the motor or even a broken magnet.

You will need a good visual inspection or if possible on your motor is to tear apart the motor to know what exactly is causing it to seize.

You can easily remove the foreign objects but if it does have a broken magnet, you might need to replace the motor.

You can easily find a motor replacement at a Hobby Shop near you or at here at amazon.com .

If you’re still unsure what is causing your motor to fail, you can always check the ESC. Run some benchmark tests with the ESC to see how it performs.

How to check drive shafts and bearings.

A bent drive shaft can easily cause damage to the front differential and motor mount bearings.

 You should always check for bends in the driveshaft before taking your RC car out for a bash.

For centre couplings and drive pins, you should remove them from the car, inspect them for wear and replace from time to time.

It only takes a few screws, four, to remove the driveshaft.

Sometimes it may require you to disassemble the whole drive train to check the driveshaft.

In this case, you will need to first remove the gearbox from the chassis.

For 4WD cars, you’ll have to take out the centre driveshaft followed by the dog bones and drive cups.

Once you remove the driveshaft, flush it with solvent to remove any contaminated grease.

Look for any bends in the shaft and worn out parts in the cross pins.

If your RC car uses sliders, make sure to look if any of them are twisting.

Twisting sliders are hindered from moving freely once the drive train starts spinning.

Remember to look for notches on the drive cups since this can cause binding on the drive train and eventual failure.

To ensure proper bearing operation, test whether the ball bearings can spin freely and smoothly.

Upgrade plastic bearings for steel

Since they are essential in reducing friction, they have to be as clean and smooth as possible.

If you drive in wet conditions, there’s a chance that the bearings are rusted.

If this is the case, you might need to replace them.

If your drive line is binding, you can first spin the wheel hubs or carriers to see if there’s any binding.

These typically have two bearings per point.

Do this on all sides of the hubs and carriers.

Now test the centre drive line including all differentials for binding as you clean and test each bearing if it can spin freely.

The most ideal bearings to use when replacing are single sided rubber sealed bearings.

With one side with a rubber seal, they can prevent entry of that into the bearing so when replacing the bearings be sure to place the rubber side where dirt is most likely to enter. They are also relatively inexpensive as they come in at about $1 per bearing.

How to check for faulty differentials.

Differentials are one part of your RC car that requires proper maintenance.

There are two types that are mainly used: the ball and gear differentials.

For maintenance of a ball gear, you will need to completely disassemble the whole unit after removing it from the vehicle.

One of the most common mistakes that lead to differential failure is over-tightening the differential.

A differential that is too tight will cause the balls to mark the grooves thus damaging the balls and the differential plate itself.

It will also put more pressure on the bearings which will wear out easily.

Be sure to check for gears with missing teeth and gritty or damaged bearings.

Remember to clean all components with a degreaser.

In order to detect excessive wear, run your fingernail across the groove in which each diff ball rides.

If it feels a bit too deep and uneven, you might need to replace it and the diff balls.

Don’t worry, you can find these parts in a differential rebuild kit.

During reassembly, use a dab of differential grease when lubricating the differential balls.

The thrust balls and cage will need thicker grease during lubrication.

Reassemble the differential before reinstalling it and readjust the slipper clutch.

Gear differentials, on the other hand, are a bit easier to maintain as they have less parts.

You just need to remove the housing, open it up and use solvent to remove any grease. Then check for wear on the gears and then lubricate with fresh grease.

Motor Differential and Bearings

So basically, those are all the checks you need to do on your RC car when you suspect it has a fault.

Some of them are easy to rectify while others will require you to take your car to the Hobby Shop.

Don’t let a single fault ruin your racing days.

Related articles

What is a RC car servo (a complete guide)

How to break in a Nitro engine (a complete guide)

What is a Transmitter and how does it work.

Difference between brushed and brushless motors.

What is a ESC for a RC car

How to service and maintain your RC nitro car

Click here to view RC Car batteries on Amazon

Click here to view RC Car servos on Amazon

Click here to view RC Motors on Amazon

Click here to view RC Car drive shafts on Amazon

Click here to view RC Car bearings on Amazon