How to test a starter motor

How to test a starter motor
How to test a starter motor

Starter motors have a hard job, and I have owned many cars where the starter motor has eventually needed to be changed. 

What normally happens is that you will jump in your car to go somewhere important, turn the ignition key and all that you here is a clicking noise and the car won’t start. Often, you may not hear anything, the dashboard lights come on but the car will not start.

Before you go ahead and strip the starter motor off the car, make sure that you have checked that the alternator and the battery are working correctly. Also make sure that you have checked that all of the wiring to the starter motor is securely in place. We recently had a Land Rover Freelander that would not start, turned out to be a bad spade connection fitted to the back of the starter.

In the past, I have changed a starter motor and an alternator only to find out that it was a faulty battery causing my starting problems. Also check that all the wiring to the battery, alternator and starter motor (including solenoid) are secure and that there is no corrosion on the terminals.

We will assume that all the other parts of the cars electrics are working fine and that you have already removed the starter motor from the car. See article, how to change a starter motor.

Starter motor basics.

The purpose of this starter motor unit is to start the movement of the engine when you turn the key in your ignition.  Here is a typical arrangement of a starter motor. The large cylinder on the bottom is the actual starter motor and the smaller cylinder on top is the solenoid.  The entire unit with both parts is referred to as the ‘starter motor’.  See the toothed gear on the left, this is what turns your engine to get it started. There are 2 actions of a starter motor unit, the first is to push that toothed gear forward so that it meshes with the engines flywheel, and the second motion is the rotating of that toothed gear so that it turns the flywheel/engine.  This is how all car engines are started.

How to test a starter motor.
This is a basic ‘bench test’ of the starter motor and solenoid off the vehicle. It is a basic test that should be done before you fit a starter motor, especially if you have purchased one from the scrapyard.

There are other methods of starter motor troubleshooting, these are more indepth and are not covered in this article. We have updated the video below and it shows how to test the operation of both the starter motor and solenoid – take a look.

Price up a starter motor for your car

What you need to test a starter motor ;
A well charged battery,
A set of jump leads.

During these test it is quite common for large sparks to be produced. Make sure you are in a clear area where there are no flammable liquids or other materials.
There is too much torque, the safest thing is to mount it in a vice if possible.

Testing the solenoid.
The Solenoid (small cylinder on top) controls the movement of the ‘starter motor pinion’ or the toothed gear that can been seen through the cutout. Connect the black jump lead to the negative (-) terminal of the battery and the other end to the body of the starter motor.

Now connect the red jump lead to the positive (+) terminal of the battery and touch the other end of the lead to the terminal on the back of the solenoid.  The solenoid should click loudly and throw the starter motor pinion forward.  The starter motor should not turn.

If this does not happen, then the solenoid is faulty.

Testing the starter motor.
Touch the end of the red jump lead onto the large terminal of the starter motor. The shaft should rotate strongly, if no then there is a fault and the entire unit should be replaced.

This video shows the starter motor being tested.
One more time Always take great care when testing a starter motor. These things produce massive forces, so don’t try and hold it in your hand when you are operating them. They are designed to turn engines, so don’t think you can hold one still easily.

How to charge a car battery

How to charging a car battery.  They go flat for lots of reasons, here are a few ;

* Battery getting old
* Car has been standing for a while
* Alternator not charging
* Lights have been left on
* Very cold weather

Car battery chargers ;
* Are really easy to use
* Are cheap
* Save you lots of hassle
* Save you money (on new batteries)

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How to charge a car battery
This is a typical car battery charger


* Battery charger,
* Spanner (usually 10mm or an Adjustable),
* Up to 8 hours charge time (overnight),
* Possibly some distilled or de-ionised water.

If your car is parked close enough to your house or in a garage, then you can leave the car on the battery whilst it is charging.  However, you must disconnect both red and black battery terminals (probably with your 10mm spanner) ;

Removing a Car Battery
How to Remove a Car Battery from your Vehicle

If it is not, then you will have to take the battery off the car, so watch the video below to see how easy it is.


Once you have taken off the battery, take it to a safe area with plenty of ventilation and away from kids, pets, naked flames and sparks.

Check the labels on the battery to see if you need to remove any of the ‘cell caps’ whilst charging the battery.

Some batteries are sealed units and do not have these, but if yours has ‘cell caps’ they will be situated on the top, they are normally under a press-on strip, others will be circular caps for individual opening (see pics below).

car battery charging

car battery top

This battery has caps under the yellow  strip

This battery has the individual caps

car battery cell caps removed
This battery has had the cell caps removed.

Either remove the press-on strip or individual round caps before connecting the battery charger.  This will allow any gases created during charging to escape and not build up inside the battery – this is why you need to put the battery in a well ventilated area.

car battery on charge
Typical car battery being charged.


BEFORE YOU CONNECT – Before you connect the battery charger, you will need to check the levels inside the battery – this is very easy.  If they are low, then you need to top up the cells with ‘distilled’ or ‘de-ionised’ water, this is the stuff you are supposed to use in your iron, so it is available from the supermarket in the laundry section.  My recent bottle cost 60p. DO NOT USE TAP WATER, under any circumstances do not use tap water, it will damage the cells inside the battery and you will have to buy a new battery.

I recently had to top up my car battery with distilled water before I charged it up. It only cost me 80p for a bottle, and I got it from my local corner hardware shop.  That 80p saved me the cost of a new battery.

It is important to ensure that the metal plates / cells inside the battery are covered with electrolyte. DON’T PANIC, electrolyte is just the mixture of acid and distilled water inside the battery and if the cells are not covered by the electrolyte liquid they will get damaged and you will need a new battery.

inside car batterycar battery electrolyte
Here are a couple of drawings showing the inside of the battery and the cells / plates that need to be covered by the electrolyte.

How to charge a car battery
Checking inside car battery cells

All you need to do once you have removed the cell caps is have a look down inside all of them (ideally use a small torch) ;

Looking into the cells, you can see they have
been filled so that the plates are covered with the electrolyte.

Most batteries have a minimum fill level when you look inside them, so topping up is very easy and very cheap.  DO NOT ignore the importance of topping up your car battery, it can save you ALOT OF MONEY.

If you are leaving the battery on the car then disconnect the negative (black) and positive (red) wires from the battery using the relevant spanner (usually 10mm).

Before you go any further, make sure you have read the manufacturers instructions that come with the battery charger.

With the battery charger unplugged from the electricity supply, connect the black charger clip to the negative ( – ) terminal of the battery and the red clip to the positive ( + ) terminal.

Now plug the car battery charger into the mains and switch it on.

Leave the battery charging overnight and when you check on it in the morning the charger should indicate that the battery is fully charged.

Switch off and then unplug the charger, remove the charger clips from the battery and refit the cell caps / strip.

The battery should now be ready to refit to the car, follow the removal instructions in reverse.

THEN, start your car – AND OFF YOU GO

and you will also be bending over, so if you have back trouble, be more careful and perhaps get someone to help you with the lifting.

Topping up your battery with distilled water – Some battery chargers will show when the battery is full. But if you know the battery to be flat but the battery charger is showing it to be full.  Make absolutely sure that the battery is topped up enough.  (I recently had to charge a car battery and thought I had put enough distilled water in it but when I connected the charger, it said that it was fully charged.  So I added some more distilled water to all of the cells and then the FULL LED on the charger went out and the charger started doing its work). If the battery is correctly filled and the charger is still saying full, chances are that the cells in the battery are damaged and you will need a new car battery.

If your car battery keeps going flat, then there is something wrong, possibly with the battery or the alternator or something else. Check out the rest of our HOW TO articles to test other parts.

NOTE – make sure you always read the manufacturers instructions for all equipment and appliances.

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How to test your alternator

car alternatorTest car alternator Car alternator, if you don’t know what one is then take a look at our article what is an alternator. Your car alternator will not last forever, and when it does go, it can leave you stranded somewhere with a flat battery – and no-one needs that.

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Not everyone has breakdown cover. Perhaps you currently have car problems (battery keeps going flat) and you think it may be that the alternator is to blame !! Whatever your current situation, testing your alternator is a quick and simple job and something you should do to keep your car tip-top and reliable. You don’t need to take your car alternator apart to test it and you don’t need any expensive tools. What you will need (buy one, they are cheap or borrow one) is a volt meter or multimeter. They are very simple to use, here is a photo of one (cost about £10) ; Here is what you do, simple car alternator test ; Make sure all the accessories on your car are turned off (lights, radio etc.) and then rev up the cars engine to a fast idle (say 2000-2500 rpm). Set the volt meter or multimeter to the DC scale and measure the voltage across the battery terminals – red lead of the voltmeter on the positive terminal, black on the negative. You will need someone to rev the engine whilst you connect the meter to the battery. With the engine at a fast idle, the voltage on the meter should read around 14 volts (13.5 to 14.4). The alternator needs to generate a larger voltage than the battery’s rated voltage to overcome the internal resistance of the battery.

The current needed to recharge the battery would not flow at all if the car alternator output voltage was the same. The larger the difference between the alternator output and the battery voltage, then the quicker the battery will charge.

So as you can imagine, if your car is quite old and the alternator and the battery are too, problems can occur with the battery getting enough charge and making the car more difficult to start and less reliable.

If the reading on the multimeter is less than 12 volts then you may have a failed alternator.

Even if you have to buy a Haynes Manualmultimeter and some spanners, it will still probably cost you less than having a garage do the work.

The alternator is bolted to the side of the engine and is driven (turned) by the engine via a belt.  The belt turns a shaft inside the alternator when the engine is running and the output (voltage) is sent to the battery via wires. 

Many places sell brand new replacement alternators as well as refurbished or reconditioned alternators.  A reconditioned alternator has had all the internal wear parts such as brushes replaced with new ones. They will have been tested and will come with a guarantee, so don’t worry about using one of these, they are good as new and cheaper. I have also fitted second hand (used) alternators to a number of my cars. These have been sourced from scrap yards or vehicle dismantlers. They normally come with a receipt and can be changed within a short period of time if they turn out not to be working. I have always asked the supplier to test the alternator before I have paid for it. When buying parts it is always very important to keep the receipts incase a problem occurs. Receipts are always worth keeping as they show a history of your car which prospective buyers like to see when they are thinking of buying your vehicle.

If your garage ever tells you that you need a new 
alternator, ask them ;

a) have they performed a load test on it ?
b) what were the voltage readings ?
c) was the alternator belt worn or slipping ?
d) was there excessive noise from the alternator

These simple questions will let your mechanic know that you know a bit more about your cars electrical system than just how to turn the lights on. This should mean that you get given the best service and are treated better by the garage and not feel like you have been ripped off when work is done to your car.

Consider some breakdown cover to annoying eventualities like this.  Have a read of our unbiased reviews of the car breakdown services currently available (opens in new window).

This clip shows the sound that your alternator should NOT be making if it is working fine.

One more check ;
Next, turn on the heater, the rear window de-mister, the radio, the headlights and anything else that draws power from the battery.

Now rev up the engine again and look at the multimeter .

It should still be reading around 14 volts. If it reads lower than 13 volts the chances are that the alternator is faulty and will need to be replaced before it catches you out.

What to do if the alternator has failed
Replacing an alternator is not a difficult job, however it varies from car to car as to how difficult the alternator is to access and remove the belt. If you purchase a Haynes Manual (cost about £13), then it will show you with instructions and photos how to undertake this change on your specific car in the easiest way and it will tell you what tools you need.

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Jump start a car • How To


If your car won’t start because the battery has gone flat, then you may be able get it going again by jump-starting it.

‘Jump Starting’ is the method of using battery power from another vehicle to start your cars engine by the use of ‘Jump Leads’.

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What you need ;
1) A set of car jump leads, also referred to as booster cables
2) A friends car that is working.

Using jump leads is pretty simple and safe if you follow these instructions ;

1. Position both of the cars close together so that the jump leads will reach both batteries.

2. Then connect the car battery booster cables in this order ;

a. Connect (+) positive red cable to the (+) positive terminal on the dead battery.
b. Connect the other end of the (+) positive red cable to (+) positive terminal on the working car.
c. Connect (-) negative black cable to (-) negative terminal on the working car.
d. Connect the other end of the (-) negative cable to the (-) negative terminal on the dead battery.

3. You are now ready to start the working cars engine.  Turn off all electrical equipment on the working car (heater, lights, radio, etc.) so that all the battery power is getting used to jump start the dead battery. Let the working car run for a minute or so before you try to start the dead one. Revving the engine in the working car will produce more power and help with jumping the dead battery.
4. Now try and start the dead battery engine by turning the ignition. If it sounds like it is going to start but will not quite go, then rev the working car for a little longer before trying the dead battery again.

5. When the dead battery has started and is running, remove the jump leads.

Do this in reverse order ;
a. Disconnect (-) negative black cable from the terminal on dead battery.
b. Disconnect (-) negative black cable from the (-) negative terminal on the working car.
c. Disconnect (+) positive red cable from the (+) positive terminal on the working car.
d. Disconnect (+) positive red cable from the (+) positive terminal on the dead battery.

1) You must let the car that had the flat (dead) battery run for quite a while.
If you turn the ignition off shortly after starting it then it may not start again because there will not be enough charge in the battery. It might be worth taking the car for a drive, or driving the car home and connecting the battery to a battery charger overnight.

2) Ensure that when you are connecting and removing the jump leads, they do not touch each other and do not come into contact with any moving parts on either engine. Most quality jump leads have the clamps coated with plastic so there is less chance of the metal parts touching parts of the car or engine. This is something to consider when buying your jump leads.

3) If the car will not start after following this procedure, then it may be time to get the battery replaced.  It is suggested that you try replacing the dead battery with a borrowed one before you spend money on a new one because the fault may be somewhere else, such as the alternator.  Alternatively, get an auto-electrician/mechanic to check the vehicle over for you.

4) Car battery booster cables are always a useful thing to have on your car, whether to help you out of trouble and get you on your way, or to give someone else a helping hand. They are relatively inexpensive, and buying a set to keep in the back of your car is well worthwhile when compared to the inconvenience of having a flat battery. They can be purchased from any local motor-factors, or bought online from most car accessory websites.

As well as jump leads, there are a couple of other useful items that perhaps you should stick onto your Christmas or birthday wish list ;

1. Car battery chargers.
Click image for more info.
Keep this at home and if you ever suffer a flat battery on your car you can bring it into the house and recharge it overnight. The battery charger plugs into your house electric supply and has a black and red clamp for fitting onto the (+) (red) and (-)(black) of your battery. Car battery chargers normally take 12-24 hours to recharge your car, they will recharge slowly and normally let you know when the battery is full.

2. Battery booster packs.
Click image for more info.
Keep one of these on charge in your garage, and whenever you suffer a flat battery this will get you started. Inside it is a large battery and it also has (+) and (-) clamps. Keep it plugged in when it is not in use and then it will always be fully charged. Just attach it to your dead battery and it should provide enough power to start your car. Just remember to keep the car running until your engine has recharged the cars battery.

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