The objective of this procedure is to show you how to check a starting system. DVOMs come in many forms. Always follow the specific manufacturer's instructions in the use of the meter or you could seriously damage the meter or electrical circuit.
Part 1. Preparation and safety
Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:
- Work clothing - such as coveralls and steel-capped footwear
- Eye protection - such as safety glasses and face masks
- Ear protection - such as earmuffs and earplugs
- Hand protection - such as rubber gloves and barrier cream
- Respiratory equipment - such as face masks and valved respirators
If you are not certain what is appropriate or required, ask your supervisor.
- Make sure the hood stay rod is secure.
- Always make sure that you wear the appropriate personal protection equipment before starting the job. It is very easy to hurt yourself even when the most exhaustive protection measures are taken.
- Always ensure that your work area/environment is as safe as you can make it. Do not use damaged, broken or worn out workshop equipment.
- Always follow any manufacturer's personal safety instructions to prevent damage to the vehicle you are servicing.
- Make sure that you understand and observe all legislative and personal safety procedures when carrying out the following tasks. If you are unsure of what these are, ask your supervisor.
Points to note
- DVOMs come in many forms. Always follow the specific manufacturer's instructions in the use of the meter or you could seriously damage the meter or electrical circuit.
Part 2: Step-by-step instruction
- Set up the meter for a voltage check
Prepare the Digital Volt Ohm Meter or DVOM for testing for voltage by inserting the black probe lead into the “common” input port, and the red probe lead into the “Volt/Ohms” input port.
- Check the meter function
Turn the rotary dial until you have selected the mode for “Volts DC”. The reading on the meter should now be at Zero. Some meters will automatically sense the correct voltage range for the meter when a voltage is detected. On other meters you will have to set the voltage range before using the meter.
- Check the battery voltage
Place the Black probe onto the Negative terminal of the battery, which will be marked with a Minus sign, and place the Red probe onto the Positive terminal of the battery. This is marked with a Plus sign. Note the voltage reading from the battery.
- Disconnect the ignition system
With the meter still connected to the battery, disconnect the ignition system. Usually, simply disconnecting the coil lead, or alternatively, disconnecting the spark plug leads, will ensure the vehicle will not start when you turn the engine over with the starter motor, which is known as ‘cranking’ the engine. Choose a method suitable for the type of ignition system in the vehicle you are working on. In most modern vehicles, it is better to allow the ignition spark generated by cranking the engine to have some safe alternative place to go.
- Crank the engine and check result
Crank the engine whilst at the same time watching the voltage displayed on the DVOM. This test checks the starter circuit for voltage drop, and gives a good indication of the condition of the starter circuit voltage. If the reading remains above 10.25 Volts then the system is in good condition. If the reading is below 10.25 Volts then this may indicate a fault with the starting system and further investigation is required.
- Starter motor electrical connections
If the required voltage is present at the solenoid motor terminal, any problem may be in the starter motor or its cabling. If the original test indicated normal voltage, but slow or no cranking, check the motor system and its connections. If the drive pinion keeps shifting out of mesh with the flywheel, check for a broken or a loose external ground wire on the solenoid. Replace a broken wire or reattach a loose one. Place an ammeter in the circuit to measure the amp in either the positive, or ground cable of the starter motor. With the ammeter in place, press the start switch. If the amp draw is excessive, according to the manufacturer’s specifications, then the starter motor is probably faulty. Before you replace the starter, check the condition of the engine to make sure it turns freely. An engine in poor condition could cause the starter to work harder, and may have been damaged by the engine’s poor condition.