Test Tools


MultimeterMultimeters are a must have tool when working with electronic systems.
The meter will need to read DC Voltage and Ohms (resistance); most meters also read AC Voltage, Amps (DC & AC) and diode tests, although these features are useful they are less relevant that DC Volts and Ohms. If possible use a self ranging meter as these are just much more user friendly.
Most meters also have a Continuity test or Continuity buzz test which is useful but be careful using this for circuit testing as surprising high (in circuit resistance terms) can trigger the continuity buzz. Continuity in basic terms means an electrical path is present. This is not overly useful when testing anything other than an open circuit. When testing electrical circuits it is the integrity of the circuit that is important, perhaps total circuit resistance less that 1 ohm, not much use using the continuity buzz test if the continuity buzzer will be trigger at 10-20 ohms. Considering that thin wall automotive cable of 1 mm CSA has a resistance of approx 20 Ohm/Km at room temp, a circuit resistance of 10 – 20 ohms (which is blind to the the continuity buzz) is similar to adding 750-1000 meters of cable to the circuit.

Test lamp

Test lamps are a very useful and simple tool to use. Test lamps can confirm that there is both voltage and current at the point being tested; that is to say that there needs to be sufficient voltage and current at the test point for the bulb to be illuminated. This is an interesting point, unlike a multimeter when used for taking voltage measurements, the test lamp requires current to flow in the circuit. This can be used to the testers advantage, for example, a test lamp can be used to trigger the contact coils of a relay, but it should also be remember that because of the potential for current flow test lamps should be used sparingly or better advice not at all on circuits contenting electronic circuits. The current flow through the test lamp can damage low voltage / low current electronic device. Another useful quality about the test lamp it that it can be used for either positive or negative voltage testing, just simple reverse the polarity of the connections. Test lamps are really a simple guide to the state of a circuit, and the results tend to be ‘binary'; there is / isn’t voltage etc. They will not offer meaningful information about the level of voltage (10volts may illuminate the bulb the same as 12volts) or earth paths.


Oscilloscopes very useful for monitoring control circuits but they can be tricky to use as you need know a little about the characteristics of the circuit or sensor being tested to set the oscilloscope.
Oscilloscopes can be expensive for the better quality units but it is possible to buy PC based Oscilloscopes for less than £75 which considering that the hourly rate for a garage is in the £50-75 range a budget ‘scope might be a sound investment (cost circa 2015). The number of channels (inputs) of the ‘scope is also important, a single channel input will be of limited use as normally more than one circuit is being monitored. General a 3 or 4 channel ‘scope will be fine.
Within the world of automotive engineering high end ‘scopes are the norm, but for the propose of this website we are using a PC based ‘scope purchased online for under £75.

OBD Scan ToolScan tools are very important when working with modern vehicles. Scan tools plug into the vehicle’s OBD diagnostic socket. The amount and type of data which can be read will depend on the vehicle and the sophistication of the scan tool. Basic scan tools will only read engine OBD DTCs, more sophisticated scan tools can not only read and reset engine DTCs but also can access other vehicle systems such as gearbox, body (e.g HVAC), chassis (e.g ABS). The sophisticated scan tools can also read live vehicle data such as, from the engine, current coolant temp, throttle pedal setting, rpm, ignition timing etc and again dependant on the scan tool specification can read live data from all vehicle systems. All scan tools need a diagnostic lead that plugs into the generic vehicle diagnostic socket. The exact spec of the scan tool required will depend on the individual’s requirements but it should be said that one of the minimum requirements must be to reset DTCs and read  set DTCs. The advanced scan tools have the ability to read the ECU’s desired values; these are the values the ECU is trying to achieve by controlling the control systems e.g the turbo charger wastegate. When fault finding a ECU controlled fault the ability to read the ECU’s desired values is very useful when measuring the actual vehicle current value, but this is very much a fault based requirement.
Purchasing of scan tool is probably split into 2 choices, A) A tool to fault find a specific fault, B) a more generic scan tool for more than one use, such as a workshop or fleet operator.