Analog meters may apply higher voltage to the circuit than the digital meter, so use them with care. [2] X Research source The first reading you get from a digital multimeter may not be accurate, since the current can fluctuate. Digital multimeters have a difficult time measuring current that is constantly changing. [3] X Research source Because analog multimeters have a changing display, they can show you the current fluctuations. However, analog multimeters are less accurate overall. It is best to use a digital multimeter for this test. A digital multimeter shows the exact number result of the test. An analog multimeter is harder to read because every possible result is listed at the top. [4] X Research source If you are using an analog multimeter, make sure to choose one with at least 20k ohm/V sensitivity. [5] X Research source
Subtract this amount from the glow plug reading.
If this is not the case, check your battery or alternator before proceeding. Glow plugs will not work correctly if they do not have the correct voltage running into them.
Look at the connector and pins for any signs of rust or corrosion and looseness. Take this opportunity to clean them.
Consult your owner’s manual to find the exact locations of the ground points.
If the multimeter’s negative lead is still connected to the negative battery terminal, then you can leave it there.
Subtract the resistance value of your multimeter from the resistance value of your glow plug. For example, if your plug’s resistance measured . 9 ohms and your meter’s resistance measured . 2 ohms, the real reading for the plug is . 7 ohms. [6] X Research source All the glow plugs in your engine should have similar readings. One glow plug with a higher resistance can affect your engine’s performance–even if the plug is still good. [7] X Research source
Some manufacturers have special tools to clean out the bore where the glow plugs are inserted into the cylinder head. These tools clean out carbon buildup in the area inside the combustion chamber or precharge chamber. The tool also cleans the threads that the glow plug screws into. This tool is sometimes called a “reamer. “[9] X Research source
Subtract this amount from the glow plug reading.
Subtract the resistance value of your multimeter from the resistance value of your glow plug. For example, if your plug’s resistance measured . 9 ohms and your meter’s resistance measured . 2 ohms, the real reading for the plug is . 7 ohms. All the glow plugs from your engine should have similar readings. One glow plug with a higher resistance can affect your engine’s performance–even if the plug is still good. [10] X Research source
