How to: testing Glow Plugs

Car getting harder to start on colder mornings? First thing to check on a diesel with this symptom is the glow plugs and related circuit.

On the Meganes and Lagunas with the push button start, the computer does not give the glow plugs enough time to warm up, so it is vital to have them all working properly and have a strong battery.

To test glow plug circuit.

Get out your multimeter, earth negative on battery negative. Put positive probe on the wire going into a glow plug. Get a friend to crank engine over. You should see a good 13+ volts for a few seconds. If not, check fuses and relays.

To test glow plugs.

Again use your multimeter, this time on ohms/resistance setting. Put one terminal on top connection of glowplug, other one on a good ground on the engine block close to the glowplug. You should get a reading somewhere around the 1 ohm mark. If they glowplug is dead, you will be getting close to infinite resistance, meaning the coil inside it burn out.

The video below shows a similar way to test glow plugs on dci engines…