1. Connect a voltmeter or 12-volt test lamp between the glow plug power wire and "ground" (metal of the body or power unit - grounding must be reliable).
2. Ask an assistant to turn on the ignition and read the meter reading - pay attention to the duration of operation of the pre-glow control lamp on the instrument panel and compare it with the duration of voltage supply to the spark plugs.
At a temperature in the engine compartment of 20°C, the duration of the indicator lamp operation should be 3 s. A decrease in temperature entails an increase in the duration, and vice versa.
If the lamp does not work and there is no power supplied to the spark plugs, the cause of the failure may be the control module or its wiring circuit.
1. To identify a faulty spark plug, loosen the nuts, remove the washers and disconnect the power wire and bus from the spark plugs - on recent models, it is enough to simply disconnect the spark plug wiring connectors.
2. Connect an ohmmeter between the central terminal of the spark plug and the ground - a working spark plug has very low resistance (less than 1 Ohm). If the ohmmeter registers a break (infinite indication), therefore, the spark plug is faulty and must be replaced. Alternatively, you can connect a test lamp between the power wire and the central terminal of the spark plug - turning on the ignition with a working spark plug should activate the lamp.
If you have an ammeter at hand, you can measure the current flowing through each spark plug. After the first pulse with an amplitude of 15-20 A, the current should drop to 12 A. If the measurement result goes beyond the permissible range, the corresponding spark plug must be replaced.
Finally, the spark plug can be removed and checked according to the instructions (see Removal, checking and installation glow plugs).
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