The best way to check the health of system components is to replace them with known-good ones. However, there are a few tests that make sense to do first.
1. Connect a voltmeter or 12-volt test lamp between the glow plug power wire and «weight» (body metal 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 the operation of the preheat control lamp on the dashboard and compare it with the duration of the voltage supply to the candles.
At a temperature in the engine compartment of 20°C, the duration of the operation of the control lamp should be 3 s. A decrease in temperature entails an increase in duration, and vice versa.
If the lamp does not work and there is no power to the candles, the cause of the failure may be the control module or its wiring circuit.
1. To identify a faulty candle, give the nuts, remove the washers and disconnect the power wire and bus from the candles - on models of recent years of production, it is enough to simply disconnect the plug connectors of the spark plug wiring.
2. Connect an ohmmeter between the center lead of the spark plug and «weight», - a serviceable candle has a very low resistance (less than 1 ohm). If the ohmmeter registers an open (infinite reading), therefore, the candle is faulty and must be replaced. Alternatively, you can connect a test lamp between the power wire and the central output of the candle - turning on the ignition with a good candle should lead to the activation of the lamp.
If you have an ammeter on hand, you can measure the strength of the current flowing through each candle. After the first pulse with an amplitude of 15-20 A, the current strength should drop to 12 A. If the measurement result goes beyond the allowable range, the corresponding candle must be replaced.
In conclusion, the candle can be turned out and checked, guided by the instructions (see Removing, checking and installing glow plugs).
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