Test condition: the battery must be fully charged, the battery voltage must be at least 12 V. The engine is cold (ambient temperature) or the engine temperature must not be higher than 55°C. At higher temperatures, disconnect the coolant temperature sensor connector.
Checking the power supply
This check can be performed without removing the glow plugs.
Connect the voltmeter to the current bus of the glow plug keys and the spark plug body.
Turn on ignition. Warm up the engine (preheat). The voltmeter should show battery voltage (9 V or higher) for about 3 seconds. The time depends on the glow plug temperature and battery voltage.
Start the engine and let it idle. During the start and for about 180 seconds after that, the voltmeter should indicate battery voltage (9 V or higher).
If there is a power failure, have the pre-heater control unit checked at a specialist workshop.
Checking glow plugs
Check the current busbar for corrosion, otherwise clean or replace.
Check the glow plug for any external visible damage.
Remove the connection wire and the current bus.
Measure the resistance between the glow plug contact and the glow plug body with an ohmmeter. The required value is about 0 Ohm. If the resistance is 00, replace the glow plug.
Check all glow plugs in the same way.
Note: Normal spark plug resistance is very low and difficult to measure with conventional ohmmeters. Required value: 0.235 Ohm. Clean the spark plug from oil before measuring.
Connect the wire and the current bus.
If it was disconnected, connect the coolant temperature sensor connector.
Note: If no defect is found, although the engine continues to start poorly, perform an external inspection of the glow plugs during warming up. To do this, remove the injectors and observe the glow plugs through the holes.
Glow plugs with burnt heating rods
Burnt glow plug rods are often caused by faulty injectors. Such damage should not be attributed to an internal or external defect in the glow plug.
If such glow plugs are found -arrow-, it is not enough to replace them. In this case, it is also necessary to check the injection nozzles for injection pressure and tightness (workshop work).