The purpose of this test is to evaluate the condition of the glow plugs based on the total current draw, while also confirming their operation time.
Connection for diagnostic work will vary dependent on application.
Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.
General connection advice
PicoScope offers a range of options within the test kits.
Dependent on difficulty of access, choose from:
Testing sensors and actuators (to include relevant circuit/connectors):
This known good waveform has the following characteristics:
There is a current spike to around 100 A as the glow plugs are switched on. The current then immediately falls to around 70 A, followed by a downward curve indicating the time taken, 1.5 s, to heat the glow plugs to maximum. The operating current then remains stable around 50 A until control switches the glow plugs off. Total on time is 11 s.
In order to ignite diesel fuel the air temperature during compression must reach the critical temperature of 850° C.
With cold ambient temperatures, intake air and engine components, this may not be achieved.
In these circumstances glow plugs are used to heat up the combustion area to aid starting.
Glow plugs are also used to improve the cold running of a diesel engine thereby improving emissions.
They are designed to operate within a glow temperature of 850° to 1100° C.
Glow plugs may be controlled either by the Engine Control Module (ECM) or by a dedicated glow plug control unit/timer.
Use the vehicle data to identify system switching and on time characteristics.
One of the main causes of glow plug failure is overheating.
In order to prevent overheating and allow operation during engine running the majority of glow plug systems now use Pulse Width Modulation (PWM) as a method of control.
It is important to be able to identify “control” failure as a cause of glow plug failure.
Other causes of glow plug failure can be;
Characteristics of failed glow plugs;
The operating current can be calculated using the wattage rating of the glow plug. This rating is available in the appropriate diesel data books.
Once you know the wattage, multiply it by the number of cylinders and then divide by the voltage to calculate the expected final current.
Selection of component-related Diagnostic Trouble Codes (DTCs):
P0380 - Glow Plug/Heater Circuit "A" Malfunction
P0381 - Glow Plug/Heater Indicator Circuit Malfunction
U0106 - Lost Communication with Glow Plug Control Module
U0307 - Software Incompatibility with Glow Plug Control Module
U0407 - Invalid Data Received from Glow Plug Control Module
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.
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