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ABS Speed Sensor
Air Flow Meter / Sensor
Air Intake Pressure Sensor
Alternator Current and Voltage
Amplifier Earth
Camshaft Sensor
Carbon Canister Solenoid Valve
Crankshaft sensor
Coolant Temperature sensor
Diesel Glow Plugs
Digital ECM to Ignition Amplifier Signal
Distributor Pickup
Dual Trace
Electronic Fuel Pump
Exhaust Gas Recirculation
Idle Speed Control Valve
Knock Sensor
Lambda Sensor
MAP Sensor
Relative Compression
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Diesel Glow Plugs/Timer Relay Diagnostics

This test is conducted to evaluate the condition of the glow plugs and to measure the 'on time', which is controlled by the timer relay.

A typical glow (or heater) plug will have a high initial current draw that will gradually drop, stabilising at a constant amperage. The current draw will be dependent on the wattage rating of the glow plug. This data is available in the appropriate diesel data books.

Once the wattage has been ascertained, multiply it by the number of cylinders and then divide by the voltage to calculate the expected stabilised current.

The length of time that the glow plugs are operational can be measured from the initial drop in current to the switch off point.

Technical Information

Glow (or heater) plugs are utilised to aid cold starting, being activated in certain engine conditions. The glow plugs can operate in several ways, the most simple being switched on during cranking or while the ignition is switched on. The glow plugs are wired in series and are fed with battery voltage for a set period of time, which is determined by the 'glow plug timer relay'.

The components soon heat to their operating temperature in a matter of seconds and can seen to glow 'white hot' when tested out of the engine. The plug should heat from the tip backwards, failure to do this means that the plug needs replacing.

Other systems may remain on until the engine's water temperature reaches a predetermined temperature, while others may operate in a similar way but will be pulsed alternatively in sets of two.

The testing of the glow plugs can be achieved in one of two ways, by either leaving the plugs in-situ and monitoring the current draw of them all, or by removing them and analysing their performance visually as they heat up and measuring their individual current draw, at the same time.