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A.O.N - Approved Vauxhall Specialist (Anthony)
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Discussion Starter · #1 ·
With winter nearly upon us, it is a good time to ensure that the glow plugs on your Diesel engined vehicle are working properly. Diesel engines can become very difficult to start if two or more of the glow plugs stop working.

Generally, with newer vehicles, you will get an engine management light on and fault code P0380 - Glow Device Circuit General Error if one or more of the plugs are defective.

Older vehicles will just become difficult to start, and produce lots of grey/white smoke (not steam) and misfire badly.

Tools Required

Testing the glow plugs is quite a simple job, the only piece of equipment needed being a multimeter capable of measuring resistance, and the necessary tools to access the glow plug connections.

As this guide could apply to any of the Diesel engines fitted to the Vauxhall range since the early eighties, it would be very time consuming to produce a guide for each one. This guide will focus on the most common Diesel engine currently being discussed on the forum, this being the Z19DTH/J, or 1.9CDTi 16V engine. It is also a happy coincidence that no tools are needed to access and test the glow plugs! :)


1. Remove the plastic 'beauty cover' from the top of the engine - pulling upwards to release the rubber cups from their mountings. If any of the rubber cups stay on the engine, remove them and re-install in the plastic cover 'hooks'.

2. The glow plugs are at the back of the cylinder head, between the common rail and the intake manifold - see arrows.

3. Pull upwards on the connector to disengage it from the glow plug. These can be quite tight.

4. Set your multimeter to the lowest resistance range.

5. Connect the black test lead from the meter to a clean piece of metal on the engine to act as an earth point.

6. Touch the red test probe onto the centre pin of the glow plug (arrowed).

7. The reading on the meter should be approximately 1ohm for a good glow plug. The actual reading will vary according to the temperature of the engine, and the accuracy of the meter, quality of the earth connection etc. Any plug reading 5ohms (or more) is suspect and should be replaced.

8. Repeat the process for the remaining plugs.

Many other engines (current 1.7's, 1.9 8V, and later 2.0DTi's) have separate connectors for each glow plug, so follow the above process but you may need to remove other components for easy access to the glow plugs.

Older Diesel engines (X20DTL/H, X17DTL, Isuzu 17DT & 15DT, 16D) have a metal 'bus bar' connecting all of the plugs together in parallel. This bar must be removed completely before an accurate reading of each plug can be taken.

Removing glow plugs

Here is where the horror stories start! ;)

Modern glow plugs are small in diameter to be able to fit within the very crowded cylinder head. They are also very long compared to their diameter to be able to reach down into the combustion chamber. This means they are not very strong when subject to torsion (twisting) force. Any carbon build up on the combustion chamber end, or corrosion on the screw threads, can mean they will snap rather than unscrew cleanly from the engine.

There are a few things you can do to improve your chance of them coming out in one piece:-

* Apply Plus-gas or other rust release agent (WD-40 is not so good at this as the proper stuff) for as long as you can before attempting to remove the plugs.

* Have the engine at normal operating temperature when attempting removal.

* Use a well-fitting hex socket (6 sided, rather than the usual 12-point bi-hex).

* Use a 1/4" drive ratchet, and use as few extensions as possible. This ensures that too much torque is not applied to the plug (easy to do with larger ratchets), and you are turning the plug rather than applying a turning AND bending force.

Good luck! (Y)

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