Glow plugs/pressure sensors

[Spineytoo]

I had "Service Soon" showing over many weeks and thought the computer knew that I needed the oil changing! Seems it is just a fault indicator, and in my case, the error codes read by the garage said, two glow plugs were faulty.  I have been looking for replacements and it seems likely that the correct parts are the combined glow plug and pressure sensor - much more expensive at over £30 compared with £7 for straight glow plugs.

Does anyone know what the computer uses the pressure sensor data for?

Does a faulty pressure sensor also trigger the "Service soon" message?  What would be the consequence of fitting plain glow-plugs?

[Vauxhall Owners Club]

The service lamp shows if there is an engine fault to say you need to visit your local garage.
In the case of the Glow Plugs, they may just be below par and still work effectively but may fail during colder months.

In the case of a Service Soon light, this also could be down to the fact that the oil has degraded or the Oil Quality was not reset in the ECU last time is was serviced and this can flick the lamp on 

[Spineytoo]

Thank you.

I have discovered that the pressure sensor/glow plug is very expensive; obtainable on line for £98; I bought a brand new OEM BERU one from Ebay for £88.75. I have measured the resistance of the 4 glow plugs; 1.2, 4.8, open circuit, 1.2 ohms. So I replaced the open circuit one with the new one, which also showed 1.2 Ohms. The Service vehicle soon message still shows. The non-Vauxhall garage mechanic reported only 2 faults - both glow plugs.  I found an unverified comment online which suggested that the ECU would show the warning if the pressure readings were out of specification as one would hope and expect. I don't know if the ECU OBD reader used by my mechanic would be able to give precise details of the glow plug fault, but it is likely that 4.8 ohms (and the reduced current) would be outside spec. I suppose I should bite the bullet and spend another £88.  But the car starts OK as it is.

BERU says that the use by the ECU of the cylinder pressures allows reduction of NOx and carbon in the exhaust by up to 90%. Very useful if true!

When I owned a Skoda Octavia, I bought the Ross-Tech OBD appliance. What a pity Vauxhall has been so difficult about allowing owners to have their own diagnostic devices.

[Vauxhall Owners Club]

I think I may be tempted to run the car until it does become an issue with starting in the cold weather