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I found the following error in the error log of my Ford Focus Tunier 1.6 tcdi diesel 109HP (2006):

P0380 OBD-II Trouble Code: Glow Plug/Heater Circuit “A”

First i thought it was due to a defect glow plug - as the error message indicates.

I then messured all glow plugs based on this answer by touching one end of a ohm meter to the end of the glowplug and one on the engine. All glow plugs had the same resistance.

The car still drives but it is in limp mode. This means that the rpm and the acceleration of the car is limited (~3000rpm).

Based on the resistance measuring i assume that the glow plug isn't the reason for that error.

What else could be the cause of this error? (And how to fix it?)

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    I would not trust an ohms test, the PCM is seeing a real issue with the heater circuit in the glow plug. Only other thing I can think of is a short to ground in the heater circuit to that glow plug somewhere in the wiring harness. Replace the glow plug to rule it out, then look for more complicated problems. – Moab Jul 17 '18 at 16:31
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    @Moab: Good Answer! A pity we can´t vote for it ... – Daniel Jul 19 '18 at 10:31
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Check if there is voltage coming to the plug when you turn the key into ignition. Keep in mind that "glow plug heating" indicator on your dashboard does NOT reflect the actual state of glow plug being powered on or not. Indicator is just a warning that you should wait few more seconds before trying to start the engine.

AFAIR Ford 1.6 TDCI engine enters emergency mode when all 4 glow plugs are burnt. So they might have the same resistance because they are all faulty. If they were not replaced previously, you should probably try to change them anyway.

But beware that they are quite brittle and after many years they tend to stuck. Be very cautious because if the glow plug breaks, parts of it might fall into the cyllinder and if not removed properly, these parts could damage your engine or anything on the way out (valves, turbo etc.)

  • Thank you for your respond! Im going to it. I also thought about just changing them so i can be sure, that it's another problem but i was scared of ruining the hole engine (Just as your warning indicates). – Yannjoel Jul 18 '18 at 8:06

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