2001 C5 2.2HDi -P0380–Over-heated glow plug connector

[aspire_helen]

Recently, I noted from Lexia3 that the Injection ECU history had, at some time, recorded P0380 “Permanent Fault –Pre-post heating relay circuit. Short circuit to positive”. However, I had had no warning on the MFD or dash.
As access to the glow plugs is very difficult, it made sense first to conduct resistance and continuity checks with the plugs in place and connected. The first test was continuity between the +ve terminal strip (#2) and the output from the controller/relay (#4) via connector (#3). Bingo! 900ohms – it should be zero. Moreover, it varied wildly between 900 and 1500ohms when I waggled the connector indicating a poor connection or broken wire.
The connector looked OK from the outside, but proved difficult to separate. The photos show why. Inside, the single spade terminal had over-heated, distorting and melting the internal plastic, which was extremely brittle indicating high heat over a long period. There was no corrosion, but oxidation of the metal had reduced the conductivity. Having broken out the metal terminals from the plastic shells, I discovered that the two terminals were a loose fit, the likely cause of the over-heating. I tightened them up for a quick fix, and cleared the fault on Lexia - success.
A permanent repair of the connector would require significant dismantling to remove the +ve terminal strip from every glow plug. However, a much easier fix, with no dismantling, was to run a supplementary cable in parallel to the original glow plug lead. One end has an M5 ring terminal and doubles up on the M5/8mm output of the controller/relay. However, the other end has an M4 ring terminal and attaches under the M4/7mm nut of the farthest glow plug (cambelt end). That end glow plug is the only one that can be reached without any dismantling (not even removal of the engine top covers), working by feel with the assistance of a mirror.

[aspire_helen]

Just an addendum.
1. My early 2.2HDi DW12TED4 has a single metal strip spanning all 4 plug terminals. Later fits have individual leads, making individual plug resistance testing easier (well, a little easier perhaps!).
2. Only the cambelt end glow plug can be accessed behind the cylinder head, albeit blindly. The other 3 are completely obscured by the EGR/heat exchanger/air hoses.
3. I measured the total resistance of all 4 glow plugs in situ at 0.6ohm, which equates to an average individual resistance of 2.4ohms (parallel resistors rule). Happy with that.