Error code 5 relates to a pair of resistors on the side of the injection pump, at least on the 2.4TD engine.

These resistors are installed when the pump is calibrated and fine tune the timing and fuelling.

I measured both resistors. The grey one was 0.622kΩ while the beige one was open circuit. The insides are potted in epoxy, so I dug out the trusty Dremel and went in.

You can see a pair of solder tabs sticking up - the original resistor, which I ground away, was soldered on here. Judging from the resistor body, it was no more than a standard 0.25W resistor.

The problem now was knowing what value the resistor was originally.

I managed to find a scan of the manual for the Denso injector pump. I’ve also converted it into a pdf.

From that, I was able to work out the resistance value from the part numbers. Here’s a list linking to the resistors which are available from Farnell. First, the grey one.

Code Resistance
001 0.243kΩ
002 0.267kΩ
003 0.294kΩ
004 0.316kΩ
005 0.348kΩ
006 0.384kΩ
007 0.412kΩ
008 0.453kΩ
009 0.487kΩ
010 0.523kΩ
011 0.576kΩ
012 0.619kΩ
013 0.681kΩ
014 0.732kΩ
015 0.787kΩ
016 0.866kΩ
017 0.931kΩ
018 1.020kΩ
019 1.100kΩ
020 1.210kΩ
021 1.330kΩ
022 1.430kΩ
023 0.068kΩ
025 0.100kΩ
026 0.121kΩ
027 0.133kΩ
028 0.154kΩ
029 0.174kΩ
030 0.196kΩ
031 0.221kΩ

Now the beige one.

Code Resistance
001 0.154kΩ
002 0.174kΩ
003 0.196kΩ
004 0.221kΩ
005 0.243kΩ
006 0.267kΩ
007 0.294kΩ
008 0.316kΩ
009 0.348kΩ
010 0.383kΩ
011 0.412kΩ
012 0.453kΩ
013 0.487kΩ
014 0.523kΩ
015 0.576kΩ
016 0.619kΩ
017 0.681kΩ
018 0.732kΩ
019 0.782kΩ
020 0.866kΩ
021 0.931kΩ
022 1.020kΩ
023 1.100kΩ
024 1.210kΩ
025 1.330kΩ
026 1.430kΩ
027 1.580kΩ
028 1.780kΩ
029 1.960kΩ
030 2.210kΩ
031 2.490kΩ

Solder the appropriate resistors in.

Now they need sealing from the elements. Check they read ok on a multimeter first though! After a good clean in some isopropyl alcohol, I used some Sugru to seal them up.

Instead of Sugru, you could use some proper potting compound or even some mastic, but ONLY neutral cure mastic. If the mastic smells of vinegar, don’t use it! The acetic acid released as it cures will eat into the resistor wires.

After all that, I reset the ECU and the code 5 had been eliminated.