fault P2669-01 = number 2 5v sensors supply

[dpround]

I believe this will be solved, but want to write this up as it may help someone else. The fault was on a Citroen Relay (Jumper) 2017 2.0Hdi. The fault manifested as an "Insufficient oil pressure" warning on the dashboard and many more fault codes on the ECU. The key fault was P2669-01, which is that the number 2 5v sensor supply is faulty. The lack of this 5V rail caused many other sensor faults. The garage working on the van recommended replacing all the ECUs. That sounded expensive, so I took the van home to see what I could do. Mostly I did a lot of faffing with the oil pressure sensor, which had nothing to do with the problem and was in no way faulty. Finally I managed some more sensible diagnostics. First, disconnect the engine loom from the ECU, handily the ECU connections are broken into two plugs, engine and the rest, so this was easy. This cleared the 5V fault and so indicated the fault was either on the engine loom or was in a sensor. A big of googling suggested that the motorised thermostat housing might be a candidate. Disconnecting this and reconnecting the ECU confirmed this. The only downside is the motorised thermostat housing is also expensive