Citroen Relay 2017 diesel not charging

[dpround]

I am not exactly certain which engine is fitted. It has addblue and apparently is a PSA engine, not the Transit engine in earlier versions of the van. I am guessing a 2.0HDI. The factors web pages agree from the registration.

The van is not charging the battery, but thinks that it is as the battery warning light lights when switched on and goes out when the engine is running. Voltage both at the battery and alternator terminals remains around 11.5V, so definitely not charging. The alternator has one power wire and two low current wires. One has 12V with the ignition on. I would be certain that it was the alternator was faulty normally, but there are other random faults reported due to the ECU 5V rail for sensors being low, like low oil pressure when there is really slightly excessive pressure when measured with a physical gauge.

Is there any chance that the alternator fault is caused by ECU issues? My guess is that the alternator is largely autonomous, but I am not very familiar with these later euro 5/6 engines. Folk wisdom suggests that the alternator fault might cause strange effects with the ECUs. The voltage is still in spec at 11.5V so it shouldn't, but perhaps reality is different.

Many thanks for any tips. The alternator is expensive at £250 - £350 so don't really want to get this wrong. ebay has 150A alternators at £150, but the factors all suggest a 220A alternator. Thoughts?

Thanks in advance.

[dpround]

I should have said that all the faults appeared to happen at the same time - on the way to MOT after standing for a while...! To my mind this suggests there is a single fault that is causing all the symptoms.

Where is the engine earth strap? It appears to be working, but I would normally check it for these symptoms.

[GiveMeABreak]

Is there any chance that the alternator fault is caused by ECU issues?
Thanks in advance.

It's more likely to be the other way around - as in a weak car battery will cause sensor and ECU problems if the voltage is too low. As you already know the battery isn't being charged when running, then you either have a duff battery or the charging circuit / alternator is likely at fault. Start here before dealing with sensors.

[dpround]

Well, replacing the alternator fixed the charging issue only. The 5V bus remains faulty. I guess I have multiple faults to find At least the alternator worked as it should.

[dpround]

For future reference, even though it is a two pin plug on the low power wire, there is only one pin used so very little scope for extra complications. No CAN bus control, which is what I was worried about.

[GiveMeABreak]

Really needs a proper diagnostic, but this being a Ford engine it will likely need the S1279 module if using Diagbox and a Lexia kit, otherwise a different diagnostic tool. If you get any codes, put them up here with the VIN.

[dpround]

It is a PSA engine in this van as far as I can figure out. definitely not the Transit engine in earlier versions.

The local garage identified the 5V reference bus voltage low at around 3V which is affecting multiple sensors. I will repeat their work, but have no reason to doubt them. I am not keen on their recommended course of action which was to replace the ECU set. Even if a 5V regulator is bust in an ECU, it can't be that hard to fix surely?

[GiveMeABreak]

Yes, sorry - don't know where I got the Ford Puma reference from - must of been dealing with another issue on the Forum! Most of the ECUs are sealed - but you may be able to speak to an ECU repair specialist for advice and send it off for repair if you're sure the correct supply voltage is getting to the ECU itself.

[dpround]

Fault found with the sensors number 2 5V supply P2669-01. Unplugging the engine side plug from the ECU cleared the 5V fault, though of course caused many new codes. This confirmed that the fault was on the engine loom or sensors, not in the ECU. A random website suggested the thermostat motorised housing as a likely culprit. Plugging the engine back into the ECU and disconnecting just this housing confirmed this. The only downside is these motorised thermostats are expensive!

[GiveMeABreak]

.... but probably cheaper than an engine ECU and all the requisite coding required! Glad you found the culprit.