Warning low battery voltage

[GREYWACKE]

I am new to the forum but you have previously given me, by reading various threads, amazing technically insightful for which I am most grateful. I wonder if you might assist with my car’s current problem?

Car: Citroen C4 Grand Picasso 1.6 Diesel 115 6 speed manual with stop start function. First registered 22/05/2015 VIN VF7**************[VIN obfuscated, can be read by forum staff]. Logbook gives version 3A9HC8 and adds VTR E-HDI

The problem is a service warning and ‘stop start’ light not going off on starting and occasional Red STOP light when driving ‘Battery Voltage Low’ (most recently with air con on). This first started because the + terminal became disconnected on the motorway. So we stopped at the next safe spot - but the car would not start (flat battery). In short, this was midnight and after the recovery folks trying to jump start several times without success, we were recovered. I replaced the battery (as after 9 years it was at or near its useful lifespan) with what the motor factor said was the correct one (bearing in mind the stop start requirement) and thus AGM. After a while the ‘system’ seemed to reset itself - However, this did not solve all of the problem. I took it to a local garage who established the following codes U1133, U1134 and U1400.

I might add that before the incident on the motorway the warning lights we now get on starting, had shown not shown before - thus I have assumed they are connected events rather than timing coincidence of disconnected events. The mechanic was uncertain as whether there is something wrong with the alternator or if the car simply ‘thinks’ there is something wrong (and thus how then to correct it) or, indeed, the possibility of an intermittent fault. The battery is reading 12.5V (engine off) and. 14.16V engine on at idle speed - it doesn’t seem to go down when drawing electrical power by putting lights, wipers etc on. I attach the alternator details

Alternator

I wonder if the forum has come across this problem and advise on the best cause of action- many thanks for your help.

[GiveMeABreak]

Several issues:

You have the older Stop Start system that has a network voltage maintaining device, and accumulator capacitor hidden away under the front left wing. So although your vehicle battery was well overdue for changing (anything over 5 years is generally at service life end), there is the possibility of issues with this part of system too.

...and as you can from the fault codes the reversible alternator is listed as a culprit in all 3 cases. If the reversible alternator (a special type for some types of Stop Start systems) is faulty it won't be charging either the car battery or the energy accumulator (capacitor) of the stop start system.

So needs further investigation, but as it stands the LIN (Local Interconnect Network) is one of the data networks that the ECUs all talk together on and it would appear that the alternator is not communicating on the network.

You may want to let Citroen deal with it as they should have the technical knowledge to deal with these - but I suspect it may need the reversible alternator that's giving out as it's over 9 years old.

Fault Code:	U1133
Description of Fault:	LIN: The reversible alternator is confirmed absent. Faults in communication between ECUs on the LIN.
Conditions for Fault to clear:	Ignition switched on
Downgrade Modes whilst Fault is active:	Automatic restarting impossible following stopping of the engine (Requires restarting of the engine using the key)
Symptoms:	Problem with automatic restarting of the internal combustion engine Absence of automatic stopping of the internal combustion engine
Suspect Areas:	Supply of the voltage retention device Reversible alternator supply Electrical harness

Fault Code:	U1134
Description of Fault:	LIN: Voltage retention device confirmed absent. Faults in communication between ECUs on the LIN.
Conditions for Fault to clear:	Ignition switched on
Downgrade Modes whilst Fault is active:	Automatic restarting impossible following stopping of the engine (Requires restarting of the engine using the ignition key). Switching on of the warning lamp and/or warning message: "SERVICE" warning lamp.
Symptoms:	Problem with automatic restarting of the internal combustion engine Absence of automatic stopping of the internal combustion engine Malfunction of the Stop and Start switch or its LED
Suspect Areas:	Supply of the voltage retention device Reversible alternator supply Electrical harness

Fault Code:	U1400
Description of Fault:	Alternator LIN network: Registering of a fault on the LIN network. Faults in communication between ECUs on the LIN. Conditions of activation of the diagnostics: At least one of the following conditions must be fulfilled: - Ignition switched on - Engine running
Conditions for Fault to clear:	Driving for 5 minutes
Downgrade Modes whilst Fault is active:	Automatic restarting impossible following stopping of the engine (Requires restarting of the engine using the ignition key). Switching on of the warning lamp and/or warning message: "SERVICE" warning lamp.
Symptoms:	Jerking/stalling Starting problem Lack of power No automatic stopping of the internal combustion engine (Vehicle equipped with "stop and start") Problem with automatic restarting of the internal combustion engine (Vehicle equipped with "stop and start") Malfunction of the Stop and Start switch or its LED (Vehicle equipped with "stop and start")
Suspect Areas:	Engine ECU LIN Alternator

[GREYWACKE]

I would just like to thank you with gratitude for your assistance and the time and trouble in looking into this and drafting your detailed response. If I may, I will revert once I have got to the bottom of the issue. I find the forum invaluable and would like to help others - as there is going to be someone, somewhere with the exact same problem and sitting there like me not really knowing what to do next. Again, many thanks.

[GREYWACKE]

I undertook to update on my issue. Following the original post a GiveMeABreak’s very kind and expert advice I took the car to an auto electrician for a report which, in short, said exactly same as GiveMeABreak’s script above. The alternator was suspected in some form of semi-failure although giving good voltage. As the replacement was quoted at the £2k mark I simply drove it around with the warning light on - yes, somewhat avoiding the decision. Although, somewhat nervous of a failure, I undertook increasingly long journeys basically simply living with the light on and the alarm sounding on starting. Then in October when the clocks went back we were driving along and ask my wife to reset the clock - 10 or so minutes later I noticed the warning light disappeared and 6 weeks later it has not reappeared. It could be completely coincidental the reset of the clock and the warning light disappearing. I can’t say that the fault has gone - simply the warning light no longer comes on. The fault might still bite me in the future and thus very cautious of even hinting at ‘problem solved’ as it could be ‘problem hiding’. I have no idea why this has happened, but hope this update is helpful.