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Part names confusion

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Mon Jan 24 2022, 06:24am
Member No: #55564
Joined: Feb 07 2020
Location: Notts
Please can anyone tell me if the following are one & the same item?
*Voltage Retention Unit
*Battery Protection Management Unit
I have a battery drainage problem with a Grand C4 Picasso 15 reg.
A local "Citroen specialist" replaced the former (VRU) which didn't solve the problem so I've now had it at a "main dealer" who claim it needs the latter (BPMU) replaced. Neither can/will provide part numbers. The main dealer claims there is no way of seeing which part was changed less than 3 months ago (2 of which it has spent sat in their workshop)!
Mon Jan 24 2022, 10:28am

Member No: #82
Joined: Jan 22 2007
Location: Hoylake
AFAIK they are not the same.

The Voltage Retention Unit is part of the Stop/Start system. I believe early Citroen systems used a massive capacitor (>8F) to hold power and then turn the alternator and its linked belt to turn and start to the engine. This system did not use the car's conventional starter motor.

The Battery charge status control unit is very complex but primarily is there to protect the battery and prevent unnecessary discharging.
1 User said Thank You to BigJohnD for this Post :
 she2656 (24 Jan 2022 : 18:20)
Tue Jan 25 2022, 04:30am
Member No: #48843
Joined: Jul 06 2017
Location: Scotland
What voltage is it retaining, even 8F is not enough to hold much in terms of car needs
Tue Jan 25 2022, 08:13am

Member No: #82
Joined: Jan 22 2007
Location: Hoylake
I've no idea, probably 12V to turn the alternator/starter like on a motorbike. The capacitor has a huge capacity, measured in Farads, maybe as much as 150, and a control unit to manage use and charging.

There's loads for sale on EBay. Try part number 9801739380.

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