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Becb Battery Monitoring System Problem

BECB BMS

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#1 Bassrock

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Posted 29 March 2018 - 07:40 PM

Hi All,

 

Odd bod of a fault, as follows:-

 

So, I have a 2010, 2.0Hdi X7 Estate, which has the BECB module (BOSCH 9664448980) attached to the battery negative terminal.

 

Every so often (mostly in the morning after 5 minutes of driving (every 3 or 4 days or so) I get the battery charge warning along with the dong, dong, dong gong, it then disappears and isn't seen for another 3-4 days.

 

I have a DMM attached at point of failure which tells me alternator is kicking out around 14.2V

 

This started last year (would happen once every so often e.g. every 3 - 6 weeks, but now frequency has increased) and since then, alternator, battery, and BECB have been changed, intermittent fault remains.

 

The BECB was changed by a garage as I gave up trying to fault find (at that time I had no decent diagnostic device). They said the BECB was reporting incorrectly to the BSI, so £200 later fault still the same.

 

So happens, I now have access to a Foxwell NT644, it tells me the battery voltage is 12.2V (reported BECB ECU) but when measured at the battery is 14.2V, so I have a 2V error.

 

But the BSI reports voltage as 14.2V and a secure battery voltage of 12.2V, 

 

Now, where does this 12.2V "secure battery voltage" come from ??????

 

So any ideas ??????????????, think I'm homing in the right direction though !

 

Any help much appreciated.

 

 


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#2 Bassrock

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Posted 07 April 2018 - 05:21 PM

Ok, All, sorted  :D  :D

 

On the battery negative terminal sits the BECB module (battery monitor (this is the PRIMARY source for the "secured battery voltage").

 

On the positive terminal sits a tag with cable assembly bolted to the +Ve supply of the battery and ultimately to the BECB.

 

Disconnect +Ve tag on +ve post, BSI then takes its "secured battery voltage" (compares it with a battery voltage from elsewhere) from ABS/EBS or elsewhere if it cannot see that derived from the BECB.

 

Guess what "secured voltage matches" battery voltage and haven't had a fault intimated for 4 days.

 

All I need to do now is find the root cause fault in the power supply harness.

 

Basically, because the BECB was receiving the wrong/intermittent supply voltage it was telling the BSI incorrect voltage values and the BSI re-acted accordingly, however the BSI voltage was at battery voltage e.g 14.2 volts when charging but

was being comped with the incorrectly generated voltage from the BECB..

 

 

Happy days :D , Oh no whats that noise from the electric steering pump, quick trip to supply guys for some steering fluid and problem solved phew, another near miss.....


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#3 paul.h

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Posted 08 April 2018 - 02:22 PM

Our C4 started to give poor acceleration whilst still under warranty so the Citroen dealer did a diagnostic which found a U code pointing to a fault in the fuse unit fastened to the battery. After fitting a new one it was then ok. Whether that gave a low voltage I do not know since I did not have a diagnostic tool.

 

To drop 2 volts could be a poor connection, a wiring fault or component but possibly not within the bit you already had replaced.