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Old 08-03-18, 08:43 PM   #1
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Default Fuel gauge reading drops to zero when engine starts

This is a 2011 Boxer based campervan (Autocruise) with very low mileage. It runs well but has an irritating problem.

With the ignition on the fuel gauge reads correctly. When the engine starts the reading drops to zero. The cruise control cannot be engaged. All other instrument panel functions are good except fuel related computer readings.

Diagnostics show no relevant faults. The BSI contains the correct fuel value, the instrument panel also contains the correct value when the ignition is on but zero as soon as the engine starts.

I have had the instrument panel checked by a specialist and no fault was found. Another instrument panel behaved in the same way which suggests the fault is in the van.

The fault came on gradually. Initially after running for an hour, then half hour etc until it is present whenever the engine starts. In the early stages it seemed to clear when the vehicle went downhill on the overrun.

There are a couple of threads on this forum which could be related, but no solutions. I have also found a reference to the problem on a motorhome forum, but no solution. Recently I found another similar vehicle of the same age with very similar symptoms, so it cannot be that unusual.

So far this fault has baffled everybody who has seen it. Any suggestions where to look next would be much appreciated.
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Old 09-03-18, 09:14 AM   #2
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Does the brightness of the dash change when engine is running compared to just ignition on?
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Old 09-03-18, 01:21 PM   #3
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No, I have not noticed anything like that. I have checked the supply voltage at F37 (brake switch, third stop lamp, instrument panel): 12.3V with ignition on, 14.4V with engine running.
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Old 02-04-18, 09:25 PM   #4
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I have now come across a couple more vehicles of the same year with these symptoms. Please could someone give me a critical appraisal of my theory set out below:

When the ignition is turned on the BSI interrogates the fuel level sensor and puts a message on CANB with the correct fuel value. The instrument panel responds correctly. The BSI and instrument panel both contain the same, correct fuel value (confirmed by diagnostics).

When the engine starts "some device" broadcasts the "fuel zero" message on CANB, the instrument panel interprets this message and stores zero in its fuel register. It must be a genuine message with a correct checksum (rather than noise or some other message which has been corrupted) because the instrument panel responds to it. At this stage the BSI has the correct fuel reading but the instrument panel zero (confirmed by diagnostics). Subsequently the instrument panel tries to compute the fuel value by subtracting the fuel used, as measured by the EMU, until the engine is stopped. It cannot, so the value remains at zero. The tank sensor only seems to be interrogated when the ignition is switched on, but there may be other trigger events which I have not found. (I have emptied the tank of a previous Peugeot through the injection system and the gauge shows full until the engine is turned off.) The zero fuel measurement inhibits cruise control functions and messes up fuel related readings on the trip computer, all done within the instrument panel.

The BSI retains the correct fuel reading, so it seems unlikely the BSI hardware would be the culprit, but there could be something strange is going on in its software.

This is where my speculation ends! I have seen references to the "zero fuel" reading in other posts. One was cured by replacing the radio (I have removed mine to check), and several are either unresolved or gone away.

Comments or better ideas would be appreciated.
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