Capperdog said:

Hi Folks,
Had the car for 9 months now and enjoyed most of it. As with all 13 year old's it has needed a few things but managing to do most myself, new alternator being the most "fun" so far...
During a very cold February the fuel gauge dropped to zero and low fuel warning etc. There were no performance issues or cut-outs on the many miles and motorway driving I constantly do. For about 10 days the fault was intermittent then went away for a couple of months before now being full time on zero.
I have lifted the rear seats and carpet to check on wiring, all look ok. Next I have lifted the cover plate and checked the wiring and plug/socket there and again all look good.

Just before I open up the top of the fuel tank I thought I'd try jumping the fuel gauge feeds etc. By checking the wiring diagrams around I believe the layout is:

pin 1 = white with red stripe, from instrument cluster to sender unit (both)
pin 2 = black with pink stripe, from sender unit 1 to instrument cluster
Pin 3 = white with blue stripe (thick heavy duty), fuel pump module to pump
Pin 4 = black (thick heavy duty), fuel pump module to pump
Pin 5 = white with blue stripe, instrument cluster to fuel pump
pin 6 = black with pink stripe, from sender unit 2 to instrument cluster

So if that's correct I should be able jump pin 1 to pin 2 and possibly pin 6 to get a reading on the fuel gauge??? Anyone with better ideas?

Don't want try it without giving a chance for someone to say "stop, you numpty..."

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• pin 1 = BK 0.75D (black with pink stripe), -‘ve return from both active & passive sender units to instrument cluster (see note below)
• pin 2 = WU 0.75D (white with blue stripe), +’ve feed from instrument cluster to active sender unit
• pin 3 = B 2.5D (black, thick heavy duty), -’ve fuel pump module to fuel pump
• pin 4 = WU 2.5D (white with blue stripe, thick heavy duty), +‘ve fuel pump module to fuel pump
• pin 5 = BK 0.75D (black with pink stripe), -‘ve from fuel pump earth to fuel pump module and ground (see note below)
• pin 6 = WR 0.75D (white with red stripe), +’ve feed from instrument cluster to passive sender unit

Capperdog said:

Thank you MarJon,

That info is very useful. I can see I have made a fundamental (numpty!) error in numbering the pins in reverse order by looking at the plug, not the socket…

The corrected actual sequence on my L322 MY2010 is:

• pin 1 = BK 0.75D (black with pink stripe), -‘ve return from both active & passive sender units to instrument cluster (see note below)
• pin 2 = WU 0.75D (white with blue stripe), +’ve feed from instrument cluster to active sender unit
• pin 3 = B 2.5D (black, thick heavy duty), -’ve fuel pump module to fuel pump
• pin 4 = WU 2.5D (white with blue stripe, thick heavy duty), +‘ve fuel pump module to fuel pump
• pin 5 = BK 0.75D (black with pink stripe), -‘ve from fuel pump earth to fuel pump module and ground (see note below)
• pin 6 = WR 0.75D (white with red stripe), +’ve feed from instrument cluster to passive sender unit

NOTE: pins 1 & 5 have their BK wires join with a 3rd BK wire which then enters the loom just inboard of the top body cover and rubber seal. The single crimped connection looks original and is shown in the second attached photo.

Going from this I believe there should be positive non-PWM feeds from both pin 2 and pin 6 because they should feed their respective sender units which are magnetic linked resistance type “potentiometer” sender units. When I measure this, both pins show 0.98 dc volts which seems a little low. Does anyone know what this should be?

I am wondering if I have an fault with the instrument cluster or the wiring from it to the sender units.

View attachment 295100View attachment 295101

Click to expand...

Capperdog said:

Thank you MarJon,

That info is very useful. I can see I have made a fundamental (numpty!) error in numbering the pins in reverse order by looking at the plug, not the socket…

The corrected actual sequence on my L322 MY2010 is:

• pin 1 = BK 0.75D (black with pink stripe), -‘ve return from both active & passive sender units to instrument cluster (see note below)
• pin 2 = WU 0.75D (white with blue stripe), +’ve feed from instrument cluster to active sender unit
• pin 3 = B 2.5D (black, thick heavy duty), -’ve fuel pump module to fuel pump
• pin 4 = WU 2.5D (white with blue stripe, thick heavy duty), +‘ve fuel pump module to fuel pump
• pin 5 = BK 0.75D (black with pink stripe), -‘ve from fuel pump earth to fuel pump module and ground (see note below)
• pin 6 = WR 0.75D (white with red stripe), +’ve feed from instrument cluster to passive sender unit

NOTE: pins 1 & 5 have their BK wires join with a 3rd BK wire which then enters the loom just inboard of the top body cover and rubber seal. The single crimped connection looks original and is shown in the second attached photo.

Going from this I believe there should be positive non-PWM feeds from both pin 2 and pin 6 because they should feed their respective sender units which are magnetic linked resistance type “potentiometer” sender units. When I measure this, both pins show 0.98 dc volts which seems a little low. Does anyone know what this should be?

I am wondering if I have an fault with the instrument cluster or the wiring from it to the sender units.

View attachment 295100View attachment 295101

Click to expand...

Datatek said:

The sender units may well be full of electronics.

Click to expand...

Capperdog said:

Thanks Datatek, I will be careful. I see you're based in Poitiers, a place I've known well for the past 60 years. My French Godmother lived in a small village called Quinçay, just outside the city passed the airport

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marjon said:

Ok great to be of help, but which wiring dia works for you?

One of the docs showed a resistance test for the level sensors not voltage, are pins 2 & 6 going to the "electrickery" in the CJB or the fuel module thing?

They don't all work on 12v which is why its been said be careful how and what you do.

Your fault could be in the CAN network signal as that's what controls the gauge, from what I can see.

J

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