Disco 4 running for 1 minute only

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Pborrell

New Member
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6
Hi
My discovery 4 only runs for a minute and then cuts out. Restarts fine. However when running every 5 seconds it does a little judder!

The garage has drained the tank to make sure only diesel in and then replaced the fuel filter. Still doing the same thing

Any ideas on what it could be or what we do next?
 
That sounds very much like 'driver inducement' for low fuel level - what is the gauge showing? do you have any ability to read fault codes & live values for the engine and the body control module?
 
Graculus said:
That sounds very much like 'driver inducement' for low fuel level - what is the gauge showing? do you have any ability to read fault codes & live values for the engine and the body control module?
Click to expand...
No I don’t. The fuel gauge shows no fuel. It stopped working a 3 weeks ago it just says no fuel even when I know it’s full. I’ve filled up at least 5 times since. Is there something that protects the engine by switching it off then?
 
Yes, it's coded into the BCM to signal the engine control module to force a misfire then shutdown, it's likely the calculated level has dropped below the 'safe' level - there are two in-tank sensors, possibly one has failed or come adrift.
The reason for the shutdown is to protect the HP fuel pump which will self-destruct (and take the fuel injectors with it) if allowed to run dry.

Fix the tank level indicator issue and the engine will sort itself.
 
Wow thank you for that diagnosis!

The only thing I don’t understand is why it worked so well for so long with a zero reading. It suddenly went wrong 2-3km after topping up the tank
 
There are two sensors due to the shape of the tank, although both are separately connected, the signals are averaged to give a calculated fuel volume remaining, the IPK calculates the fuel usage and adjusts the remaining distance available, once this is calculated as 'zero' regardless of the reported fuel level, the BCM will signal to the ECM to implement 'driver inducement'. There is a much more in-depth description in the workshop manual but that's a basic summary.
In terms of diagnosis, It'd be worth checking the wiring to the tank hasn't been damaged by rodents or friction before removing the tank to further diagnose the level sensors. Clearly there is a connection to the primary LP fuel pump, either the level sensors, wiring or the BCM itself are defective. It may be worth trying a battery disconnect / wait 10 mins / reconnect before getting too invasive.
 
My car is in a garage in France and they have done this and it works!! They can’t believe it! Can I ask why disconnecting the battery works??
 
Pborrell said:
My car is in a garage in France and they have done this and it works!! They can’t believe it! Can I ask why disconnecting the battery works??
Click to expand...
Means that they know nthing about D4s(or other CAN-bus vehicles)... and even if it works after the "hard reset" as long as the gauge reading is not restored it will end up on the same default in short time
 
sierrafery said:
... and even if it works after the "hard reset" as long as the gauge reading is not restored it will end up on the same default in short time
Click to expand...
Exactly this, unless the cause of the incorrect fuel reading is resolved, you'll be back in the same situation. If it has resolved the fuel gauge readings, then get the starter battery tested, it may not be holding sufficient charge to prevent voltage dropping excessively low during cranking and causing the BCM to 'forget' things...
 
so how long will it revert back if the guage problem isn't fixed?- can I get it home (approx 1000km) and then fix it or should I try and get the french garage to fix?
 
I’ve got it back to the uk! Fuel usage stuck on zero but It ran beautifully for 400km and then did the same thing so I stopped and disconnected the battery for 10 minutes and finished the journey home.

I’ve spoken to 2 garages and neither have heard of “driver inducement” so not confident they will be able to fix it. Any recommendations in the north Cambridgeshire area?
 
All they need to do is sort out the fuel measurement - the 'driver inducement' is in the software of the ECM and not the source of the issue.
 
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