Your Mini Cooper's error code 4B90 points to fuel system issues, possibly the high-pressure fuel pump, but it could also involve the low-pressure pump, fuel filter, injectors, or a faulty pressure sensor. Mention the loose battery terminal to the mechanics and ask if they've thoroughly tested these components and checked for fuel contamination or electrical faults. Request a clear diagnosis and repair cost breakdown, and consider a second opinion if the repair is expensive Orange County Toll Road system

Hi all,

so I recently bought a second hand r57 Mini Cooper, drove lovely but suddenly the engine cut out, wait 30 secs then could restart, got home. Drove fine for 4 days then cut out again but no restart…half hour later restarted & got home, called AA they came up with error code 4b90

fuel high pressure monitoring (rail) engine start. 4b90

When he inspected the engine he noticed the positive terminal on the battery was loose so tightened that,  car started for 20 secs then cut and no restart. Live data on fuel system read that fuel pressure was only 11bar but should be 300 on cranking. 

took it to a garage, I told them all this, they’ve had it for three days and all I’ve been told so far is it could be the fuel pump and may cost thousands worst case.

i know nothing about cars but my gut says somethings off or am I wrong.? 
any advice would be appreciated. Especially with what to ask or say to the mechanics. Thank you