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When a normal diagnostic procedure becomes a massive headache

Saturday, December 1, 2018 - 09:00
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The vehicle that caused this is a 2011 BMW X3 2.8i (F25 Chassis) with a 3.0L (N52T) turbocharged engine. It was towed into the shop for stalling while driving and would not restart. I did not physically look at this vehicle on its original diagnosis but did offer the tech assigned to it some direction to find the problem. However, I was asked to get more involved and assist with the diagnosis when a problem still existed after the original repair.

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2011 BMW X3 (F25) with an inline 6 cylinder 3.0L (N52) engine

The vehicle was initially dropped off with the concern that while driving, the engine sputtered and stalled. The engine cranked over fine but would not restart. Once at the shop the technician put the vehicle on a set of GoJaks Car Dollies to get it inside. Normally a couple of people would have just pushed the vehicle inside so they don’t have to work out in the 115 degree Las Vegas summer heat, but this vehicle, like many other modern BMWs, is not allowed to be shifted into neutral if the engine is not running making it very difficult to move.

No fuel or no fuel pressure?

Once inside the shop the technician did his basic checks and decided that fuel was the cause of the crank no start. He stated that he had no fuel pressure with the engine cranking. I asked, “Is there fuel in the tank?” to which he informed me that there had to be since the fuel gauge was reading at half a tank. Based on my experience, and probably anyone who has dropped a gas tank to replace a fuel pump only to find the tank completely empty, I recommended that he add a couple of gallons of gasoline before condemning the fuel pump just to be on the safe side. He did and the engine started within a couple seconds of cranking. 

Using the test plan in the factory scan tool gave me information on how the fuel level sensor circuit functioned. Most importantly, it contradicted what the dealer had stated and verified the vehicle does in fact have two fuel level sensors.

So the fuel pump was working but the fuel level was not being read correctly. The fuel gauge still read at half a tank, which cannot be correct for only having a couple of gallons of fuel in the tank. He came back to me later after some further diagnostic work and said that he had ordered the fuel pump assembly that came with the fuel level sensor. Well, OK running the pump with no fuel didn’t do it any favors so I agreed with his conclusion. On a side note, I later found out that the fuel level sender is available separately without purchasing an entire fuel pump. The dealer did tell the tech that the fuel level sensor was part of the pump assembly when ordered.

New part, same problem

The new fuel pump assembly was installed and the technician noticed that the fuel gauge still read a little under half a tank. He then added more fuel to the tank and test drove the vehicle. The needle still remained at almost the halfway point. A call to the dealer parts department was made and the parts person stated that this model only has one fuel level sensor on the right side and no left side fuel level sender was listed. He stated he also checked for TSBs and any matches in Identifix but came up empty handed.

The code pointed to the right fuel level sensor being shorted to battery positive, however that sensor was already replaced with an OE unit.

At this point the tech had hit a wall since he replaced the only part responsible to indicate the fuel level in his mind, but the same problem remained. Frustrated and out of ideas he asked to have me assist with the diagnosis.

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