The impellers inside of Denso branded fuel pumps may have been excessively exposed to a drying agent during manufacturing. This leads to them cracking, absorbing fuel, and deforming so badly that they stop sending fuel to the engine. Subaru has issued a recall for the problem but some say it doesn't go far enough.
Denso's low pressure-fuel pumps, which can be found in certain Subaru vehicles, are failing because of an internal defect.
Fuel pumps manage the flow of gas from the tank to the engine. But Denso's pumps use low-density impellers that can crack, absorb fuel, and deform to the point that they interfere with that flow.
Without a reliable stream of fuel, it's only a matter of time before the engine runs rough, becomes difficult to start, or stalls out in the middle of the road.
The Impeller Problem
Fuel pumps are a critical component in the vehicle's fuel injection system. Subaru uses two – a low-pressure pump in the gas tank, and a high-pressure pump further up the line.
The low-pressure pump uses a rotating plastic disk, known as an impeller, to draw fuel from the tank and impel it up the line towards the high-pressure pump. If the impeller can't rotate properly, which is often the case with these Denso pumps, it won't be able to draw fuel.
Once the low-pressure fuel pump stops reliabily moving gas, it hurts multiple components further "downstream."
The high-pressure fuel pump won't have enough lubrication and can overheat.
The engine will eventually run rough, and the excess shaking causes premature wear on the rubber mounts for the engine and drivetrain.
The shaking can also damage materials in the catalytic converter.
Subaru says they received 32 complaints about the low-pressure fuel pumps between July 2019 and January 2020. Of those complaints, 75% indicated the engine wouldn't start, while the other 25% said the engines lost power while driving at low speeds.
Subaru engineers collected the failed parts and found cracked and deformed impellers that couldn't spin because they interfered with the pump body itself.
The internal investigation concluded that the low density impellers were exposed to a drying solvent for a long period during manufacturing. This over-drying creates fine cracks that slowly expand as they absorb fuel.
Engineers narrowed the manufacturing dates of affected vehicles down to anything built between April and July of 2018, but that date has been disputed.
Subaru Recalls Over 200,00 Vehicles
Recall #WRD-20 was announced back in April of 2020. Subaru offered to replace the low-density impellers with higher density impellers that aren't as prone to cracking.
The list of affected vehicles included:
Using their engineer's advice, the recall was limited to vehicles built between April and July of 2018.
Canadian lawsuits believes owners need more information
A couple of Canadian lawsuits don't believe the recall goes far enough in making sure owners aware of the potential dangers, and in holding Denso and the automakers accountable.
Denso is accused of knowing about the problem since 2015. Meanwhile automakers will have a hard time saying they were unaware of the issues considering the wide-range of owner complaints and warranty submissions.
Yet for some reason, the pumps continued to get installed and the recall wasn't issued until 2020.
Not only were owners put in unneccessary danger for those five years, they also experienced dimished resale values and out-of-pocket costs for diagnosis and quick fixes for rough-running engines.
Even now, owners aren't being made aware of the dangers the defective fuel-pump poses until it gets replaced in the recall.
USA lawsuit says the recall doesn't cover enough vehicles
While the recall focused exclusively on 2019 models, the lawsuit believes the pumps can be found in vehicles going back to the 2013 model year. Additionally, it wonders why certain 2019 models, such as the Forester, weren't included.
The suit, Adnan, et al., v. Subaru Corporation, et al., believes there are an additional 188,000 owners at risk of suddenly stalling out and thinks Subaru should expand their recall or at least notify owners of potential problems.
Quick Notes About this Problem
The higher density switch. Denso did not start using a filter with a higher density impeller until July 2019. Presumably that is what will be used in the recall.