OBD Codes P0171 and P0174?

HESCHUTZ

MEMBER
2020 TOYOTA SIENNA
3.5L
6 CYL
2WD
AUTOMATIC
51,000 MILES

The check engine light in our vehicle listed above has been off and on intermittently for the last several weeks. Ran out and grabbed an OBD2 scanner to pull the codes. Each time the light comes on, the codes are consistently showing P0171 and P0174 with P0171 being the primary DTC causing the light to illuminate.

As for symptoms, there is nothing noticeable. No hard idle, no trouble starting, or anything like that. On one occasion about a week ago I noticed while idling that about every 20-25 seconds the engine would gradually go from just over 1,000 RPM up to 2,000 RPM then drop back down and repeat.

I've already checked the air filter which was clean and had been replaced recently. I'm not seeing any loose or worn hoses that are obvious. I'm also not hearing any whistling sounds as a result of a vacuum leak.

Just replaced the O2 sensor for Bank 1 Sensor 2. No noticeable change and the light came back on again.

Separately (or at least I believe it is) we had a problem back in April where the van wouldn't turn over after fueling. The engine would finally start after trying 6-10 times. On the first start it would hit roughly 300 RPMs and then die. On the next start, it would fully turn over and jump up to 1,000 RPMs and then run fine. It would start fine every time afterwards until the next refueling at which point it would start all over again. The tech ultimately decided it was a bad positive terminal cable which was replaced after taking it in to the dealer and paying for the diagnostic on several occasions, plus labor and parts. Needless to say, it just did it again the last two times we've refueled. Gas cap is on tight. The scanner is showing DTCs P0455 and P0441.

Most recent freeze frame report is attached. Anyone have any thoughts?

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1 Reply

KEN L

MASTER CERTIFIED MECHANIC
48,363 POSTS

Hello,

The OBD (On-Board Diagnostics) codes P0171 and P0174 in a 2020 Toyota Sienna are indicating issues related to the fuel system, specifically that the engine is running too lean on both banks of the engine. Here's what each code means:

P0171: System Too Lean (Bank 1)
P0174: System Too Lean (Bank 2)

These codes suggest that the air-to-fuel ratio in the engine is unbalanced, with more air than is ideal for proper combustion. A lean condition occurs when the engine receives too little fuel or too much air.

These codes are associated with low fuel pressure/delivery or the MAF sensor has gone bad and needs to be replaced. The fact that it acts up after fueling is telling me the lift pump (primary pump - in tank) in the tank is going bad. Here is how the job is done to fix the problem. Check out the images (below). Please upload pictures or videos of the problem so we can see what's going on.

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