Toyota Tundra

Toyota Tundra

2012-2015 Toyota Sequoias and Tundras can be equipped with a flex fuel, E85 capable 5.7L V8, the 3UR-FBE, that is equipped to run on high ethanol content gasoline.  Unfortunately these are prone to hard starts, extended cranking, a rough idle and a check engine light that can result from odd fuel trims.  The most common codes are:

  • P1604 – Startability Malfunction
  • P1605 – Rough Idling
  • P0171 – System Too Lean (Bank 1)
  • P0172 – System Too Lean (Bank 2)
  • P0174 – System Too Rich (Bank 1)
  • P0175 – System Too Rich (Bank 2)

The vehicle’s engine control module measures the amount of ethanol in the gasoline and adjusts the air/fuel mixture ratio on the fly depending on this alcohol measurement.  100% gasoline is mixed at a 14.7/1 air/fuel ratio, while E85 (85% ethanol, 15% gasoline) is mixed at a 9.8/1 air/fuel ratio.  The car adjusts between these two ratios depending on the ethanol content of the fuel (which can range from 0-85%).

The problem lay in the vehicle’s measurement of the alcohol density being incorrect for a cold start – the car runs even more fuel than normal to get a cold engine started, and using the wrong fuel ratio at the outset leads to ever more skewed startup fuel trims, a hard start and rough running.  If the measured Alcohol Density Estimate is greater than 15% and your fuel trims still read negative/lean, there is a repair from Toyota for your truck.

The solution to this is to reprogram the engine’s ECM with an updated calibration to correct the fuel trims as adjusted against the Alcohol Density Estimate, afterward filling the tank with low ethanol gas (E10 or less).  As Eden Prairie and Chanhassen’s Toyota and Lexus repair specialist, CARspec is happy to offer the recalibration to repair the condition, something most general auto mechanics can’t offer due to the toolset needed to upgrade the vehicle’s ECM.

We hope this gets a Toyota owner back on the road with a cleared check engine light and a smoother engine!