How to Read Fuel Trim?

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Reading Fuel Trim:

The fuel trim value is read by plugging a scan tool into the OBD II diagnostic connector located under the electrical device (on the driver’s side near the steering column). When the secret is turned on, the scan tool will initialize and begin to speak with the vehicle’s onboard computer. Betting on the tool and also the vehicle, it should be necessary to enter the vehicle year, make, model, and engine VIN code before the scan tool can read the info.

The engine must be started and running to read the fuel trim information. Betting on the scan tool and the way its menu options are founded, you decide on the choice that enables you to read system live data. This can display a protracted list of sensor outputs and other readings called PIDs (Parameter IDs). On this list are going to be two fuel trim values for inline-four and six-cylinder engines, and 4 fuel trim values for V6 and V8 engines (one pair for every cylinder bank).


There are two styles of fuel trim values shown:

Short Term Fuel Trim (STFT) is what the engine computer is doing to the fuel mixture without delay.

This value changes rapidly and might bounce around quite a bit looking at engine load, speed, temperature, and other operating conditions).

Values normally range from negative 10 percent to positive 10 percent, though the readings may jump the maximum amount as 25 percent or more in either direction.

Long Term Fuel Trim (LTFT) may be a future average of what the engine computer has been doing to balance the fuel mixture over a predetermined interval of your time.

This value could be a more accurate indicator of how the fuel mixture is being corrected to catch up on changes within the air/fuel ratio that are occurring inside the engine.

  1. STFT B1 is brief Term Fuel Trim engine cylinder Bank 1
  2. STFT B2 is brief Term Fuel Trim engine cylinder Bank 2
  3. LTFT B1 is future Fuel Trim engine cylinder Bank 1
  4. LTFT B2 is a long-run Fuel Trim engine cylinder Bank 2

How does one know which cylinder bank is 1 or 2 on a V6 or V8 engine? Bank 1 is the cylinder bank that has cylinder favorite within the engine firing order.

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