Is negative fuel trim rich or lean?
If the displayed fuel trim value is a negative number, it means that the ECU is decreasing the injector pulse width to subtract fuel from the air/fuel mixture to lean out the air/fuel mixture because the input data it is receiving tells it that the mixture is too rich.
What is a good long term fuel trim reading?
Both LTFT and STFT can be positive (more fuel) or negative (less fuel) percentages. LTFT and STFT are added together to produce the total fuel trim, and neither should exceed ± 10% in normal operating conditions. Fuel trims (LTFT, STFT, or LTFT+STFT) exceeding ±10% may indicate a problem in the engine or the sensors.
What is St fuel trim?
In short, fuel trim describes the adjustments that a vehicle’s engine control unit (ECU) makes to the fuel delivery system to keep the air-fuel mixture as close to its ideal ratios as possible.
Why do I have negative fuel trim?
But when the engine is in boost mode and positive pressure is provided in the intake, the vacuum leak will allow boost air to escape. This causes the fuel trim numbers to become negative during a boost situation. This happens because the PCM is supplying fuel for the amount of air the MAF sensor measured.
What causes negative fuel trim at idle?
The MAF sensor overestimates airflow at idle, which causes the negative fuel trim values. It then underestimates airflow at cruising speeds, which accounts for the positive fuel trim values.
What does the fuel trim error code p0170 mean?
For American cars, the most common fuel trim error codes are P0171, P0174, P0172, P0175, which refer to fuel trim malfunctions. Meaning, there is very little information about P0170 and P0173.
How much does it cost to diagnose a p0171 Chevron code?
The cost to diagnose the P0171 CHEVROLET code is 1.0 hour of labor. The auto repair’s diagnosis time and labor rates vary by location, vehicle’s make and model, and even your engine type.
What does the O2 sensor code p0171 mean on a car?
If the P0171 is combined with the P0174 code, it’s very likely that the problem is caused by an intake leak. If there are no intake leaks, the next step is to replace the air filter and clean the air flow meter. If the problem persists the front oxygen (O2) sensor may need to be replaced.
What does the p0173 code on a Mercedes Benz mean?
It may also have a P0173 referring to the same malfunction but on bank two. Potential causes include a vacuum leak, unmetered air leaks Fuel saturated engine oil Leak in turbo air charge hoses (if equipped) Possibly bad O2 sensor (If Mercedes, may require adaptation with M-Benz compatible scan tool.)