P0170

DTC PO17O - Fuel Trim Malfunction

CIRCUIT DESCRIPTION
"Fuel trim" refers to the feedback compensation value compared against the basic injection time. Fuel trim includes short-term fuel trim and long-term fuel trim.

"Short-term fuel trim" is the short-term fuel compensation used to maintain the air-fuel ratio at its ideal theoretical value. The signal from the heated oxygen sensor indicates whether the air-fuel ratio is RICH or LEAN compared to the ideal theoretical value, triggering a reduction in fuel volume if the air-fuel ratio is rich, and an increase in fuel volume if it is lean.

"Long-term fuel trim" is overall fuel compensation carried out long-term to compensate for continual deviation of the short-term fuel trim from the central value due to individual engine differences, wear over time and changes in the usage environment.

If both the short-term fuel trim and long-term fuel trim are LEAN or RICH beyond a certain value, it is detected as a malfunction and the MIL lights up.

DETECTING CONDITION



HINTS:
- If the vehicle runs out of fuel, the air/fuel ratio is LEAN and DTC P0170 is detected. The MIL then comes ON.
- Fuel trim applies separately to bank 1 and bank 2, so the ECM lights up the MIL if a problem occurs with either bank.
- You can tell which bank is malfunctioning by looking at the short-term and long-term fuel trim, thus allowing you to focus your inspection.
- If the total of short-term fuel trim and long-term fuel trim for each bank is within ±25%, the system is functioning normally.


INSPECTION PROCEDURE