Fuel trim malfunction

P0170 - Rear (RH) bank

P0173 - Front (LH) bank

Detection Condition

• The ECU monitors short-term fuel trim (SHRTFT) and long-term fuel trim (LONGFT) values when DRIVE MODE 1 conditions have been met. If fuel trim exceeds a preprogrammed threshold, the ECU determines that there is a fuel system malfunction.

Diagnostic Support Notes

• This is a continuous monitor (FUEL SYSTEM)
• The check engine indicator illuminates if the ECU detects the above malfunction condition in two consecutive drive cycles
• PENDING CODE is available
• FREEZE FRAME DATA is available
• DTC is stored in ECU memory

Possible Causes

• Combustion misfire
• Upstream oxygen sensor deterioration
• Upstream oxygen sensor (heater circuit) malfunction
• Fuel pressure regulator control (PRC) solenoid valve malfunction
• Fuel pressure regulator malfunction
• Fuel pump malfunction
• Fuel filter restriction
• Fuel system pressure leak
• Fuel return hose restriction
• Exhaust system leakage
• Purge solenoid valve malfunction
• Purge solenoid hoses misrouted
• PCV valve malfunction
• Insufficient engine compression

[P0170 / P0173 - From 2002 Mazda Millenia factory service manual]