DTC P0171, DTC P0172, DTC P0174 & DTC P0175: Notes

WARNING: This page is about a different car, the 2003 Toyota 4Runner. However, it is still accessible from the selected car via links, so may be relevant.

Code Definition

DTC P0171: System Too Lean (Bank 1)
DTC P0172: System Too Rich (Bank 1)
DTC P0174: System Too Lean (Bank 2)
DTC P0175: System Too Rich (Bank 2)

CAUTION: If Engine Control Module (ECM) replacement is instructed in following test, always ensure ECM electrical connectors and ground circuits are okay. If either are defective, repair and repeat testing to confirm ECM malfunction. On models equipped with engine immobilizer, if ECM is replaced, ECM must be programmed with proper ignition key code for engine immobilizer system. For programming procedures, see COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION, or appropriate ENGINE IMMOBILIZER SYSTEMS article in ACCESSORIES & EQUIPMENT.

NOTE: These DTCs may be caused by the vehicle running out of fuel. If the vehicle runs out of fuel, the air-fuel ratio is LEAN and DTCs P0171 or P0174 is recorded. The MIL then comes on.

NOTE: If DTCs related to MAF, IAT, TPS, ECT, HO2S and/or A/F sensor are output simultaneously, the E2 sensor ground circuit at ECM 34-pin connector E4 terminal No. 28 (Brown wire) may be open. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. For ECM connector terminal identification, see Figure.