Error Codes

Hi all!

My 2009 Tacoma (~195,000 miles) recently had the following error codes: P0171 and P0174 (System Too Lean Bank 1 and 2). My check engine light and traction control light are also on. Just wondering if anyone has experienced anything similar, and what the possible causes are? Thanks!

 

DTC No.:

P0171, P0174

DTC Detection Conditions:

With warm engine and stable air-fuel ratio feedback, fuel trim considerably in error to lean side (2 trip detection logic).

Possible causes:

• Air induction system
• Injector blockage
• Mass Air Flow (MAF) meter
• Engine Coolant Temperature (ECT) sensor
• Fuel pressure
• Gas leakage from exhaust system
• Open or short in A/F sensor (bank 1, 2 sensor 1) circuit
• A/F sensor (bank 1, 2 sensor 1)
• A/F sensor heater (bank 1, 2 sensor 1)
• A/F sensor heater relay
• A/F sensor heater and A/F sensor heater relay circuits
• PCV valve and hose
• PCV hose connections
• ECM

ES–152 1GR-FE ENGINE CONTROL SYSTEM – SFI SYSTEM
ES
DESCRIPTION
The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim
consists of both the short-term and long-term fuel trims.
The short-term fuel trim is fuel compensation that is used to constantly maintain the air-fuel ratio at
stoichiometric levels. The signal from the Air-Fuel Ratio (A/F) sensor indicates whether the air-fuel ratio is
rich or lean compared to the stoichiometric ratio. This triggers a reduction in the fuel injection volume if the
air-fuel ratio is rich and an increase in the fuel injection volume if it is lean.
Factors such as individual engine differences, wear over time and changes in operating environment
cause short-term fuel trim to vary from the central value. The long-term fuel trim, which controls overall
fuel compensation, compensates for long-term deviations in the fuel trim from the central value caused by
the short- term fuel trim compensation.
If both the short-term and long-term fuel trims are lean or rich beyond predetermined values, it is
interpreted as a malfunction, and the ECM illuminates the MIL and sets a DTC.
HINT:
• When DTC P0171 or P0174 is set, the actual air-fuel ratio is on the lean side. When DTC P0172 or P0175 is set, the actual air-fuel ratio is on the rich side.
• If the vehicle runs out of fuel, the air-fuel ratio is lean and DTC P0171 or P0174 may be set. The MIL is then illuminated.
• When the total of the short-term and long-term fuel trim values is within the malfunction threshold (and the engine coolant temperature is more than 75°C [167°F]), the system is functioning normally.

Description:

The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim consists of both the short-term and long-term fuel trims.
The short-term fuel trim is fuel compensation that is used to constantly maintain the air-fuel ratio at stoichiometric levels. The signal from the Air-Fuel Ratio (A/F) sensor indicates whether the air-fuel ratio is rich or lean compared to the stoichiometric ratio. This triggers a reduction in the fuel injection volume if the air-fuel ratio is rich and an increase in the fuel injection volume if it is lean. Factors such as individual engine differences, wear over time and changes in operating environment cause short-term fuel trim to vary from the central value. The long-term fuel trim, which controls overall fuel compensation, compensates for long-term deviations in the fuel trim from the central value caused by the short- term fuel trim compensation. If both the short-term and long-term fuel trims are lean or rich beyond predetermined values, it is interpreted as a malfunction, and the ECM illuminates the MIL and sets a DTC.

 

Lean codes, need to look at long and short term fuel trims during various driving conditions to see what kind of lean condition we are dealing with.

 

Got the reading, and it is showing the following long and short-term fuel trims:

Shrtft1% at 7.8
Shrtft2% at 3.9
Longft1% at 19.5
Longft2% at 19.5

 

Is this at idle or under load?

 

Sorry, forgot to mention it was at idle.

 

Do they get better, worse, or stay the same under load?