DTC Advanced Diagnostics: P0171
DTC P0171:Fuel System Too Lean

General Description

The powertrain control module (PCM) monitors the fuel mixture adaptation system. The fuel mixture adaptation system corrects fuel mixture deviations from the fuel control system with the following error compensation terms:

The multiplicative correction term FRA: dominates the total fuel correction at higher engine speeds and loads.

The additive correction term ORA: dominates the total fuel correction at idle.

This is only possible when closed loop fuel control is active and during homogeneous operation with stoichiometric ratio. If the multiplicative part of the long term fuel trim or the additive part of the long term fuel trim is greater than a specified value, the PCM detects a malfunction and stores a DTC. The PCM also monitors the short term fuel trim value. If the short trim fuel trim value is a specified value, the PCM detects a malfunction and stores a DTC.

Monitor Execution, Sequence, Duration, DTC Type
Execution
Multiple*, Continuous**
Sequence
None
Duration
0.5 second or more*, 100 seconds or more**
DTC Type
Two drive cycles, MIL on
*: Long term fuel trim
**: Short term fuel trim

Enable Conditions
Long term fuel trim
Condition
 
Other
Multiplicative part of the long term fuel trim or the additive part of the long term fuel trim is enabled
Excessive fuel must not be contained in engine oil
Multiplicative part is stable for at least 10 seconds***
***: Monitor for additive part

Short term fuel trim
Condition
Minimum
Maximum
Engine coolant temperature [ECT Sensor 1]
140 °F (60 °C)
–
Fuel injection time
1,560 times
–
Fuel feedback
Closed loop
Other
Evaporative emission (EVAP) canister not purging for at least 10 seconds
Excessive fuel must not be contained in engine oil
[ ]: HDS Parameter

Malfunction Threshold
Any of the conditions is met:
Monitor for multiplicative part of long term fuel trim
The multiplicative part of long term fuel trim is more than 1.30 for at least 10 seconds.
Monitor for additive part of long term fuel trim
The additive part of long term fuel trim is more than 5.48 % for at least 10 seconds.
Monitor for short term fuel trim
The deviation of the short trim fuel trim mean value from 1.0 is higher than 0.24.

Possible Cause
NOTE: The causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes.
Exhaust gas leak
Mass airflow (MAF) sensor failure
Fuel injector failure
Fuel control system failure

Confirmation Procedure
Operating Condition
1.
Start the engine. Hold the engine speed [Engine Speed] at 3,000 rpm without load (in neutral) until the radiator fan comes on.
2.
Drive the vehicle at high engine speed and high load for a while.
Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.

Diagnosis Details
Conditions for setting the DTC
When a malfunction is detected during the first drive cycle, a Pending DTC is stored in the PCM memory. If the malfunction returns in the next (second) drive cycle, the MIL comes on and a Confirmed DTC and the freeze data are stored.

Conditions for clearing the DTC
The MIL is cleared if the malfunction does not return in three consecutive drive cycles in which the engine conditions are similar to the first time the malfunction was detected. The MIL, the Pending DTC, the Confirmed DTC, and the freeze data can be cleared with the scan tool Clear command.