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DTC P129A: Fuel Trim (MFI)
 
 
 
 
TECHNICAL DESCRIPTION
The cause may mainly lie in an abnormally rich air-fuel ratio or abnormally lean air-fuel ratio, due to the poor injector.
 
 
DESCRIPTIONS OF MONITOR METHODS
After too lean or rich (DTC P0171 or P0172) is detected at MFI mode, sum of DFI air fuel ratio feedback compensation values is monitored at DFI and MFI mode.
 
 
MONITOR EXECUTION
  • Continuous
 
 
MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)
Other Monitor (There is no temporary DTC set in memory for the item monitored below)
  • Misfire monitor
Sensor (The sensor below is determined to be normal)
  • Mass airflow sensor
  • Engine coolant temperature sensor
  • Intake air temperature sensor 1
  • Barometric pressure sensor
  • Throttle position sensor
  • Manifold absolute pressure sensor
 
 
DTC SET CONDITIONS
Logic Flow Chart
 
 
Check Conditions
  • The malfunction of DTC P0171 or P0172 is detected in MFI mode.
  • Engine coolant temperature is higher than 76°C (169°F).
  • Under the closed loop air/fuel ratio control.
  • Mass airflow sensor output is 9 g/sec or more.
  • Fuel injection mode is not MFI-mode.
  • During the drive cycle, the ECM performs monitoring with the accumulated total time of 20 seconds.
Judgment Criterion
  • Sum of DFI long-term fuel trim and short-term fuel trim is between 0.820 and 1.195.
 
 
FAIL-SAFE AND BACKUP FUNCTION
  • None.
 
 
OBD-II DRIVE CYCLE PATTERN
  • Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 8 .
 
 
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are: )
  • Injector failed.

 
 
DIAGNOSIS
STEP 1. Using scan tool (M.U.T.-IIISE), read the diagnostic trouble code (DTC).
cautionTo prevent damage to scan tool (M.U.T.-IIISE), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-IIISE).
(1) Connect scan tool (M.U.T.-IIISE) to the data link connector.
(2) Turn the ignition switch to the "ON" position.
(3) Set scan tool (M.U.T.-IIISE), read the DTC.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the DTC P0171 or P0172 set?
Go to Step 2.
Replace the ECM (Refer to Removal and Installation ). Then go to Step 5.
 
STEP 2. Check the injector.
Refer to Injector Check .
Is the measured resistance normal?
Go to Step 3.
Replace the faulty injector. Then go to Step 5.
 
STEP 3. Check the trouble symptoms.
(1) Carry out test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 8 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P129A set?
Replace the all injector. Then go to Step 4.
It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions .
 
STEP 4. Check the trouble symptoms.
(1) Carry out test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 8 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P129A set?
Refer to DTC P0171 - System too Lean , DTC P0172 - System too Rich .
The inspection is complete.
 
STEP 5. Test the OBD-II drive cycle.
(1) Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 8 .
(2) Check the diagnostic trouble code (DTC).
Is the DTC P129A set?
Retry the troubleshooting.
The inspection is complete.