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DTC P1238: Mass Airflow Sensor Plausibility (Torque Monitor)
 
 
 
 
TECHNICAL DESCRIPTION
Compare the actual measurement of volumetric efficiency by a mass airflow sensor signal with volumetric efficiency estimated from a throttle position sensor (main or sub) signal.
 
 
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)
  • Not applicable
Sensor (The sensor below is determined to be normal)
  • Throttle position sensor
 
 
DTC SET CONDITIONS
Logic Flow Chart
Check Conditions
  • The volumetric efficiency estimated by the throttle position sensor (main) subtracted from the actual volumetric efficiency is higher than 0 percent. Or, the volumetric efficiency is 60 percent or lower.
  • Engine speed is 750 r/min or higher.
Judgment Criterion
  • For 4.5 second, the difference between the actual volumetric efficiency and the volumetric efficiency estimated by the throttle position sensor (main) is higher than 35 percent.
Check Conditions
  • The volumetric efficiency estimated by the throttle position sensor (sub) subtracted from the actual volumetric efficiency is higher than 0 percent. Or, the volumetric efficiency is 60 percent or lower.
  • Engine speed is 750 r/min or higher.
Judgment Criterion
  • For 4.5 second, the difference between the actual volumetric efficiency and the volumetric efficiency estimated by the throttle position sensor (sub) is higher than 35 percent.
 
 
FAIL-SAFE AND BACKUP FUNCTION
  • Throttle opening degree position is in default position.
 
 
OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle Pattern 1 .
 
 
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
  • Mass airflow sensor system failed.
  • Intake system vacuum leak.
  • ECM 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 off the power supply mode of the electric motor switch before connecting or disconnecting scan tool (M.U.T.-IIISE).
(1) Connect scan tool (M.U.T.-IIISE). Refer to HOW TO CONNECT THE SCAN TOOL (M.U.T.-IIISE) .
(2) Turn on the power supply mode of the electric motor switch.
(3) Read the DTC.
(4) Turn off the power supply mode of the electric motor switch.
Is the diagnostic trouble code other than P1238 set?
Refer to Diagnostic Trouble Code Chart .
Go to Step 2.
 
STEP 2. Check for intake system vacuum leak.
Are there any abnormalities?
Repair it. Then go to Step 5.
Go to Step 3.
 
STEP 3. Using scan tool (M.U.T.-IIISE), check data list item 10: Mass Airflow Sensor.
(1) Set the vehicle to the continuous idling mode.
(2) Set scan tool (M.U.T.-IIISE) to the data reading mode for item 10, Mass Airflow Sensor.
(3) Warm up the engine.
  • The standard value should be between 880 and 1,280 millivolts.
  • When the engine is revved, the output voltage should increase according to the increase in engine speed.
(4) Turn off the power supply mode of the electric motor switch.
Is the sensor operating properly?
Go to Step 4.
Refer to DTC P0102 - Mass Airflow Circuit Low Input , DTC P0103 - Mass Airflow Circuit High Input .
 
STEP 4. Check the trouble symptoms.
(1) Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle Pattern 1 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P1238 set?
Replace the ECM (Refer to Removal and Installation ). Then go to Step 5.
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 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 1 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P1238 set?
Retry the troubleshooting.
The inspection is complete.