Mass Air Flow Sensor (MAFS) is digital sensor. Measuring mass of air flow, signal is outputted as frequency(Hz). ECM performs EGR system feed back control with the information of measured mass air flow. (The role of MAFS in diesel engine is different from gasoline engine. Fuel injection quantity is decided by MAFS signal in gasoline engine.)
When the amount of EGR gas(contains no oxygen) flowing into combustion chamber increases, the air passing through MAFS(contains oxygen) decreases. Thus, with the output signal change of MAFS accompanied by EGR actuator actuation, ECM determines the amount of recirculated EGR gas quantity.
NOx is produced in the reaction of nitrogen and oxygen. If least intake air required for complete combustion flows into combustion chamber by controlling EGR gas(contains no oxygen) which is recirculated to combustion chamber, NOx decreases because there is no supplementary oxygen to react with nitrogen.
P0102 is set when MAFS output voltage below 0.2V(below 1200Hz) is detected for more than 0.6 sec.. This code is due to 1)open in power circuit 2) open or short to ground in signal circuit.
Item | Detecting Condition | Possible Cause | ||
DTC Strategy | ● Voltage monitoring | ● AFS circuit ● AFS component | ||
Enable Conditions | ● Engine running | |||
Threshold Value | ● Abnormal minimum output signal( below 1200Hz ) | |||
Diagnostic Time | ● 0.6 sec. | |||
Fail Safe | Fuel cut | NO | ||
EGR Off | YES | |||
Fuel Limit | YES | |||
Check Lamp | YES | |||
Signal frequency increases as RPM rises.
Intake air quantity (Kg/h) | Output frequency ( KHz ) | deviation [ % ] | |
20℃ | 80℃ | ||
8 | 1.97 | ±3 | |
10 | 2.01 | 2.01 | ±2 |
40 | 2.50 | 2.50 | ±2 |
105 | 3.20 | 3.20 | ±2 |
220 | 4.30 | ±2 | |
480 | 7.80 | 7.80 | ±2 |
560 | 9.50 | ±3 | |
Connect Scantool to Data Link Connector (DLC).
Warm engine up to normal operating temperature.
Turn "OFF" electrical devices and A/C.
Monitor "AIR MASS PERCYLINDER" parameter on the Scantool.
Specification : When EEGR actuator does not operate 5% duty) at idle : 450mg/st ± 50 mg/st
When EEGR actuator operates(Approx. 50% duty) at idle : 300mg/st ± 50 mg/st
EEGR actuator operates as decelerating after rapid acceleration when idle EEGR does not operate, EEGR actuator duty rises to approx. 45% at operating condition. This controlling process lasts for about 56 sec. then EEGR actuator turns "OFF" (duty 5% ).
Electrical systems consist of a lot of harness and connectors, poor connection of terminals can cause various problems and damge of component.
Perform checking procedure as follows.
Check damage of harness and terminals : Check terminals for contact resistance, corrosion and deformation.
Check connecting condition of ECM and component connector : Check terminal seperation, damage of locking device and
Disconnect the pin which requires checking at male connector and insert it to the terminal at female connector for checking connecting condition. ( after checking, reconnect the pin at correct position. )
Is the problem found?
▶ Repair the trouble causing part and go to "Verification of Vehicle Repair".
▶ Go to "Power Circuit Inspection".
Check power circuit voltage
IG KEY "OFF", ENGINE "OFF".
Disconnect MAFS connector.
IG KEY "ON".
Measure the voltage of MAFS connector terminal 1 and 4.
Specification : Terminal 4 : 4.8V~5.1V ( Sensor power )
Terminal 1 : 11.5V~13.0V ( IG Power )
Is the measured voltage within the specification?
▶ Go to "Signal Circuit Inspection".
▶ When output voltage is not detected at terminal 1 :
☞ Repair open in E/R junction box 10A ECU FUSE and related circuit and go to "Verification of Vehicle Repair".
▶ When output voltage is not detected at terminal 4 :
☞ Repair open between MAFS connector terminal 4 and ECM connector terminal 37, and go to "Verification of Vehicle Repair".
Check signal circuit voltage
IG KEY "OFF", ENGINE "OFF".
Disconnect MAFS connector.
IG KEY "ON".
Measure the voltage of MAFS connector terminal 5.
Specification : 4.8V~5.1V
Is the measured voltage within the specification?
▶ Go to "Ground Circuit Inspection".
▶ Go to "2. Check open in signal circuit" as follows.
Check open in signal circuit
IG KEY "OFF", ENGINE "OFF".
Disconnect MAFS sensor connector and ECM connector.
Check continuity between MAFS connector terminal 5 and ECM connector(C244-A) terminal 42.
specification : Continuity ( below 1.0Ω )
Is the measured resistance within the specification?
▶ Go to "3. Check short to ground in signal circuit" as follows.
▶ Repair open in signal circuit and go to "Verification of Vehicle Repair".
Check short to ground in signal circuit
IG KEY "OFF", ENGINE "OFF".
Disconnect MAFS connector and ECM connector.
Check continuity between MAFS connector terminal 5 and chassis ground.
Specification : Discontinuity(Infinite Ω )
Is the measured resistance within the specification?
▶ Go to "Ground Circuit Inspection".
▶ Repair short to ground in signal circuit and go to "Verification of Vehicle Repair".
IG KEY "OFF", ENGINE "OFF".
Disconnect MAFS connector.
IG KEY "ON".
Measure the voltage of MAFS connector terminal 4. [ TEST "A" ]
Measure the voltage between MAFS connector terminal 4 and 2. [ TEST "B" ]
( terminal 4 : Check + prove , terminal 2 : Check - prove )
Specification : [TEST "A"] Voltage - [TEST "B"] Voltage = below 200mV
Is the measured voltage within the specification?
▶ Go to "Component Inspection".
▶ When "B" voltage is not detected : Repair open in ground circuit and go to "Verification of Vehicle Repair".
▶ When the voltage difference between "A" and "B" is above 200mV : Eliminate the causes of excessive resistance and go to "Verification of Vehicle Repair".
IG KEY "OFF", ENGINE "OFF".
Check that AFS is installed in correctly according to the direction of arrow on AFS assy'.
Check contamination of air cleaner filter.
IG KEY "ON", ENGINE "ON".
Let IDLE RPM last after warming engine up.
Check the leakage of intake system(the leakage or damage of intercooler).
Check that VGT operates correctly.( Check if vacuum operating state of VGT actuator is appropriate, if VGT diaphragm and unison ring are stuck.)
Check that EEGR actuator does not operate.
( EEGR actuator turns "OFF" and 5.9% duty is outputted 1 min. after rapid acceleration. )
Monitor signal voltage of AFS when engine speed lasts at approx. 800RPM using Scantool.
Check AFS output signal at idle after rapid acceleration.(EEGR actuator duty 50%)
Specification : When EEGR actuator does not operate (5%) at idle : 450mg/st ± 50 mg/st
EEGR When EEGR actuator operates(50%) at idle : 300ms/st ± 50 mg/st
Is output signal within the specification?
▶ Go to "Verification of Vehicle Repair".
▶ Replace MAFS assy' and go to "Verification of Vehicle Repair".
After a repair, it is essential to verify that the fault is corrected.
After connecting Scantool select "DIAGNOSTIC TROUBLE CODES(DTCs)" mode.
Clear recorded DTC using Scantool.
Drive the vehicle within DTC "Enable conditions" in "General information".
After selecting "DIAGNOSTIC TROUBLE CODES(DTCs)" mode and check if DTC is recorded again.
Are any DTCs recorded ?
▶ Go to the DTC guide of recorded NO. in Scantool.
▶ System operates within specification.
