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 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 from 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 | ● MAFS circuit ● MAFS 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 |
Intake air quantity (Kg/h) | Output frequency ( KHz ) | Deviation [ % ] | |
20℃ | 80℃ | ± 3 | |
8 | 1.97 | ± 2 | |
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 |
Fig.1) MAFS signal waveform at IG KEY "ON". It shows digital signal of 50% duty, 1.8KHz.
Fig.2) MAFS signal waveform at idle(800RPM, EEGR actuator duty 4.4%, air flow for each cylinder 450mg/st).
It shows digital signal of 50% duty, 2.0~2.5KHz.
Signal frequency increases as RPM rises.
