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.
If a MAFS need to be replaced, make sure the sensor is learned to the system while using scan tool. If the MAFS is not learned to the system, it may cause vehicle performance and exhaust gas problem.
P0101 is set 1) when mass air flow sensor or intake air temperature senser is short to battery or ground or 2) short to battery or ground in MAFS or IATS signal circuit is detected or 3) short to low or high voltage line in IATS signal circuit is detected.
Item
Detecting Condition
Possible Cause
DTC Strategy
Voltage monitoring
AFS circuit
AFS
Enable Conditions
Engine running
Threshold Value
Short to battery in MAFS or ITAS circuit. - 7000ms
Short to ground in MAFS or ITAS circuit. - 7000ms
Short to battery in ITAS circuit. - 600ms
Short to ground in ITAS circuit. - 600ms
Fail Safe
Fuel cut
NO
-
EGR Off
YES
Fuel Limit
Check Lamp
OFF
status of engine
Frequency (Hz) - MAFS
reference
sensor
IG key on
18.9
approx. 1846
idle
19.9
approx. 2195
Fig.1) The waveform at IG Key ON
Fig.2) The waveform at idle
[Fig.1] The signal waveform of MAFS at IG key ON.
- Duty : approx. 50%,
- Frequency : 1.8 KHz
[Fig.2] The signal waveform of MAFS at idle (800rpm)
- Duty : approx. 50%
- Frequency : 2.0 ~ 2.5 KHz
? The higher engine RPM, the higher output frequency.