The Mass Air Flow Sensor
(MAFS) is located between the air cleaner assembly and the throttle body.
The MAFS uses a hot film type sensing element to measure the mass of
intake air entering the engine. This hot film type air flow sensor
consists of a hot film sensor, housing and metering ducts. Mass air flow
rate is measured by detection of heat transfer from a hot film probe. The
change in air flow rate causes change in the amount of heat being
transferred from the hot film probe surface to the air. A large amount of
intake air represents acceleration or high load conditions while a small
amount of intake air represents deceleration or idle. The mass of intake
air should increase at acceleration and be stable during constant engine
speed. The PCM uses this information to determine the injection duration
and ignition timing for the desired air/fuel ratio.
If PCM detects that
frequency signal of MAFS is higher thatn 11900 Hz for more than 75 second
during 125 second dignostic test while enable condition is met, PCM
determines that a fault exists and a DTC is stored. MIL(Malfunction
Indication Lamp) turns on when the malfunction lasts till consecutive 2
driving cycle.
Item
|
Detecting
Condition
|
Possible cause
|
DTC
Strategy
|
| •
|
Compares the airmeter input frequency to
a high limit | |
|
Enable
Conditions
|
| •
|
Engine Running Time ≥ 5
second |
|
Threshold
value
|
| •
|
MAF frequency signal >
11900Hz | |
Diagnosis
Time
|
| •
|
Continuous
(More than 75 second failure for every
125 second tests ) | |
MIL On
Condition
|
|
Air Flow (kg/h)
|
Frequency (Hz)
|
12.6
|
2617.0
|
18.0
|
2958.0
|
23.4
|
3241.0
|
32.4
|
3653.0
|
43.2
|
4024.0
|
57.6
|
4399.0
|
72.0
|
4704.0
|
108.0
|
5329.0
|
144.0
|
5897.0
|
198.0
|
6553.0
|
270.0
|
7240.0
|
360.0
|
7957.0
|
486.0
|
8738.0
|
666.0
|
9644.0
|
900.0
|
10590.0
|
| 1. |
Check DTC Status
| (1) |
Connect scantool to Data Link
Connector(DLC). |
| (3) |
Select "DTC" button, and then Press "DTC
Status" to check DTC's information from the DTCs
menu. |
| (4) |
Read "DTC Status"
parameter.
|
| (5) |
Is parameter displayed "Present
fault"?
|
|
▶ Go
to "Terminal and connector inspection"
procedure.
|
|
|
▶
Fault is intermittent caused by poor contact in the
sensor's and/or PCM's connector or was repaired and PCM
memory was not cleared. Thoroughly check connectors for
looseness, poor connection, ending, corrosion,
contamination, deterioration, or damage. Repair or
replace as necessary and go to "Verification of Vehicle
Repair"
procedure.
|
| |
| Terminal And Connector
Inspection |
| 1. |
Many malfunctions in the electrical system are
caused by poor harness and terminal condition. Faults can also be
caused by interference from other electrical systems, and mechanical
or chemical damage. |
| 2. |
Thoroughly check connectors for looseness,
poor connection, bending, corrosion, contamination, deterioration,
or damage. |
| 3. |
Has a problem been found?
|
|
▶ Repair or
replace if necessary and go to "Verification of Vehicle
Repair" procedure
|
|
|
▶ Go to
"Ground Circuit Inspection"
procedure.
|
|
| Ground Circuit
Inspection |
■ Check open in harness
| 1. |
IG "OFF" and disconnect MAFS connector and
then IG "ON". |
| 2. |
Measure voltage between signal terminal of
MAFS harness connector and chassis ground (Measurement
"A") |
| 3. |
Measure voltage between signal and ground
terminals of MAFS harness connector (Measurement "B")
Specification
: Voltage difference between
Measurement "A" and "B" is below 200mV.
| |
| 4. |
Is the measured voltage within the
specification?
|
|
▶ Go to
"Component Inspection".
|
|
|
▶ After
repairing or replacing contact resistance in ground circuit
and open in the MAFS circuit, go to "Verification and Vehicle
Repair".
|
|
| 1. |
Visual Inspection
| (1) |
Check that MAFS is damaged, contaminated
or deformed. |
| (2) |
Has a problem been found ?
|
|
▶
Repair or replace as necessary and then go to
"Verification of Vehicle Repair"
procedure.
|
|
|
▶ Go
to "Check MAFS" as
follows
|
| |
| 2. |
Check MAFS
| (1) |
IG "OFF" and install a
scantool |
| (2) |
ENG "ON" and monitor "MAFS" data on the
service data. |
| (3) |
Monitor signal waveform at signal
terminal of MAFS with scantool.
Specification :Signal
waveform will be displayed as follows. (Be aware that
the signal of MAFS is not voltage display but frequency
display.)
|
|
| (4) |
Are both service data and signalwave
form dispayed correctly ?
|
|
▶
Substitute with a known - good PCM and check for proper
operation. If the problem is corrected, replace PCM and
go to "Verification of Vehicle Repair"
procedure.
|
There is a memory reset
function on scantool that can erase optional parts
automatically detected and memorized by PCM.
Before or after testing PCM on the vehicle, use
this function to reuse the PCM on the
others. | |
|
|
▶
Substitute with a known - good MAFS and check for proper
operation. If the problem is corrected, replace MAFS and
go to "Verification of Vehicle Repair"
procedure.
|
| |
| Verification Of Vehicle
Repair |
After a repair, it is
essential to verify that the fault has been corrected.
| 1. |
Connect scantool and select "DTC"
button. |
| 2. |
Press "DTC Status" button and confirm that
"DTC Readiness Flag" indicates "Completed". If not, drive the
vehicle within conditions noted in the freeze frame data or enable
conditions |
| 3. |
Read "DTC Status"
parameter |
| 4. |
Is parameter displayed "History(Not Present)
fault"?
|
|
▶ System
performing to specification at this time. Clear the
DTC
|
|
|
▶ Go to the
applicable troubleshooting
procedure.
|
|
