Circuit Description
The Mass Air Flow (MAF) sensor measures the amount of air ingested by
the engine. The direct measurement of the air entering the engine is more
accurate than calculating the airflow from the MAP, the IAT and the engine
speed (speed/density). The MAF sensor has a battery feed, ground, and a signal
circuit.
The MAF sensor used on this engine is a hot wire type. This engine uses
the MAF sensor to measure air flow rate. The MAF output frequency is a function
of the power required to keep the air flow sensing elements (hot wires) at
a fixed temperature above the ambient temperature. Air flowing through the
sensor cools the sensing elements. The amount of cooling is proportional to
the amount of air flow. As the air flow increases, the MAF sensor requires
a greater amount of current in order to maintain the hot wires at a constant
temperature. The MAF sensor converts the changes in current draw to a frequency
signal read by the PCM. The PCM calculates the air flow (grams per second)
based on this signal.
The PCM monitors the MAF sensor frequency. The PCM can determine if
the sensor is stuck low, stuck high, not providing the airflow value expected
for a given operating condition, or that the signal appears to be stuck based
on a lack of signal variation expected during the normal operation. This diagnostic
checks the range/performance of the MAF sensor. The MAF system performance
or rationality diagnostic uses the MAP, the IAT, and the engine speed to calculate
an expected airflow rate. The PCM then compares the rate to the actual measured
airflow from the MAF sensor. The PCM only compares the actual MAF value and
the calculated value during conditions where the values are likely to match.
If the actual MAF reading is not within a predetermined range of the calculated
reading, this DTC will set.
Step
| Action
| Value(s)
| Yes
| No
|
1
| Did you perform the Powertrain
On-Board Diagnostic (OBD) System Check?
| --
|
Go to Step 2
| Go to
Powertrain On Board Diagnostic (OBD) System Check
|
2
| If any MAP sensor DTCs are
set, refer to the applicable DTC before proceeding.
ImportantThis value will vary with altitude. Refer to Test
Description.
- Turn ON the ignition leaving the engine OFF.
- Monitor the MAP sensor display in the Engine 1 Data List using
the scan tool.
Is the value displayed greater than the value shown?
| 100 kPa
|
Go to Step 3
|
Go to Step 19
|
3
|
- Remove the MAP sensor from the intake manifold but leave the electrical
harness connected.
- Connect a hand operated vacuum pump to the MAP sensor.
- Observe the MAP sensor display while slowly applying vacuum up
to 20 inches Hg as indicated on the pump gauge. Each 1 inch of vacuum applied
should result in a 3 to 4 kPa drop in the MAP sensor value on the scan
tool and the value should change smoothly with each increase in vacuum.
Did the MAP sensor value change smoothly through the entire range of
the test without any erratic readings?
| --
|
Go to Step 4
|
Go to Step 19
|
4
| Apply 20 inches Hg
vacuum to the MAP sensor.
Is the MAP sensor reading on the scan tool the same or less than the
specified value?
| 34 kPa
|
Go to Step 5
|
Go to Step 19
|
5
| Disconnect the vacuum source
from the MAP sensor.
Does the MAP sensor reading return to the original value?
| --
|
Go to Step 6
|
Go to Step 19
|
6
|
- Turn ON the ignition leaving the engine OFF.
- Review the Freeze Frame and/or Failure Records data for this DTC
and observe the parameters.
- Turn OFF the ignition for 15 seconds.
- Start the engine.
- Operate the vehicle within the conditions required for this diagnostic
to run, and as close to the conditions recorded in the Freeze Frame/Failure
Records as possible. Special operating conditions that you need to meet before
the PCM will run this diagnostic, where applicable, are listed in Conditions
for Setting the DTC.
- Select the Diagnostic Trouble Code (DTC) option, the Specific
DTC option, then enter the DTC number using the scan tool.
Does the scan tool indicate that this diagnostic failed this ignition?
| --
|
Go to Step 7
| Go to Diagnostic
Aids
|
7
|
- Check for the following conditions:
- Objects blocking the MAF sensor inlet screen
- Intake manifold vacuum leaks
- Vacuum leaks at the throttle body
- Crankcase ventilation valve faulty, missing, or incorrectly installed
- If you find a condition, repair as necessary.
Did you find and correct the condition?
| --
|
Go to Step 21
|
Go to Step 8
|
8
|
- Turn OFF the ignition.
- Disconnect the MAF sensor connector.
- Turn ON the ignition leaving the engine OFF.
- Measure the voltage between the MAF sensor signal circuit and
the battery ground using the DMM
.
Is the voltage near the specified value?
| 5.0V
|
Go to Step 9
|
Go to Step 10
|
9
| Connect a test lamp
between the MAF sensor ignition feed
and the ground circuit at the MAF sensor harness connector.
Is the test lamp illuminated?
| --
|
Go to Step 13
|
Go to Step 12
|
10
| Is the voltage less than the
specified value?
| 4.5V
|
Go to Step 14
|
Go to Step 11
|
11
|
- Turn OFF the ignition.
- Disconnect the PCM connector located on the opposite side of the
manufacturer's logo. Refer to
PCM/TAC Module Replacement
.
- Turn ON the ignition leaving the engine OFF.
- Measure the voltage between the MAF sensor signal circuit and
ground.
Does the voltage measure near the specified value?
| 0.0V
|
Go to Step 20
|
Go to Step 17
|
12
| Connect a test lamp
between the MAF sensor ignition feed circuit and the battery ground.
Is the test lamp illuminated?
| --
|
Go to Step 15
|
Go to Step 16
|
13
|
- Check for a poor connection at the MAF sensor.
- If you find a poor connection, replace the faulty terminal(s).
Refer to Body and Accessories/Wiring Systems.
Did you find a poor connection?
| --
|
Go to Step 21
|
Go to Step 18
|
14
|
- Check the MAF sensor signal circuit between the PCM and the MAF
sensor for the following:
- An open circuit
- A short to ground
- A short to the MAF sensor ground circuit.
- Repair the circuit if the MAF sensor signal circuit is open or
shorted.
Did you find the MAF sensor signal circuit open or shorted?
| --
|
Go to Step 21
|
Go to Step 20
|
15
| Locate and repair the open in the ground circuit to the MAF sensor. Refer
to Body and Accessories/Wiring Systems.
Is the action complete?
| --
|
Go to Step 21
| --
|
16
| Locate and repair
the open in the ignition feed circuit to the MAF sensor. Refer to Body and Accessories/Wiring Systems.
Is the action complete?
| --
|
Go to Step 21
| --
|
17
| Locate and repair
the short to voltage in the MAF sensor signal circuit. Refer to Body and Accessories/Wiring Systems.
Is the action complete?
| --
|
Go to Step 21
| --
|
18
| Replace the MAF sensor.
Refer to
Mass Air Flow (MAF) Sensor Replacement
.
Is the action complete?
| --
|
Go to Step 21
| --
|
19
| Replace the MAP sensor.
Refer to
Manifold Absolute Pressure (MAP) Sensor Replacement
.
Is the action complete?
| --
|
Go to Step 21
| --
|
20
|
Important:Program the replacement PCM. Refer to
PCM/TAC Module Replacement
.
Replace the PCM.
Is the action complete?
| --
|
Go to Step 21
| --
|
21
|
- Select the Diagnostic Trouble Code (DTC) option and the Clear
DTC Information option using the scan tool.
- Idle the engine at the normal operating temperature.
- Select the Diagnostic Trouble Code (DTC) option and the Specific
DTC option, then enter the DTC number using the scan tool.
- Operate the vehicle within the Conditions for Setting the DTC
as specified in the supporting text, if applicable.
Does the scan tool indicate that this test ran and passed?
| --
|
Go to Step 22
|
Go to Step 2
|
22
| Select the Capture Info option and the Review Info option using the scan tool.
Does the scan tool display any DTCs that you have not diagnosed?
| --
| Go to the applicable DTC table
| System OK
|
