Description

Air Mass Flow Meter Description

1. Fault Codes:
Mass Air Flow Circuit - Low Input P0102
Mass Air Flow Circuit - High Input P0103
Mass Air Flow Circuit Range / Performance Problem P0101

2. Monitoring Procedure

Summary
Faults with the airflow meter will be detected using three tests. A low range check will look for out of range values. Faults will be detected if the following circumstances are present, no signal (open circuit) at any time with the engine running, or high signal output below a given engine speed. An additional low signal check is performed with the throttle angle and engine speed above threshold values.

Low Range Check
The average value of airflow meter volts is compared to lower limits (AIRFLOW DIAG AFM MIN VOLTAGE) when the engine is running. If the voltage is less than this limit then a counter is incremented, otherwise it is decremented. If the counter reaches a threshold limit, then a fault is present.

High Signal Check
The average value of airflow meter volts is compared to an upper limit (AIRFLOW DIAG AFM MAX VOLTAGE) when the engine speed below a threshold (AIRFLOW DIAG AFM TEST SPEED). If the voltage is greater than this limit then a counter is incremented, otherwise it is decremented. If the counter reaches a threshold limit, then a fault is present.

Low Signal Check
A low signal test will check for an air meter output consistent with other engine parameters.
If the airflow meter gives a low signal when both throttle angle and engine speed are above thresholds (AIRFLOW DIAG THANG THRESH & AIRFLOW DIAG SPEED THRESH respectively), then a fault is present.
If the tests are not passed then the appropriate fault counter, (AIRFLOW DIAG FAULT LIMIT), will be incremented, otherwise it will be decremented.
If the count exceeds a given threshold then a fault is present.

3. Primary Detection Parameter
Airflow meter signal voltage - measured at the ECM input.

4. Fault Criteria Limits
Airflow meter - Low out of range 350mV
Airflow meter - High rationality limit 4.5V
Airflow meter - Low rationality limit 1.1V

5. Monitoring Conditions
The low range check will take place whenever the engine is running; the high signal check will take place when the engine speed is below a given threshold. The low signal check occurs when the throttle angle and engine speed are above respective thresholds.
AIRFLOW DIAG AFM TEST SPEED, the maximum engine speed for the high signal check, 1000 rpm.
AIRFLOW DIAG THANG THRESH, the absolute throttle potentiometer volts, must be above 2.5V.
AIRFLOW DIAG SPEED THRESH, the minimum engine speed for the low signal test, 1500 rpm.
AIRFLOW DIAG FAULT LIMIT, the amount of fault events required to flag a fault, 40.
The Low Signal Check is inhibited whenever there is a fault present with the throttle position input.

6. Monitoring Time Length / Frequency of Checks
The frequency of the Airflow meter Diagnostic is 10Hz, throughout all engine-operating conditions.

7. Criteria for Storing Fault Code
Two successive trips where the airflow meter diagnostic indicates a failed airflow meter.

8. Criteria for Illuminating MIL
Two successive trips where the airflow meter diagnostic indicates a failed airflow meter.

9. Criteria for Determining Out of Range Input Signals
The airflow meter voltage is range tested as described above. Engine speed signal is checked for correct number of teeth on wheel between missing teeth. Throttle Angle input is subject to maximum & minimum range checks.