Circuit Description
The Mass Air Flow (MAF) sensor measures the amount of air entering the engine during a given time. The PCM uses the mass air flow information to monitor EGR flow rates. A large quantity of air entering the engine indicates an acceleration, high load situation or no EGR flow, while a small quantity of air indicates deceleration, idle or full EGR situations.
The PCM will monitor MAF and EGR pressures at different ranges to determine correct EGR flow rates. This is a type B DTC.
Conditions for Setting the DTC
| • | Five ALM Cells that are greater than 1.5. |
Action Taken When the DTC Sets
The PCM will shut down the EGR.
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL off after three consecutive trips without a fault condition. |
| • | A History DTC will clear when forty consecutive warm-up cycles that the diagnostic does not fail (coolant temperature has risen 5°C (40°F) from start up coolant temperature and engine coolant temperature exceeds 71°C (160°F) that same ignition cycle. |
| • | Use of a Scan tool |
Diagnostic Aids
The most likley cause of failure is a mechanical problem in the EGR value not allowing it to close.
To run the diagnostic test the engine must be at the operating temperature, vehicle in drive at idle for approximately 1 minute, then with the vehicle in park hold engine rpm steady between 1500 and 2100 rpm for 30 seconds. If the diagnostic test fails to run, vehicle must be driven.
The Adaptive Learn Matrix (ALM) is used to adjust the EGR vacuum control based on Mass Air Flow (MAF). The ALM may change as a result of back pressure increases over the life of the vehicle or other engine system variations. The ALM is made up of sixteen cells (numbered from zero to fifteen) in which each cell covers a range of engine speed (RPM) and load (mm3).
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 |
Important: Before clearing DTC(s) use the scan tool Capture Info to record freeze frame and failure records for reference, as data will be lost when Clear Info function is used. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||
2 | Are there any other EGR DTCs set? | -- | Go to the applicable DTC Table | |||||
Is action complete? | -- | -- | ||||||
4 |
Important: After repairs, the EGR ALM cells must be reset (under special function in scan tool). Are EGR ALM cells reset? | -- | -- | |||||
5 |
Does the Scan Tool indicate that this diagnostic Passed? | -- | ||||||
6 | Using the Scan Tool, select Capture Info, Review Info. Are any DTCs displayed that have not been diagnosed? | -- | Go to the Applicable DTC Table | System OK |
