GM Service Manual Online
For 1990-2009 cars only

Object Number: 185071  Size: LF
Engine Controls Components
EGR, MAF and Accelerator Pedal Controls
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

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.

Conditions for Running the DTC

    • The PCM performs this DTC diagnostic continuously.
    • Baro greater than 75 kPa.
    • The DTCs P0405, P0406, P0102 and P0103 are not set.

Conditions for Setting the DTC

    • Five ALM Cells that are less than 0.5.
    • All diagnostic set conditions met for 2 seconds.

Action Taken When the DTC Sets

    • The PCM will shut down the EGR.
    • The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.
    • The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the Failure Records will store this information. If the diagnostic reports a failure on the second consecutive drive trip, the Freeze Frame records the operating conditions at the time of failure and updates the Failure Records.

Conditions for Clearing the MIL/DTC

    • The PCM will turn the MIL off after three consecutive trips without a fault condition.
    • A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures
    • The use of a scan tool.

Diagnostic Aids

The most likely cause of failure is a mechanical problem in the EGR valve not allowing it to close.

To run the diagnostic test the engine must be at operating temperature, with the 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.

  1. If the EGR valve is at fault, excessive black smoke will be present.

Step

Action

Value(s)

Yes

No

1

Important: Before clearing any DTCs, use the scan tool Capture Info to save freeze frame and failure records for reference, as the Scan tool loses data when using the Clear Info function.

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Are there any other EGR DTCs set?

--

Go to the Applicable DTC Table

Go to Step 3

3

  1. Repair one of the following conditions:
  2. • Malfunctioning EGR valve (valve not remaining closed).
    • Restriction in exhaust system (high back pressure).
  3. Repair the problem as necessary.

Is the action complete?

--

Go to Step 4

--

4

Important: After repairs, the EGR ALM cells must be reset (under special function in scan tool).

Are the EGR ALM cells reset?

--

Go to Step 5

--

5

  1. Using the Scan tool, clear the DTCs.
  2. Start engine and idle at normal operating temperature.
  3. Select DTC, Specific, then enter the DTC number which was set.
  4. Operate vehicle until scan tool indicates the diagnostic Ran.

Does the Scan Tool indicate the diagnostic Passed?

--

Go to Step 6

Go to Step 2

6

Does the Scan tool display any additional undiagnosed DTCs?

--

Go to the Applicable DTC Table

System OK