EGR Enable/Disable Conditions

EGR Valve Control Schematic:

Enable/Disable Conditions
All of the following conditions must be met before the PCM will allow EGR operation to begin:

1. Engine running.

2. PCM in ignition control mode.

3. Transaxle in drive range.

4. Intake air temperature between -10°C and 128°C.

5. a) If Engine Coolant Temperature (ECT) was between 18°C and 36°C at engine start-up, ECT must be between 18°C and 115°C.

b) If engine coolant temperature (ECT was less than 18°C or greater than 36°C at engine start-up, ECT must be between 80°C and 115°C.

6. Manifold air pressure must be greater than a low limit, between 25 and 34 kPa depending on barometric pressure, and less than 90 kPa.

7. Engine speed between 800 and 3200 RPM.

8. Throttle position must be less than a high limit, between 19 degrees and 35 degrees depending on barometric pressure.

9. Any one of the following conditions met:

^ Vehicle speed less than 36 MPH and throttle position switch open.

^ Vehicle speed less than 36 MPH, throttle switch closed.

^ Vehicle speed 2 MPH or less and throttle position at least 1.4 degrees.

10. Fuel is not being disabled to any cylinder due to traction control or acceleration reduction.

11. No engine overtemperature condition is present.

12. If all of the EGR enable conditions have been met but the PCM determines that A/C clutch engagement is impending, EGR enable will be delayed until 0.15 second after the A/C clutch engages.

Closed Valve Pintle Position
At key-on, the PCM sets the closed valve pintle position to 103 counts. Since the EGR valve pintle will not close to 0 counts, the PCM uses 103 counts as a reference point. The closed valve pintle position is updated only when the actual pintle position falls below 103 counts. If the closed valve pintle position is measured above 103 counts, the PCM will set a diagnostic trouble code. A DTC will also set if the pintle position falls below 9 counts. Closed valve pintle positions outside of this range indicate a pintle position sensor failure. Once the closed valve pintle position is established, the PCM uses this information to calculate the normalized pintle position.

Normalized Pintle Position
After the closed valve pintle position is established, the PCM calculates a normalized pintle position. The normalized position is the difference between the actual pintle position and the closed valve pintle position multiplied by a scaling factor. The PCM uses the normalized pintle position to determine the desired pintle position for maximum EGR performance.

Desired Pintle Position
The desired pintle position is the result of computations performed by the PCM using various inputs such as engine speed, intake manifold temperature and pressure, air flow, and engine coolant temperature, and stored calibrations from the PCM EPROM. By continuously computing the desired pintle position, the PCM can vary EGR flow for particular driving conditions.

The PCM calculates pintle position error, desired pintle position minus normalized pintle position, to determine if it is accurately controlling EGR flow. If the pintle position error exceeds 25 counts for more than 10 seconds, the PCM will set a diagnostic trouble code.

Turning EGR On and Off
When all of the conditions have been met to enable EGR, the PCM calculates the desired pintle position and determines the rate at which it will open or ramp the pintle to its desired position. The ramp rate depends on vehicle speed, A/C clutch status, and outside air temperature. The PCM controls the ramp rate by varying the EGR solenoid duty cycle. The ramp rate is a percentage of desired pintle position and is determined as follows:

^ If the vehicle speed is greater than 20 MPH, the pintle will open at a rate of 5% every 0.05 second.

^ If the vehicle speed is less than or equal to 20 MPH, A/C clutch engagement is not possible, and outside air temperature is at least 41°F, the pintle will open at a rate of 2.3% every 0.05 second.

^ If the vehicle speed is less than or equal to 20 MPH, A/C clutch engagement is possible or outside air temperature is less than 4°F, the pintle will open at a rate of 0.8% every 0.05 second.

The PCM will maintain the same ramp rate until the desired pintle position is reached. When EGR is being ramped on, the PCM will maintain current spark advance. The PCM will ramp the spark to its desired advance once EGR has reached its desired position. This delay is necessary because EGR does not reach all cylinders immediately, and premature spark advance would cause driveability problems.

When EGR is turned off, the PCM will cause the pintle to close at a rate of 6.3% every 0.05 second until the pintle is in the closed position. However, if engine speed is 0 RPM (engine not running), the pintle will be immediately closed.

If EGR status transitions from off to on or on to off during a ramp, the ramp will reverse directions from that point and continue at the normal rate until the desired pintle position is reached.