Exhaust Gas Recirculation (EGR) System
The exhaust gas recirculation (EGR) system is used to reduce the amount of
nitrogen oxide (NOx) emission levels caused by combustion temperatures exceeding 816°C
(1,500°F). It does this by introducing small amounts of exhaust gas back into
the combustion chamber. The exhaust gas absorbs a portion of the thermal energy produced
by the combustion process and thus decreases combustion temperature. The EGR system
will only operate under specific temperature, barometric pressure and engine load
conditions in order to prevent driveability concerns and to increase engine performance.
Linear EGR Valve
The linear exhaust gas recirculation (EGR) valve consists of the following:
| • | The EGR valve position sensor |
| • | The EGR valve position sensor cap |
| • | The bobbin and coil assembly |
| • | The armature and base assembly |
| • | The exhaust gas inlet port |
| • | The exhaust gas outlet port |
Linear EGR Control
The linear exhaust gas recirculation (EGR) valve is controlled by a high side
driver within the powertrain control module (PCM). This high side driver uses a 12 volt
pulse width modulated (PWM) signal. The ground path for the EGR valve is completed
by turning on a separate driver within the PCM. The PCM calculates the amount of EGR
needed based on the following inputs:
| • | The engine coolant temperature (ECT) sensor |
| • | The intake air temperature (IAT) sensor |
| • | The barometric pressure (BARO) |
| • | The manifold absolute pressure (MAP) sensor |
| • | The throttle position (TP) sensor |
| • | The mass air flow (MAF) sensor |
EGR Diagnostics
The powertrain control module (PCM) tests the exhaust gas recirculation (EGR)
flow during deceleration by momentarily commanding the EGR valve to open while monitoring
the signal of the manifold absolute pressure (MAP) sensor. When the EGR valve is opened,
the PCM will expect to see a predetermined increase in MAP. If the expected increase
in MAP is not detected, the PCM records the amount of MAP difference that was detected
and adjusts a calibrated fail counter towards a calibrated fail threshold level. When
the fail counter exceeds the fail threshold level, the PCM will set a DTC.
Normally, the PCM will only allow one EGR Flow Test Count during an ignition
cycle. To aid in verifying a repair, the PCM allows 12 EGR Flow Test Counts
during the first ignition cycle following a code clear or a battery disconnect. Between
9-12 EGR Flow Test Counts should be sufficient for the PCM to determine
adequate EGR flow and pass the EGR flow test. If the PCM detects an EGR flow error,
a DTC will set.
The PCM monitors the position of the EGR valve pintle via the EGR position sensor.
If the PCM detects a calibrated variance between the Desired EGR Position parameter
and the EGR Position Sensor parameter, actual position, for a calibrated amount of
time, a DTC will set.
The PCM also monitors the EGR solenoid high control circuit EGR solenoid low
control circuit for electrical faults. If an EGR control circuit fault is detected
for a calibrated amount of time, a DTC will set.
