Grand Caravan V6-3.3L VIN R (2005)
EGR Valve: Description and Operation
MONITORED SYSTEMS
There are new electronic circuit monitors that check fuel, emission, engine and ignition performance. These monitors use information from various
sensor circuits to indicate the overall operation of the fuel, engine, ignition and emission systems and thus the emissions performance of the vehicle.
The fuel, engine, ignition and emission systems monitors do not indicate a specific component problem. They do indicate that there is an implied
problem within one of the systems and that a specific problem must be diagnosed.
If any of these monitors detect a problem affecting vehicle emissions, the Malfunction Indicator (Check Engine) Lamp will be illuminated. These
monitors generate Diagnostic Trouble Codes that can be displayed with the a scan tool.
The following is a list of the system monitors:
EGR Monitor (if equipped)
Misfire Monitor
Fuel System Monitor
Oxygen Sensor Monitor
Oxygen Sensor Heater Monitor
Catalyst Monitor
Evaporative System Leak Detection Monitor (if equipped)
Following is a description of each system monitor, and its DTC.
Refer to the appropriate Powertrain Diagnostics Procedures manual for diagnostic procedures.
OXYGEN SENSOR (O2S) MONITOR
Effective control of exhaust emissions is achieved by an oxygen feedback system. The most important element of the feedback system is the O2S. The
O2S is located in the exhaust path. Once it reaches operating temperatures of 300° to 350°C (572° to 662°F), the sensor generates a voltage that is
inversely proportional to the amount of oxygen in the exhaust. The information obtained by the sensor is used to calculate the fuel injector pulse
width. The PCM is programmed to maintain the optimum air/fuel ratio. At this mixture ratio, the catalyst works best to remove hydrocarbons (HC),
carbon monoxide (CO) and nitrous oxide (NOx) from the exhaust.
The O2S is also the main sensing element for the EGR (if equipped), Catalyst and Fuel Monitors.
The O2S may fail in any or all of the following manners:
Slow response rate
Reduced output voltage
Dynamic shift
Shorted or open circuits
Response rate is the time required for the sensor to switch from lean to rich once it is exposed to a richer than optimum A/F mixture or vice versa. As
the sensor starts malfunctioning, it could take longer to detect the changes in the oxygen content of the exhaust gas.
The output voltage of the O2S ranges from 0 to 1 volt (voltages are offset by 2.5 volts on NGC vehicles). A good sensor can easily generate any
output voltage in this range as it is exposed to different concentrations of oxygen. To detect a shift in the A/F mixture (lean or rich), the output voltage
has to change beyond a threshold value. A malfunctioning sensor could have difficulty changing beyond the threshold value.
OXYGEN SENSOR HEATER MONITOR
If there is an oxygen sensor (O2S) DTC as well as a O2S heater DTC, the O2S heater fault MUST be repaired first. After the O2S fault is repaired,
verify that the heater circuit is operating correctly.
Effective control of exhaust emissions is achieved by an oxygen feedback system. The most important element of the feedback system is the O2S. The
O2S is located in the exhaust path. Once it reaches operating temperatures of 300° to 350°C (572 ° to 662°F), the sensor generates a voltage that is
inversely proportional to the amount of oxygen in the exhaust. The information obtained by the sensor is used to calculate the fuel injector pulse
width. This maintains a 14.7 to 1 Air Fuel (A/F) ratio. At this mixture ratio, the catalyst works best to remove hydrocarbons (HC), carbon monoxide
(CO) and nitrogen oxide (NOx) from the exhaust.
The voltage readings taken from the O2S are very temperature sensitive. The readings are not accurate below 300°C (572 °F) Heating of the O2S is
done to allow the engine controller to shift to closed loop control as soon as possible. The heating element used to heat the O2S must be tested to
ensure that it is heating the sensor properly.
The O2S circuit is monitored for a drop in voltage. The sensor output is used to test the heater by isolating the effect of the heater element on the O2S
