RAM 2500 Truck 2WD V8-5.2L VIN Y (2000)
Oxygen Sensor Relay: Description and Operation
Oxygen Sensor Heaters/Heater Relays: Depending on the emissions package, the heating elements within the sensors will be supplied voltage from either
the ASD relay, or 2 separate oxygen sensor relays Refer to Wiring Diagrams to determine which relays are used. See: Relays and Modules - Power and
Ground Distribution/Relay Box
The 02 sensor uses a Positive Thermal Co-efficient (PTC) heater element. As temperature increases, resistance increases. At ambient temperatures
around 70°F, the resistance of the heating element is approximately 4.5 ohms. As the sensor temperature increases, resistance in the heater element
increases. This allows the heater to maintain the optimum operating temperature of approximately 930° - 1000° (500°- 600°C) Although the sensors
operate the same, there are physical differences, due to the environment that they operate in, that keep them from being interchangeable
Maintaining correct sensor temperature at all times allows the system to enter into closed loop operation sooner. Also, it allows the system to remain in
closed loop operation during periods of extended idle.
In Closed Loop operation, the PCM monitors certain 02 sensor input(s) along with other inputs, and adjusts the injector pulse width accordingly. During
Open Loop operation, the PCM ignores the 02 sensor input. The PCM adjusts injector pulse width based on preprogrammed (fixed) values and inputs
from other sensors.
Upstream Sensor (Non-California Emissions): The upstream sensor (1/1) provides an input voltage to the PCM. The input tells the PCM the oxygen
content of the exhaust gas. The PCM uses this information to fine tune fuel delivery to maintain the correct oxygen content at the downstream oxygen
sensor. The PCM will change the air/fuel ratio until the upstream sensor inputs a voltage that the PCM has determined will make the downstream sensor
output (oxygen content) correct.
The upstream oxygen sensor also provides an input to determine catalytic convertor efficiency
Downstream Sensor (Non-California
Emissions): The downstream oxygen sensor (1/2) is also used to determine the correct air-fuel ratio. As the oxygen content changes
at the downstream sensor, the PCM calculates how much air-fuel ratio change is required. The PCM then looks at the upstream oxygen sensor voltage
and changes fuel delivery until the upstream sensor voltage changes enough to correct the downstream sensor voltage (oxygen content)
The downstream oxygen sensor also provides an input to determine catalytic convertor efficiency.
Upstream Sensors (California Emissions):
Two upstream sensors are used (1/1 and 2/1) The 1/1 sensor is the first sensor to receive exhaust gases from the #1 cylinder. They provide an input
voltage to the PCM. The input tells the PCM the oxygen content of the exhaust gas~ The PCM uses this information to fine tune fuel delivery to maintain
the correct oxygen content at the downstream oxygen sensors. The PCM will change the air/fuel ratio until the upstream sensors input a voltage that the
PCM has determined will make the downstream sensors output (oxygen content) correct.
The upstream oxygen sensors also provide an input to determine mini-catalyst efficiency. Main catalytic convertor efficiency is not calculated with this
package.
Downstream Sensors (California
Emissions): Two downstream sensors are used (1/2 and 2/2) The downstream sensors are used to determine the correct air-fuel ratio. As the oxygen
content changes at the downstream sensor, the PCM calculates how much air- fuel ratio change is required. The PCM then looks at the upstream oxygen
sensor voltage, and changes fuel delivery until the upstream sensor voltage changes enough to correct the downstream sensor voltage (oxygen content)
The downstream oxygen sensors also provide an input to determine mini-catalyst efficiency. Main catalytic convertor efficiency is not calculated with
this package.
Medium and Heavy Duty 8.OL V-10 Engine:
Four oxygen sensors are used (2 upstream, 1 pre-catalyst and 1 post-catalyst) The upstream sensors (1/1 and 2/1) will fine-tune the air-fuel ratio through
the Powertrain Control Module (PCM) The pre- catalyst (1/2) and post-catalyst (1/3) sensors will determine catalytic convertor efficiency (efficiency of
the main catalytic convertor) This is also done through the PCM.
Heavy Duty 5.9L Engine:
Downstream sensors are not used with this emissions package, meaning catalytic convertor efficiency is not calculated with this package.
Two upstream sensors are used. The left upstream sensor (1/1) will monitor cylinders 1, 3, 5 and 7 The right upstream sensor (2/1) will monitor cylinders
2, 4, 6 and 8. The PCM monitors the oxygen content of the sensors, and will fine-tune the air-fuel ratio.
Engines equipped with either a downstream sensor(s), or a post-catalytic sensor, will monitor catalytic convertor efficiency. If efficiency is below
emission standards, the Malfunction Indicator Lamp (MIL) will be illuminated and a Diagnostic Trouble Code (DTC) will be set. Refer to Monitored
Systems in Emission Control Systems for additional information See: Powertrain Management/Computers and Control Systems/Testing and
Inspection/Monitors, Trips, Drive Cycles and Readiness Codes
