Escape 2WD V6-3.0L (2009)
Catalytic Converter: Description and Operation
Catalyst and Exhaust Systems
Overview
The catalytic converter and exhaust systems work together to control the release of harmful engine exhaust emissions into the atmosphere. The engine
exhaust gas consists mainly of nitrogen (N), carbon dioxide (CO2) and water (H2O). However, it also contains carbon monoxide (CO), oxides of
nitrogen (NOx), hydrogen (H), and various unburned hydrocarbons (HCs). The major air pollutants of CO, NOx, and HCs, and their emission into the
atmosphere must be controlled.
The exhaust system generally consists of an exhaust manifold, front exhaust pipe, front heated oxygen sensor (HO2S), rear exhaust pipe, catalyst HO2S,
a muffler, and an exhaust tailpipe. The catalytic converter is typically installed between the front and rear exhaust pipes. On some vehicle applications,
more than one catalyst is used between the front and rear exhaust pipes. Catalytic converter efficiency is monitored by the on board diagnostic (OBD)
system strategy in the powertrain control module (PCM). For information on the OBD catalyst monitor, refer to the description for the Catalyst
Efficiency Monitor See: Powertrain Management/Computers and Control Systems/Testing and Inspection/Monitors, Trips, Drive Cycles and Readiness
Codes/Catalyst Efficiency Monitor.
For most vehicles, only two HO2Ss are used in an exhaust stream. The front sensors (HO2S11/HO2S21) before the catalyst are used for primary fuel
control while the ones after the catalyst (HO2S12/HO2S22) are used to monitor catalyst efficiency. However, some partial zero emission vehicles
(PZEVs) use three HO2Ss. The stream 1 sensor (HO2S11) located before the catalyst is used for primary fuel control, the stream 2 sensor (HO2S12) is
used to monitor the light-off catalyst, and the stream 3 sensor (HO2S13) located after the catalyst is used for long term fuel trim control to optimize
catalyst efficiency (fore aft oxygen sensor control).
V-Engines
V-Engines
In-Line Engines
In-Line Engines
Catalytic Converter
A catalyst is a material that remains unchanged when it initiates and increases the speed of a chemical reaction. A catalyst also enables a chemical
reaction to occur at a lower temperature. The concentration of exhaust gas products released to the atmosphere must be controlled. The catalytic
converter assists in this task. It contains a catalyst in the form of a specially treated ceramic honeycomb structure saturated with catalytically active
precious metals. As the exhaust gases come in contact with the catalyst, they are changed into mostly harmless products. The catalyst initiates and speeds
up heat producing chemical reactions of the exhaust gas components so they are used up as much as possible.
Light Off Catalyst
As the catalyst heats up, converter efficiency rises rapidly. The point at which conversion efficiency exceeds 50% is called catalyst light off. For most
catalysts this point occurs at 246°C to 302°C (475°F to 575°F). A fast light catalyst is a three way catalytic converter (TWC) that is located as close to
the exhaust manifold as possible. Because the light off catalyst is located close to the exhaust manifold it lights off faster and reduces emissions more
quickly than the catalyst located under the body. Once the catalyst lights off, the catalyst quickly reaches the maximum conversion efficiency for that
