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Catalytic Converter Replacement
2012 Dodge Journey (2.4L DOHC 4-CYL World Engine)
The catalytic converter is the heart of the emissions control system. It prevents a significant percentage of hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx) emissions by converting unburned fuel into water vapor (H2O) and carbon dioxide (CO2). Also, NOx emissions are neutralized into nitrogen (N2) and oxygen (02). Without the catalytic converter, exhaust emissions would be a major problem. It goes without saying that a converter problem can dramatically increase tailpipe emissions and, possibly, prevent the vehicle from passing an emissions test.
Catalytic Converter Problems
As a general rule, a catalytic converter should remain operational for the life of the vehicle, but this is not always the case. If the converter becomes inoperable, it might be difficult to determine that it is. The performance of the vehicle might change, but it is likely that the driver won’t notice it.
The oxygen content in the catalytic converter is important for efficient conversion of exhaust gases. When a high oxygen content (lean) air/fuel ratio is present for an extended period, oxygen content in a catalyst can reach a maximum. When a rich air/fuel ratio is present for an extended period, the oxygen content in the catalyst can become totally depleted. When this occurs, the catalyst fails to convert the gases. This is known as catalyst punch through. This is not a converter problem. It is an engine performance problem that adversely affects the converter operation.
Catalyst operation is dependent on its ability to store and release the oxygen needed to complete the emissions-reducing chemical reactions. As a catalyst deteriorates, its ability to store oxygen is reduced. Since the catalyst’s ability to store oxygen is somewhat related to proper operation, oxygen storage can be used as an indicator of catalyst performance.
Unleaded gasoline must be used to avoid ruining the catalyst core. Do not allow the engine to operate above 1,200 RPM in neutral for extended periods over five minutes. This condition may result in excessive exhaust system/floor pan temperatures because of no air movement under the vehicle.
Perform an exhaust system inspection to rule out other issues besides the converter. Check the exhaust pipes, converter, muffler and resonators for cracked joints, broken welds and corrosion damage that would result in a leaking exhaust system. Inspect the clamps, support brackets and insulators for cracks and corrosion damage.
The combustion reaction caused by the catalyst releases additional heat in the exhaust system, causing temperature increases in the area of the reactor under severe operating conditions. Such conditions can exist when the engine misfires or otherwise does not operate at peak efficiency. This deterioration of the catalyst core can result in excessively high emission levels, noise complaints, and exhaust restrictions.
Problems with the converter can come to light when the vehicle undergoes an emissions system check, but only certain areas of the country still require such tests. If a converter performance problem is suspected, a catalyst related Diagnostic Trouble Code (DTC) might be set. If one is set, the MIL (malfunction indicator lamp) could be illuminated. The DTC that would be set is P0420, Catalyst System Efficiency Below Threshold Bank 1. Refer to the appropriate service manual for the procedures to determine if the setting of the DTC is the result of a bad converter, or another problem such as an aging upstream O2 sensor.
Replacing the Catalytic Converter
The degree of difficulty in replacing a catalytic converter depends entirely on the engine design and layout. Our subject vehicle for this article is the 2012 Dodge Journey with the 2.4L, DOHC 4 cylinder World Engine. This replacement procedure is rather straightforward.
Warning: The normal operating temperature of the exhaust system is very high; therefore, never work around or attempt to service any part of the exhaust system until it is cooled; special care should be taken when working near the catalytic converter; the temperature of the converter rises to a high level after a short period of engine operating time.
Refer to Figure 1. Raise and support the vehicle. Apply penetrating oil to the band clamp nut and bolt. Disconnect the oxygen sensor connector ①. Remove the oxygen upstream and downstream O2 sensors. Loosen the resonator and muffler assembly to the catalytic converter band clamp. Then, pull the muffler and resonator assembly rearward to remove it from the catalytic converter. Remove the flange nuts ② at the exhaust manifold and remove the catalytic converter from the vehicle ③. Remove and discard the gasket.
With the converter out of the vehicle and on the ground (see Figure 2), you can inspect it. Visually inspect the catalytic converter element by using a borescope or equivalent tool. Remove the oxygen sensor(s) and insert the borescope. If a borescope is not available, remove the converter and inspect the element using a flashlight. Inspect the element for cracked or melted substrate.
Note: On the PT Cruiser there is a block of foam under the bumper cover and between the license plate and back-up lamp. It might be necessary to first drill a large diameter hole through the foam in order to pull wires through.
Clean the manifold-to-converter sealing surfaces. Using a new gasket (see Figure 3), position the catalytic converter-to-exhaust manifold. Install the catalytic converter mounting bolts. Tighten to 20 ft.-lbs. (see Figure 4). Install the upstream and downstream O2 sensors. Position a new band clamp onto the resonator and muffler assembly, then install the resonator and muffler assembly onto the catalytic converter. Align the exhaust system to maintain position and proper clearance with the underbody parts. All support isolators should have equal load on them. Tighten the resonator and muffler assembly band clamp to 40 ft.-lbs. Lower the vehicle.
Start the engine and inspect the exhaust system for any leaks. Repair any exhaust leaks as necessary. Check the exhaust system for contact with the undercar body panels. Make any necessary adjustments as needed.