Joined: 26 Oct 2004
|Posted: Fri Nov 12, 2004 8:00 am Post subject: DTC P0420 Catalyst System Low Efficiency Bank 1
DTC P0420 Catalyst System Low Efficiency Bank 1
In order to maintain a reasonably low emissions of Hydrocarbons (HC),
Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), the engine controls system
uses a three-way catalytic converter. The catalyst within the
converter promotes a chemical reaction which oxidizes the HC
and CO present in the exhaust gas. This reaction converts them
into harmless water vapor and Carbon Dioxide. The catalyst also
reduces NOx, converting it to Nitrogen. The PCM monitors this
process using Bank 1 HO2S #2. Bank 1 HO2S #2, located in the
exhaust stream past the three-way catalytic converter, produces
an output signal which indicates the oxygen storage capacity
of the catalyst. This determines the catalysts ability to convert
exhaust emissions effectively. If the catalyst is functioning
correctly, the Bank 1 HO2S #2 signal will be far less active
than that produced by Bank 1 HO2S #1. This indicates that the
three-way catalytic converters oxygen storage capacity is below
a threshold considered acceptable.
When the conditions for running this DTC are met, the following occurs:
- The PCM captures the current rear HO2S rich/lean status.
- The Air Fuel ratio transitions from rich to lean or lean to rich
depending on the capture rear HO2S rich/lean status.
- The Air Fuel ratio transitions a second time opposite the first
Air Fuel ratio transition.
- The PCM captures the response time (the time the HO2S goes from
below 300 mV to above 600 mV and from 600 mV to below
300 mV) of the front and rear Heated Oxygen sensors when
the Air Fuel ratio transitions occurred.
- The PCM measures the time it takes the rear HO2S voltage to cross
a reference rich/lean threshold minus the time it takes the front HO2S voltage
to cross the same rich/lean threshold. The time difference from
the front and rear HO2S is the oxygen storage capacity of the catalyst.
This DTC sets if the time exceeds a predetermined threshold.
Conditions for Running the DTC
- DTCs, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117,
P0118, P0121, P0122, P0123, P0125, P0171, P0172, P0174, P0175, P0200, P0230,
P0300, P0325, P0327, P0332, P0335, P0336, P0341, P0342, P0343, P0351-P0358,
P0401, P0404, P0405, P0410, P0412, P0418, P0440, P0442, P0443, P0446,
P0449, P0500, P0704, P0801, P0803, P1258, P1336, P1404, P1415, P1416,
P1441 and HO2S DTCs not set.
- The engine is operating for longer than 400 seconds.
- The ECT is between 80°C (176°F) 120°C (248°F).
- The IAT is between -15°C (5°F) and 75°C (167°F).
- Engine speed is more than 900 RPM for a minimum of 22 seconds
(manual transmission) or 25 seconds (Automatic Transmission) since
the end of the last idle test.
- The BARO is more than 74 kPA.
- The fuel system is operating in closed loop.
Conditions for Setting the DTC
The PCM determines the oxygen storage capability of the catalytic converter
has degraded below a calibrated threshold.
Action Taken When the DTC Sets
- The PCM illuminates the malfunction indicator lamp (MIL) when
the diagnostic runs and fails.
- The PCM records the operating conditions at the time the diagnostic
fails. The PCM stores this information in the Freeze Frame and/or Failure
Conditions for Clearing the MIL/DTC
- The PCM turns OFF the malfunction indicator lamp (MIL) after
3 consecutive ignition cycles that the diagnostic runs and does not
- A last test failed, or current DTC, clears when the diagnostic
runs and does not fail.
- A history DTC clears after 40 consecutive warm-up cycles,
if no failures are reported by this or any other emission related diagnostic.
- Use a scan tool in order to clear the MIL and the DTC.
If the HO2S parameter is monitored using a scan tool while this diagnostic
is running, the HO2S voltages may be fixed low or high.
The numbers below refer to the step numbers on the diagnostic table.
Before replacing the Three-Way Catalytic Converter, correct any conditions
which may have damaged the catalyst.
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?
Go to Step 2
Powertrain On Board Diagnostic (OBD) System Check
Are any other DTCs
Go to the applicable DTC table
Go to Step
Inspect for the following conditions:
- Verify that the three-way catalytic converter is an original equipment
- Inspect the three-way catalytic converter for damage (dents, severe
discoloration caused by excessive temperature, holes, etc.).
- Insure that the internal three-way catalytic converter rattle
caused by damaged catalyst is not present.
- Inspect the exhaust system for leaks, damage, or loose or missing
hardware (area from converter to HO2S #2 primarily). Refer to
Exhaust System Inspection
in Engine Exhaust.
- Insure that the HO2S #1 and the HO2S #2 are secure and that the
pigtails and wiring are not damaged or contacting the exhaust.
Did you find and correct the condition?
Go to Step 5
Go to Step 4
Replace the catalytic converter. Refer to
Oxidation Catalytic Converter Replacement
in Engine Exhaust.
Is the action complete?
Go to Step
- Select the Diagnostic Trouble Code (DTC) option and the Clear
DTC Information option using the scan tool.
- Idle the engine at the normal operating temperature.
- Select the Diagnostic Trouble Code (DTC) option and the Specific
DTC option, then enter the DTC number using the scan tool.
- Operate the vehicle within the Conditions for Running the DTC
as specified in the supporting text, if applicable.
Does the scan tool indicate that this test ran and passed?
Go to Step 6
Go to Step
Select the Capture Info option and the Review Info option using the
Does the scan tool display any DTCs that you have not diagnosed?
Go to the applicable
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