DTC P0420 (LDD)
Diagnostic Instructions
DTC Descriptor
| DTC P0420 00: Catalyst System Low
Efficiency |
Circuit/System Description
Note: A new catalyst with
less than 160 km (100 mi) on it may set DTC P0420 00 due to
outgassing of the internal matting. Operating the vehicle at
highway speeds for approximately 1 h may correct the condition.
A 3-way catalyst controls emissions of hydrocarbons, carbon
monoxide (CO), and oxides of nitrogen (NOX). The catalyst within
the converter promotes a chemical reaction, which oxidizes the
hydrocarbon(s) and the CO that are present in the exhaust gas. This
process converts the hydrocarbon(s) and the CO into water vapor and
carbon dioxide (CO2), and reduces the NOX, converting the NOX into
nitrogen. The catalyst also stores oxygen. The engine control
module (ECM) monitors this process by using a heated oxygen sensor
(HO2S) that is in the exhaust stream after the 3-way catalyst. The
HO2S 2 produces an output signal that the ECM uses to calculate the
oxygen storage capacity of the catalyst. This indicates the ability
of the catalyst to convert the exhaust emissions efficiently. The
ECM monitors the efficiency of the catalyst by allowing the
catalyst to heat, then wait for a stabilization period while the
engine is idling. The ECM then adds and removes fuel while
monitoring the HO2S 2. When the catalyst is functioning properly,
the HO2S 2 response to the extra fuel is slow compared to the
response of the HO2S 1, which is located before the 3-way catalyst.
When the HO2S 2 response is near that of the HO2S 1, the oxygen
storage capability and efficiency of the catalyst may be degraded
below an acceptable threshold.
Conditions for Running the DTC
| • |
DTCs P0016 00, P0017 00, P0030
00, P0036 00, P0053 00, P0054 00, P0101 00, P0102 00, P0103 00,
P0112 00, P0113 00, P0114 00, P0117 00, P0118 00, P0121 00, P0122
00, P0123 00, P0131 00, P0132 00, P0133 00, P0134 00, P013 00,
P0137 00, P0138 00, P0140 00, P0141 00, P0171 00, P0172 00, P0300
00, P0301 00, P0302 00, P0303 00, P0304 00, P0335 00, P0336 00,
P0340 00, P0365 00, P0443 00, P0502 00, P0506 00, P0507 00, P1133
00, and P2135 00 are not set. |
| • |
Before the ECM performs the
idle test, the vehicle must be driven under the following
conditions: |
| |
- |
The engine speed
is greater than 975 RPM. |
| |
- |
The engine run
time is greater than a calibrated value. |
| |
- |
Both conditions
exist for greater than 15 s. |
| • |
The throttle is in the rest
position. |
| • |
The evaporative emission
(EVAP) purge concentration is learned. |
| • |
The short term fuel trim is
learned. |
| • |
The air flow into the engine
is between 1-10 g/s. |
| • |
The engine has been idling
less than 50 s. |
| • |
The vehicle speed is less than
2 km/h (1 MPH). |
| • |
The engine coolant temperature
(ECT) is between 46-140°C (115-284°F). |
| • |
The intake air temperature
(IAT) is between -20 to +250°C (-4 to +482°F). |
| • |
The barometric pressure (BARO)
is greater than 70 kPa. |
| • |
The catalyst calculated
temperature is less than 900°C (1 652°F). |
| • |
The engine is operating in
closed loop. |
| • |
Torque fuel reduction is not
active. |
| • |
The transmission is not in P/N
(automatic transmission only). |
| • |
This diagnostic attempts one
test during each valid idle period once the above conditions have
been met. This diagnostic attempts up to 12 tests during each drive
cycle. |
Conditions for Setting the DTC
The ECM determines that the efficiency of the catalyst has
degraded below a calibrated threshold.
Action Taken When the DTC Sets
DTC P0420 00 is a Type A DTC.
Conditions for Clearing the DTC
DTC P0420 00 is a Type A DTC.
Diagnostic Aids
Inspect for the following conditions, which may cause a catalyst
to degrade:
| • |
High engine oil or high
coolant consumption |
| • |
A damaged oxygen sensor or
wiring harness |
Reference Information
Schematic Reference
Engine Controls Schematics
Connector End View Reference
Component Connector End Views
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Testing
| 1. |
Engine idling, observe the DTC
information with a scan tool. Verify there are no HO2S or misfire
DTCs set. |
| 2. |
Verify the following
conditions do not exist with the catalyst: |
| |
• |
A severe discoloration caused
by excessive temperatures |
| |
• |
An internal rattle caused by
damaged catalyst subset |
| ⇒ |
If a condition is found, replace the catalyst. |
| 3. |
Verify the following
conditions do not exist with the exhaust system: |
| |
• |
Loose or missing
hardware |
| |
• |
Properly torqued B52A Heated
Oxygen Sensor 1 or B52B Heated Oxygen Sensor 2 |
| ⇒ |
If a condition is found, repair the exhaust
system. |
| ⇒ |
If the DTC fails this key cycle, continue with
this procedure. |
| 4. |
Verify the following
conditions do not exist with the B52B Heated Oxygen Sensor
2. |
| |
• |
A grounded B52B Heated Oxygen
Sensor 2 wiring harness |
| ⇒ |
If a condition is found, replace the B52B Heated Oxygen Sensor
2. |
| 5. |
If no physical condition is
detected and the B52B Heated Oxygen Sensor 2 is as active as the
B52A Heated Oxygen Sensor 1 after operating the engine at 1 500 RPM
for 1 min and then returning to a stabilized idle, then replace the
catalyst . |
Repair Instructions
Note: A new catalyst with
less than 160 km (100 mi) on it may set DTC P0420 00 due to
outgassing of the internal matting. Operating the vehicle at
highway speeds for approximately 1 h may correct the condition.
Perform the
Diagnostic Repair Verification after completing the diagnostic
procedure.
|
