DTC Advanced Diagnostics: P0420 (3.0L Engine)
DTC P0420: Catalyst System Efficiency Below Threshold
General Description
The three way catalytic converter (TWC) is monitored by the signals of air/fuel ratio (A/F) sensor (sensor 1) and secondary heated oxygen sensor (secondary HO2S (sensor 2)). The powertrain control module (PCM) calculates the sum of the absolute differences of A/F sensor (sensor 1) signals at regular intervals, and at the same time, calculates the sum of the absolute differences of the secondary HO2S (sensor 2) signals at regular intervals. If the ratio of each absolute difference summation of the A/F sensor (sensor 1) and the secondary HO2S (sensor 2) is a certain value, the PCM detects a malfunction and stores a DTC.
Monitor Execution, Sequence, Duration, DTC Type
| Execution | Once per driving cycle |
| Sequence | None |
| Duration | 22 seconds or more |
| DTC Type | Two drive cycles, MIL on |
Enable Conditions
| Condition | Minimum | Maximum |
|---|---|---|
| Engine coolant temperature [ECT Sensor 1] | 144 deg.F (60 deg.C) | - |
| MAF value [MAF Sensor] | 10 g/s (0.36 oz/s) | 60 g/s (2.11 oz/s) |
| MAF value change per 50 milliseconds | - | 17 g/s (0.59 oz/s) |
| Warm-up counter* | 8, 000 counts | - |
| Fuel feedback | Closed loop at stoichiometric | |
*: Counts up when MAF value is in the ranges of enable condition in other than during fuel cut-off.[ ]: HDS Parameter
Malfunction Threshold
The value derived by the following formula is more than 7.
Sum of the absolute differences of secondary HO2S (sensor 2) signals at regular intervals / (divide) sum of the absolute differences of A/F sensor (sensor 1) signals at regular intervals
Possible Cause
- TWC failure
- Rear A/F sensor (bank 1, sensor 1) failure
- Front A/F sensor (bank 2, sensor 1) failure
- Secondary HO2S (sensor 2) failure
Confirmation Procedure
Operating Condition
- Start the engine. Hold the engine speed [Engine Speed] at 3, 000 rpm without load (in P or N) until the radiator fan comes on.
- Drive the vehicle at a speed between 45 - 75 mph (70 - 120 km/h) for at least 5 minutes, to warm up the TWC.
- Drive at a steady speed between 55 - 75 mph (90 - 120 km/h) for at least 10 seconds.
- Decelerate with the throttle valve fully closed.
- Repeat Driving Pattern steps 3 through 4, four times.
- Set a vehicle speed [Vehicle Speed] of 55 mph (90 km/h) on the cruise control or equivalent, and drive for at least 67 seconds.
- After disconnecting the 12 volt battery, extend Driving Pattern step 6 to 4 minutes or longer.
- Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.
Diagnosis Details
Conditions for setting the DTC
When a malfunction is detected during the first drive cycle, a Pending DTC is stored in the PCM memory. If the malfunction returns in the next (second) drive cycle, the MIL comes on and a Confirmed DTC, the freeze data, and the on-board snapshot are stored.
Conditions for clearing the DTC
The MIL is cleared if the malfunction does not return in three consecutive trips in which the diagnostic runs. The MIL, the Pending DTC, the Confirmed DTC, the freeze data, and the on-board snapshot can be cleared with the scan tool clear command.