Page 624 of 1943
DI±16
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)P0340
(DI±76)
Camshaft Position Sensor Cir-
cuit Malfunction
Open or short in camshaft position sensor circuit
Camshaft position sensor
Camshaft timing pulley
ECM
P0420
(DI±78)Catalyst System Efficiency Be-
low Threshold (Bank 1)
Gas leakage on exhaust system
Open or short in heated oxygen sensor circuit
Heated oxygen sensor
Three±way catalytic converter
P0440
(DI±81)Evaporative Emission Control
System Malfunction
Hose or tube cracked, hole, damaged or loose seal
Fuel tank cap incorrectly installed
Fuel tank cap cracked or damaged
Vacuum hose cracked, hole, blocked,damaged or discon-
nected
Fuel tank cracked, hole or damaged
Charcoal canister cracked, hole or damaged
Open or short in vapor pressure sensor circuit
Vapor pressure sensor
Fuel tank over fill check valve cracked or damaged
ECM
P0441
(DI±87)Evaporative Emission Control
System Incorrect Purge Flow
Vacuum hose cracked, hole, blocked damaged or discon-
nected
Open or short in vapor pressure sensor circuit
Vapor pressure sensor
Open or short in VSV circuit for EVAP
VSV for EVAP
P0446
(DI±87)Evaporative Emission Control
System Vent Control Malfunction
VSV for EVAP
Open or short in VSV circuit for vapor pressure sensor
VSV for vapor pressure sensor
Charcoal canister cracked, hole or damaged
Fuel tank over fill check valve cracked or damaged
ECM
P0450
(DI±103)Evaporative Emission Control
System Pressure Sensor Mal-
function
Open or short in vapor pressure sensor circuit
V
P0451
(DI±103)Evaporative Emission Control
System Pressure Sensor Range/
PerformanceVapor pressure sensor
ECM
P0500
(DI±105)Vehicle Speed Sensor Malfunc-
tion
Combination meter
Open or short in vehicle speed sensor circuit
Vehicle speed sensor
ECM
P0505
(DI±107)Idle Control System MalfunctionErectric throttle control system
Air induction system
*1: MIL lights up
Page 681 of 1943
FI7081
Waveform of Heated Oxygen
Sensor before CatalystNormal CatalystWaveform of Heated Oxygen
Sensor behind Catalyst
FI7132
Vehicle Speed
0
IG SW OFF
Warmed upWarmed upCheck
Time (a)(c)
(d)
Idling (b) 89 km/h (55 mph)
5 min. or more DI±78
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)
DTC P0420 Catalyst System Efficiency Below Threshold
CIRCUIT DESCRIPTION
The ECM compares the waveform of the oxygen sensor located before the catalyst with the waveform of
the oxygen sensor located behind the catalyst to determine whether or not catalyst performance has deterio-
rated.
Air±fuel ratio feedback compensation keeps the waveform of the oxygen sensor before the catalyst repeat-
edly changing back and forth from rich to lean.
If the catalyst is functioning normally, the waveform of the oxygen sensor behind the catalyst switches back
and forth between rich and lean much more slowly than the waveform of the oxygen sensor before the cata-
lyst.
But when both waveforms change at a similar rate, it indicates that catalyst performance has deteriorated.
DTC No.DTC Detecting ConditionTrouble Area
P0420
After the engine and the catalyst are warmed up, and while the
vehicle is driven within the set vehicle and engine speed range,
the waveforms of the oxygen sensors (bank 1 sensor 1 and
bank 1 sensor 2) have the same amplitude
(2 times detection logic)Gas leakage on exhaust system
Open or short in heated oxygen sensor circuit
Heated oxygen sensor
Three±way catalytic converter
CONFIRMATION DRIVING PATTERN
(a) Connect the TOYOTA hand±held tester to the DLC3, or connect the probe of the oscilloscope between
terminals OX1, OX2 and E1 of the ECM connector.
(b) Start engine and warm it up with all accessories switched OFF until water temp. is stable.
DI6VC±02
Page 682 of 1943
A14462
OX Signal Waveform (Oscilloscope)
500 msec./DivisionOX1
OX2 1.0 V
0.5 V
0 V
1.0 V
0.5 V
0 V
± DIAGNOSTICSENGINE
DI±79
2001 PRIUS (RM778U)
(c) Drive the vehicle at 89 km/h (55 mph) or more for 5 min. or more.
(d) After confirming that the waveforms of the oxygen sensor, bank 1 sensor 1 (OX1), oscillate around 0.5
V during feedback to the ECM, check the waveform of the oxygen sensor, bank 1 sensor 2 (OX2).
HINT:
If there is a malfunction in the system, the waveform of the
oxygen sensor, bank 1 sensor 2 (OX2),is shown on the
left.
There are some cases where, even though a malfunction
exists, the MIL may either light up or not light up.
Normal waveform of OX2 is a smooth line of 0.6 to 0.7 V.
INSPECTION PROCEDURE
HINT:
Read freeze frame data using TOYOTA hand±held tester or OBD II scan tool. Because freeze frame records
the engine conditions when the malfunction is detected, when troubleshooting it is useful for determining
whether the vehicle was running or stopped, the engine warmed up or not, the air±fuel ratio lean or rich, etc.
at the time of the malfunction.
1 Are there any other codes (besides DTC P0420) being output?
YES Go to relevant DTC chart.
NO
2 Check gas leakage on exhaust system.
NG Repair or replace.
OK
3 Check for open and short in harness and connector between heated oxygen
sensor (bank 1 sensor 1, 2) and ECM.
NG Repair or replace harness or connector.
OK