2001 TOYOTA PRIUS Service Repair Manual

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

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

DI±80
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)
4 Check oxygen sensor (bank 1 sensor 1) (See page DI±50).
NG Repair or replace.
OK
5 Check oxygen sensor (bank 1 sensor 2) (See page DI±59).
NG Repair or replace.
OK
Replace three±way catalytic converter.

A14039
ECM
VSV
for EVAP
Charcoal Canister
Fuel Tank Fig. 1
(3) (8)
(9)
(1) (7)
Vapor Pressure
Sensor VSV for
CCV(4)(5)
(6)(2)
Fresh
Air
ValveVSV for Purge Flow
switching Valve
± DIAGNOSTICSENGINE
DI±81
2001 PRIUS (RM778U)
DTC P0440 Evaporative Emission Control System
Malfunction
CIRCUIT DESCRIPTION
The vapor pressure sensor, VSV for canister closed valve (CCV) and VSV for purge flow switching valve are
used to detect abnormalities in the evaporative emission control system.
The ECM decides whether there is an abnormality in the evaporative emission control system based on the
vapor pressure sensor signal.
DTC P0440 is recorded by the ECM when evaporative emissions leak from the components or when the
vapor pressure sensor malfunctions.

DTC No.DTC Detecting ConditionTrouble Area
P0440When the vacuum applied to the sealed tank cannot be kept for
a fixed time.

Hose or tube cracked, hole, damaged or loose seal ((3) and
(4) in Fig. 1)

Fuel tank cap incorrectly installed

Fuel tank cap cracked or damaged

Vacuum hose cracked, holed, blocked, damaged or discon-
nected ((1) (2) and (3) in Fig. 1)

Fuel tank cracked, holed or damaged

Charcoal canister cracked, holed or damaged

Open or short in vapor pressure sensor circuit

Vapor pressure sensor

ECM
DI7ST±01

A14054
11 1A 6
1K
BR 3
1BG±R
1
2 CAIA2
32E9ECM
CCV EVP1
E2
PTNK
VC E7
LE925
2
15V2 VSV
(EVAP)4
TBP Engine Room J/B
B±R 1
1 11F
1 1EFI
Relay
3
2
112
6 B EFI
W±B
BC1
V5 VSV (Purge Flow
Switching Valve) B±G
IE A F12
MAIN
Battery1 5
7 B
BB
C B
4 3
5
2
13
1 1F13
F13
J1
J/CJ7
J/C
A AW±BMREL
29
E9
E8
E9
E818
22 G±R
J/C
J5 J4
IA1 BB19
J4J5 J5J/C
V4
Vapor Pressure
Sensor
Y±RJ8
J/C
Y±R
BC1 BC1 BC1
BC1 BC1BC1
IO1
2
2
2 V6 VSV (Canister Closed Valve)
B
C Y±R
Y±R L±R L±RBRL B±R B CA
AB
R±L
FL Block No. 1
F18
FL Block No. 2 DI±82
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)
WIRING DIAGRAM
INSPECTION PROCEDURE
HINT:

If DTC P0441, P0446, P0450 or P0451 is output after DTC P0440, first troubleshoot DTC P0441,
P0446, P0450 or P0451. If no malfunction is detected, troubleshoot DTC P0440 next.

Ask the customer whether, after the MIL came on, the customer found the fuel tank cap loose and tight-
ened it. Also ask the customer whether the fuel tank cap was loose when refuelling. If the fuel tank cap
was loose, it was the cause of the DTC. If the fuel tank cap was not loose or if the customer was not
sure if it was loose, troubleshoot according to the following procedure.

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 was warmed up or not, the air±fuel
ratio was lean or rich, etc. at the time of the malfunction.