2001 TOYOTA PRIUS heater

± DIAGNOSTICSENGINE
DI±15
2001 PRIUS (RM778U)P0133
(DI±54)
Oxygen Sensor Circuit Slow Re-
sponse (Bank 1 Sensor 1)
Open or short in heated oxygen sensor circuit
Heated oxygen sensor
Air induction system
EGR system
Fuel pressure
Injector
ECM

P0135
(DI±57)Oxygen Sensor Heater Circuit
Malfunction (Bank 1 Sensor 1)Open or short in heater circuit of heated oxygen sensor
Heated oxygen sensor heater
ECM

P0136
(DI±59)Oxygen Sensor Circuit Malfunc-
tion (Bank 1 Sensor 2)Open or short in heated oxygen sensor circuit
Heated oxygen sensor
P0141
(DI±57)Oxygen Sensor Heater Circuit
Malfunction (Bank 1 Sensor 2)Same as DTC No. P0135
P0171
(DI±61)System too Lean (Fuel Trim)
Air induction system
Injector blockage
Mass air flow meter
Engine coolant temp. sensor
Fuel pressure
Gas leakage on exhaust system
Open or short in heated oxygen sensor (bank 1 sensor 1)
circuit
Heated oxygen sensor (bank 1 sensor 1)

P0172
(DI±61)System too Rich (Fuel Trim)
Injector leak, blockage
Mass air flow meter
Engine coolant temp. sensor
Ignition system
Fuel pressure
Gas leakage on exhaust system
Open or short in heated oxygen sensor (bank 1, 2 sensor 1)
circuit
Heated oxygen sensor (bank 1, 2 sensor 1)
ECM

P0300
(DI±65)Random/Multiple Cylinder Misfire
DetectedOpen or short in engine wire
Connector connection
Vac m hose connectionP0301
(DI±65)Cylinder 1 Misfire Detected
Vacuum hose connection
Ignition system
Injector
P0302
(DI±65)Cylinder 2 Misfire Detected
j
Fuel pressure
EGR system

Manifold absolutepressure sensor

P0303
(DI±65)Cylinder 3 Misfire Detected
Manifold absolute pressure sensor
Engine coolant temp. sensor
Compression pressure
Vl lP0304
(DI±65)Cylinder 4 Misfire Detected
Valve clearance
Valve timing
ECM
P0325
(DI±71)Knock Sensor 1 Circuit Malfunc-
tion (Bank 1)Open or short in knock sensor 1 circuit
Knock sensor 1 (looseness)
ECM

P0335
(DI±74)Crankshaft Position Sensor ºAº
Circuit Malfunction
Open or short in crankshaft position sensor circuit
Crankshaft position sensor
Signal plate (Timing belt guide)
Crankshaft timing pulley
ECM


P21242 FI7210
A04485
Atmosphere
Flange
Platinum Electrode
Solid Electrolyte
(Zirconia Element)
Platinum Electrode
Heater
Coating (Ceramic)
Exhaust Gas CoverIdeal Air±Fuel Mixture
Output Voltage
Richer ± Air Fuel Ratio ± Leaner
DI±44
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)
DTC P0125 Insufficient Temp. for Closed Loop
Fuel Control
CIRCUIT DESCRIPTION
To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three±way
catalytic converter is used, but for the most efficient use of the three±way catalytic converter, the air±fuel
ratio must be precisely controlled so that it is always close to the stoichiometric air±fuel ratio.
The oxygen sensor has the characteristic whereby its output voltage changes suddenly in the vicinity of the
stoichiometric air±fuel ratio. This is used to detect the oxygen concentration in the exhaust gas and provide
feedback to the computer for control of the air±fuel ratio.
When the air±fuel ratio becomes LEAN, the oxygen concentration in the exhaust increases and the oxygen
sensor informs the ECM of the LEAN condition (small electromotive force: < 0.45 V).
When the air±fuel ratio is RICHER than the stoichiometric air±fuel ratio the oxygen concentration in the ex-
haust gas in reduced and the oxygen sensor informs the ECM of the RICH condition (large electromotive
force: > 0.45V).
The ECM judges by the electromotive force from the oxygen sensor whether the air±fuel ratio is RICH or
LEAN and controls the injection time accordingly. However, if malfunction of the oxygen sensor causes out-
put of abnormal electromotive force, the ECM is unable to perform accurate air±fuel ratio control.
The oxygen sensors include a heater which heats the zirconia element. The heater is controlled by the ECM.
When the intake air volume is low (the temp. of the exhaust gas is low) current flows to the heater to heat
the sensor for accurate oxygen concentration detection.
DTC No.DTC Detecting ConditionTrouble Area
P0125
After the engine is warmed up, oxygen sensor (bank 1 sensor
1) output does not indicate RICH (
0.45 V) even once when
conditions (a), (b), and (c) continue for at least 50 sec.
(a) Engine speed: 800 rpm or more
(b) Vehicle speed: 40 ± 100 km/h (25 ± 62 mph)
(c) 20 sec. or more after starting engine

Fuel system

Air induction system

Injector

Ignition system

Gas leakage on exhaust system

Open or short in heated oxygen sensor (bank 1 sensor 1)
circuit

Heated oxygen sensor (bank 1 sensor 1)

ECM
DI6V2±03

± DIAGNOSTICSENGINE
DI±57
2001 PRIUS (RM778U)
DTC P0135 Heated Oxygen Sensor Heater Circuit
Malfunction (Bank1 Sensor1)
DTC P0141 Heated Oxygen Sensor Heated Circuit
Malfunction (Bank1 Sensor2)
CIRCUIT DESCRIPTION
Refer to DTC P0125 on page DI±44.
DTC No.DTC Detecting ConditionTrouble Area
P0135
When the heater operates, heater current exceeds 2 A
(2 trip detection logic)
Open or short in heater circuit of heated oxygen sensor
Htd htP0135
P0141Heater current of 0.2 A or less when the heater operates
(2 trip detection logic)
Heated oxygen sensor heater

ECM
HINT:

Bank 1 refers to the bank that includes cylinder No.1.

Sensor 1 refers to the sensor closer to the engine body.

Sensor 2 refers to the sensor farther away from the engine body.
WIRING DIAGRAM
Refer to DTC P0125 on page DI±44.
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.
DI6V5±02

A13626
ON
HT1A
(+) (±) HT1B
DI±58
± DIAGNOSTICSENGINE
2001 PRIUS (RM778U)
1 Check voltage between terminals HT1A, HT1B of ECM connectors and body
ground.
PREPARATION:
(a) Remove the ECM with connector still connected (See
page SF±62).
(b) Turn the ignition switch ON.
CHECK:
Measure voltage between terminals HT1A, HT1B of ECM con-
nectors and body ground.
HINT:

Connect terminal HT1A to bank 1 sensor 1.

Connect terminal HT1B to bank 1 sensor 2.
OK:
Voltage: 9 ± 14 V
OK Check and replace ECM (See page IN±41).
NG
2 Check resistance of heated oxygen sensor heater (See page SF±58).
NG Replace heated oxygen sensor.
OK
Check and repair harness or connector between EFI relay (Marking: EFI), heated oxygen sensor
and ECM (See page IN±41).

AB0119H01298H01299
Airbag Sensor Assembly
ON
IG1
ACC
(+) (±)
H01249
ON
DI±636
± DIAGNOSTICSSUPPLEMENTAL RESTRAINT SYSTEM
2001 PRIUS (RM778U)
2 Check source voltage.
PREPARATION:
Connect negative (±) terminal cable to the battery.
CHECK:
(a) Turn ignition switch ON.
(b) Measure the voltage between body ground and each of
IG1 and IG2 on the sensor and operate electric system
(defogger, wiper, headlight, heater blower, etc.).
OK:
Voltage: 10 ± 14 V
NG Check harness between battery and airbag sen-
sor assembly, and check battery and charging
system.
OK
3 Does SRS warning light turn off?
PREPARATION:
(a) Turn the ignition switch to LOCK.
(b) Connect the steering wheel pad connector.
(c) Connect the front passenger airbag assembly connector.
(d) Connect the side airbag assembly connectors.
(e) Connect the seat belt pretensioner connectors.
(f) Connect the airbag sensor assembly connectors.
(g) Connect the front airbag sensor connectors.
(h) Connect the side airbag sensor assembly connectors.
(i) Turn the ignition switch to ON.
CHECK:
Operate electric system (defogger, wiper, headlight, heater
blower, etc.) and check that SRS warning light goes off.
NO Check for DTCs. If a DTC is output, perform trou-
bleshooting for the DTC. If a normal code is out-
put, replace airbag sensor assembly.
YES
From the results of the above inspection, the malfunctioning part can now be considered normal.
To make sure of this, use the simulation method to check.

DI7S3±01
± DIAGNOSTICSAIR CONDITIONING SYSTEM
DI±879
2001 PRIUS (RM778U)
PROBLEM SYMPTOMS TABLE
SymptomSuspect AreaSee page
Whole function of the does not operate3. A/C amplifier
4. IG power source circuitIN±41
DI±916
Air Flow Control: No blower operation1. IG power source circuit
2. Heater main relay circuit
3. Blower motor circuit
4. A/C amplifierDI±916
DI±921
DI±924
IN±41
Air Flow Control: No blower control1. Heater main relay circuit
2. Blower motor circuit
3. A/C amplifierDI±921
DI±924
IN±41
Air Flow Control: Insufficient air flow1. Blower motor circuitDI±924
Temperature Control: No cool air comes out1. Refrigerant volume
2. Drive belt tension
3. Refrigeration system inspection with manifold gauge set
4. Compressor circuit
5. Pressure switch circuit
6. Compressor lock sensor circuit
7. Air mix damper position sensor circuit
8. Air mix damper control servomotor circuit
9. Room temperature sensor circuit
10.Ambient temperature sensor circuit
11. A/C amplifierAC±3
AC±15
AC±3
DI±927
DI±894
DI±891
DI±897
DI±906
DI±874
DI±879
IN±41
Temperature Control: No warm air comes out1. Air mix damper position sensor circuit
2. Air mix damper control servomotor circuit
3. DC/DC converter circuit
4. PTC heater circuit
5. Room temperature sensor circuit
6. Ambient temperature sensor circuit
7. Evaporator temperature sensor circuit
8. A/C amplifierDI±897
DI±906
DI±934
DI±937,
DI±942
DI±876
DI±882
DI±885
IN±41
Temperature Control: Output air is warmer or cooler that the set
temperature or response is slow1. Refrigerant volume
2. Drive belt tension
3. Refrigeration system inspection with manifold gauge set
4. Radiator fan and condenser fan circuit
5. Solar sensor circuit
6. Room temperature sensor circuit
7. Ambient temperature sensor circuit
8. Evaporator temperature sensor circuit
9. Air mix damper position sensor circuit
10.Air mix damper control servomotor circuit
11. Evaporator
12.Heater radiator
13.Expansion valve
14.A/C amplifierAC±3
AC±15
AC±3
DI±947
DI±888
DI±876
DI±879
DI±885
DI±897
DI±906
AC±28
AC±28
AC±52
IN±41
Temperature Control: No temperature control (only Max. cool or
Max. warm)1. Room temperature sensor circuit
2. Ambient temperature sensor circuit
3. Air mix damper position sensor circuit
4. Air mix damper control servomotor circuit
5. A/C amplifierDI±876
DI±882
DI±897
DI±906
IN±41
No air inlet control1. Air inlet damper position sensor circuit
2. Air inlet damper control servomotor circuit
3. A/C amplifierDI±900
DI±909
IN±41

I18388
A/C Amplifier
11
A7MPX+ GR
4
MPX+
BJ6
J/C
HTR Relay
J/C
Battery4
A7
MP2+ C11
Combination Meter
MPX±
11 GR±B
MPX1 MPX2
10
B8
14 13
11
B8 MPX+
MPX±
MPD2
MPD1
Instrument Panel J/B
HRLY6
2FL±O
BR R 4
1F
5 3
2
HTR
13
1J
8
1K
3
1B
3
1K
To Blower Motor
W13
IE1
R
A
J23
CJ22
R
FL Block
No. 1 DC/DC
B±G
F11 1
F13 1
1
MAINW±B
A F18
FL Block
No. 2
AWInstrument Panel J/B
1
2H
8
2K
IG1
Relay
3
25
1AM1
W±GI15
Ignition
SW
HTRAM1
3
2B
6
2D
3
2D
IG12
4
B±Y
J11
J/C
ID
IE W±BA
AJ1
J/C
3 2
E10 E10ECM
GR
GR±LC1
Gateway ECU
GR±B
J7 J/C
Engine Room J/B Body ECU DI±926
± DIAGNOSTICSAIR CONDITIONING SYSTEM
2001 PRIUS (RM778U)
Heater Main Relay Circuit
CIRCUIT DESCRIPTION
The heater main relay is switched on by signals from the A/C amplifier. It supplies power to the blower motor.
WIRING DIAGRAM
DI7SK±01

BE1850 BE1844I00312125
3
125
3
4
4
I18394
Engine Room J/B
HTR
Fuse
± DIAGNOSTICSAIR CONDITIONING SYSTEM
DI±927
2001 PRIUS (RM778U)
INSPECTION PROCEDURE
1 Check heater main relay.
PREPARATION:
Remove heater main relay from engine room J/B.
CHECK:
Check continuity between each pair of terminals of heater main
relay shown below.
OK:
Tester connectionSpecified condition
1 ± 4No continuity
2 ± 4Continuity
3 ± 562.5 ± 90.9 W
PREPARATION:
Apply battery positive voltage between terminals 3 and 5.
CHECK:
Check continuity between each pair of terminal shown below.
OK:
Tester connectionSpecified condition
1 ± 2Continuity
2 ± 4No continuity
NG Replace hater main relay.
OK
2 Check HTR fuse
PREPARATION:
Remove HTR fuse from engine room J/B.
CHECK:
Check continuity of HTR fuse.
OK:
Continuity exists.
NG Check for short in all the harness and compo-
nents connected to the HTR fuse (See page
IN±41).
OK