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DI-512
DIAGNOSTICS - ENGINE (2UZ-FE)
DIDRB-01
DTC P0037 Oxygen Sensor Heater Control Circuit Low
(Bank 1 Sensor 2)
DTC P0038 Oxygen Sensor Heater Control Circuit High
(Bank 1 Sensor 2)
DTC P0057 Oxygen Sensor Heater Control Circuit Low
(Bank 2 Sensor 2)
DTC P0058 Oxygen Sensor Heater Control Circuit High
(Bank 2 Sensor 2)
DI-513
DIAGNOSTICS - ENGINE (2UZ-FE)
CIRCUIT DESCRIPTION
To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three-way cata-
lytic 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 heated oxygen sensor has the characteristic which its output voltage changes suddenly in the vicinity
of the stoichiometric air-fuel ratio. This characteristic is used to detect the oxygen concentration in the ex-
haust gas and provide the ECM with feedback to control the air-fuel ratio.
When the air-fuel ratio becomes LEAN, the oxygen concentration in the exhaust increases and the heated
oxygen sensor informs the ECM of the LEAN condition (low voltage, i.e. less than 0.45 V).
When the air-fuel ratio is RICHER than the stoichiometric air-fuel ratio, the oxygen concentration in the ex-
haust gas is reduced and the heated oxygen sensor informs the ECM of the RICH condition (high voltage,
i.e. more than 0.45 V). The ECM judges by the voltage output from the heated oxygen sensor whether the
air-fuel ratio is RICH or LEAN and controls the injection time accordingly. However, if malfunction of the
heated oxygen sensor causes output of abnormal voltage, this disables the ECM for performing an accurate
air-fuel ratio control. The heated 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 temperature of the exhaust gas is
low) current flows to the heater to heat the sensor for accurate oxygen concentration detection.
Atmospheric Air
Ideal Air-Fuel Mixture
Housing
Output Voltage
Solid Electrolyte
(Zirconia Element)
Platinum Electrode
Heater
Coating (Ceramic)
Cover Richer - Air Fuel Ratio - Leaner
Exhaust Gas
B17386
HINT:
The ECM provides a pulse width modulated control circuit to adjust current through the heater. The heated
oxygen sensor heater circuit uses a relay on the B+ side of the circuit.
Reference (Bank 1 Sensor 1 System Drawing):
Heated Oxygen Sensor ECM
EFI Relay
From Heater HT1B
Battery
EFI Fuse No. 1 EFI Fuse No. 2
Sensor OX1B
Duty
Control
E2
Ground
MREL
A21040
DI-514
DIAGNOSTICS - ENGINE (2UZ-FE)
DTC No. DTC Detecting Condition Trouble Area
S Open in heater circuit of heated oxygen sensor
P0037 Heater current is 0.25 A or less when the heater o erates with
operates S Heated oxygen sensor heater
P0057 more than 10.5 V positive battery voltage S EFI relay
S ECM
S Short in heater circuit of heated oxygen sensor
P0038 S Heated oxygen sensor heater
When heater operates, heater current exceeds 2.0 A
P0058 S EFI relay
S ECM
HINT:
S Bank 1 refers to bank that includes cylinder No. 1.
S Bank 2 refers to bank that does not includes cylinder No. 1.
S Sensor 1 refers to the sensor closer to the engine assembly.
S Sensor 2 refers to the sensor farther away from the engine assembly.
MONITOR DESCRIPTION
The sensing portion of the heated oxygen sensor has a zirconia element which is used to detect oxygen
concentration in the exhaust. If the zirconia element is at the proper temperature and difference of the oxy-
gen concentration between the inside and outside surface of sensor is large, the zirconia element will gener-
ate voltage signals. In order to increase the oxygen concentration detecting capacity in the zirconia element,
the ECM supplements the heat from the exhaust with heat from a heating element inside the sensor. When
current in the sensor is out of the standard operating range, the ECM interprets this as a fault in the heated
oxygen sensor and sets a DTC.
Example:
The ECM will set a high current DTC if the current in the sensor is more than 2.0 A when the heater is OFF.
Similarly, the ECM will set a low current DTC if the current is less than 0.3 A when the heater is ON.
MONITOR STRATEGY
Rear HO2S heater (Bank 1) range check (Low
P0037
Current)
Rear HO2S heater (Bank 1) range check (High
P0038
Current)
Related DTC
R l t d DTCs
Rear HO2S heater (Bank 2) range check (Low
P0057
Current)
Rear HO2S heater (Bank 2) range check (High
P0058
Current)
Main sensors/components HO2S heater
Required sensors/components
R i d / t
Related sensors/components Vehicle speed sensor (VSS)
Frequency of operation Continuous
P0037, P0057: 0.5 seconds
Duration
P0038, P0058: 0.3 seconds
MIL operation Immediate
Sequence of operation None
DI-515
DIAGNOSTICS - ENGINE (2UZ-FE)
TYPICAL ENABLING CONDITIONS
Specification
Item
It
Minimum Maximum
The monitor will run whenever this DTC is
See page DI-437
not present
All:
Battery voltage 10.5 V -
Engine Running
Starter OFF
Catalyst intrusive monitoring Not operating
Intrusive heating Not operating
P0037, P0057 (Low current):
When the following conditions are met: 0.5 sec. -
1. All of the following conditions are met: Condition (a), (b), (c), (d) and (e)
(a) Learned heater current during heater
Completed
OFF
(b) Intrusive heating Not operating
(c) Heating is OFF - 0.1 sec.
(d) Heater current - 0.3 A
(e) Intrusive heating for high current moni-
Not operating
tor
2. Following condition is met: -
Time after heaters are OFF 1 sec. -
P0038, P0058 (High current):
When the following conditions are met: 0.3 sec. -
1. All of the following conditions are met: Condition (a), (b), (c) and (d)
(a) Learned heater current during heater
Completed
OFF
(b) Intrusive heating Not operating
(c) Heating is OFF - 0.1 sec.
(d) Heater current 2A -
2. Following condition is met: -
Time after heaters are OFF 1 sec. -
DI-516
DIAGNOSTICS - ENGINE (2UZ-FE)
TYPICAL MALFUNCTION THRESHOLDS
Detection Criteria Threshold
P0037, P0057 (Low current):
Heater ON
Heater current Less than 0.3 A
Intrusive heating Operating
P0038, P0058 (High current):
Either of the following conditions is met: Condition 1 or 2
1. All of the following conditions (a) and (b) are met: With intrusive heating
(a) Heater ON
(b) Heater current 2 A or more
2. All of the following conditions (c), (d) and (e) are met: Without intrusive heating
(c) Intrusive heating of learned heater current Operating
(d) Learned heater current during heater OFF Operating
(e) Heater current More than 2 A
COMPONENT OPERATING RANGE
Parameter Standard Value
HO2S heater current 0.4 to 1 A (at idle, warmed-up engine and +B: 11 to 14 V)
MONITOR RESULT
Refer to page DI-445 for detailed information.
The test value and test limit information are described as shown in the following table. Check the monitor
result and test values after performing the monitor drive pattern (see page DI-446).
S TID (Test Identification Data) is assigned to each emissions-related component.
S TLT (Test Limit Type):
If TLT is 0, the component is malfunctioning when the test value is higher than the test limit.
If TLT is 1, the component is malfunctioning when the test value is lower than the test limit.
S CID (Component Identification Data) is assigned to each test value.
S Unit Conversion is used to calculate the test value indicated on generic OBD ll scan tools.
TID $04: HO2S heater
TLT CID Unit Conversion Description of Test Data Description of Test Limit
Multiply by 0.000076 Maximum HO2S heater current
1 $02 Malfunction threshold for HO2S heater
(A) (Bank 1 Sensor 2)
Multiply by 0.000076 Maximum HO2S heater current
1 $20 Malfunction threshold for HO2S heater
(A) (Bank 2 Sensor 2)
DI-517
DIAGNOSTICS - ENGINE (2UZ-FE)
WIRING DIAGRAM
Access Cab, Standard Cab:
Engine Room R/B ECU
EFI Relay J/C
9 26 8
W-B 2 GR-G J26 J27 GR-G E3 MREL
2
2 1
B-R 2 2 H6
5 3 W-L Heated Oxygen Sensor
(Bank 2 Sensor 2)
Engine Room R/B J1 R 2 +B HT 1 5
Y-B E6 HT2B
EFI No. 2 J/C
(Shielded) 33
B B B-W
2 2 OX 3 E6 OX2B
2 1
W-L 4 E W
R J8 H4
J/C J/C Heated Oxygen
7 24 22
R R R Sensor
J26 J27 IE1
A A (Bank1 Sensor2)
1
R 2 +B HT 1 R-L E7 HT1B
2
(Shielded) 18
B-W
E OX 3 E7 OX1B
2 4 B
Engine
EFI Room
No. 1 R/B
28
1 B-W E7 E2
E E
2 J64
J/C 1
A E BR
E5 E1
J18
J/C B-L (*1)
BR
A B (*2)
W-B
EA Battery EW EC
*1: Towing Package
*2: Except Towing Package
A23605
DI-518
DIAGNOSTICS - ENGINE (2UZ-FE)
Double Cab:
ECU
11 8
B-W B-W
IA10 E3 MREL
R
6 2H 2 2A
22 IE1
C J48 H4
EFI Heated Oxygen Sensor
J/C R (Bank1 Sensor2)
Engine Room R/B
No. 2 1
A J47 R R-L E7 HT1B
2 3 +B HT
2 1 (Shielded)
EFI 18
R R B-W E7 OX1B
Relay E OX
4 3 B
1 5 H6
2 IA4 R Heated Oxygen
EFI Sensor
No. 1 (Bank2 Sensor2)
5
+B HT Y-B E6 HT2B
1 2F 1 2D 2 1
(Shielded) 33
B-W OX E6 OX2B
4 E 3 W
W-B B E E
J64
J/C
28
B-W E
A 10 E7 E2
F13
J34 FL 1
J/C BR
Block E5 E1
A 12
B BR
W-B
EA Battery EY EC
A23606
DI-519
DIAGNOSTICS - ENGINE (2UZ-FE)
INSPECTION PROCEDURE
HINT:
Read freeze frame data using hand-held tester. Because freeze frame records the engine conditions when
the malfunction is detected. When troubleshooting, it is useful to determine whether the vehicle was running
or stopped, the engine was warmed up or not, the air-fuel ratio was lean or rich, etc. when a malfunction
occurred.
1 Check resistance of heated oxygen sensor heater.
Components Side: PREPARATION:
+B HT Disconnect the H4 or H6 heated oxygen sensor connector.
CHECK:
Measure resistance between terminals of the heated oxygen
H4
sensor.
H6 OK:
Standard:
E1 OX Tester Connection Specified Condition
Bank 1 Sensor 2, Bank 2 Sensor 2 A21341
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