Toyota Tundra. Manual — part 1239

provide the ECM with feedback so that it can control the air-fuel ratio. The ECM determines the deviation from
the stoichiometric air-fuel ratio level, and regulates the fuel injection time. If the A/F sensor malfunctions, the
ECM is unable to control the air-fuel ratio accurately.

The A/F sensor is the planar type and is integrated with the heater, which heats the solid electrolyte (zirconia
element). This heater is controlled by the ECM. When the intake air volume is low (the exhaust gas temperature
is low), a current flows into the heater to heat the sensor, in order to facilitate accurate oxygen concentration
detection. In addition, the sensor and heater portions are the narrow type. The heat generated by the heater is
conducted to the solid electrolyte through the alumina, therefore the sensor activation is accelerated.

In order to obtain a high purification rate of the carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide
(NOx) components in the exhaust gas, a TWC is used. For the most efficient use of the TWC, the air-fuel ratio
must be precisely controlled so that it is always close to the stoichiometric level.

*: Value changes inside the ECM. Since the A/F sensor is the current output element, a current is converted into
a voltage inside the ECM. Any measurements taken at the A/F sensor or ECM connectors will show a constant
voltage.

Fig. 200: Air-Fuel Ratio Graph

DTC TROUBLE DETECTION CONDITION CHART

DTC

No.

DTC Detection Condition

Trouble Area



Open or short in A/F
sensor (bank 1, 2 sensor 1)
circuit



A/F sensor (bank 1, 2
sensor 1)

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (1GR-FE) - Tundra

HINT:



DTCs P2195 and P2196 indicate malfunctions related to bank 1 A/F sensor circuit.



DTCs P2197 and P2198 indicate malfunctions related to bank 2 A/F sensor circuit.



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



Bank 2 refers to the bank that includes No. 2 cylinder.



When any of these DTCs are set, check the A/F sensor voltage output by entering the following menus:
Powertrain/Engine and ECT/Data List/A/F Control System/AFS B1 S1 or AFS B2 S1.



Short-term fuel trim values can also be read using the Techstream.



The ECM regulates the voltages at the A1A+, A2A+, A1 A- and A2A- terminals of the ECM to a
constant level. Therefore, the A/F sensor voltage output cannot be confirmed without using the
Techstream.

P2195
P2197

Conditions (a) and (b) continue for 5 seconds or more (2 trip
detection logic)

a. Air-Fuel Ratio (A/F) sensor voltage more than 3.8 V

b. Heated Oxygen (HO2) sensor voltage rise from less than

0.21 V to 0.59 V or more



A/F sensor (bank 1, 2
sensor 1) heater



A/F sensor heater



Integration relay



Air induction system
circuits



Fuel pressure



Fuel injector



ECM

While fuel-cut operation performed (during vehicle
deceleration), air-fuel ratio (A/F) sensor current 3.6 mA or more
for 3 seconds (2 trip detection logic)



A/F sensor



ECM

P2196
P2198

Conditions (a) and (b) continue for 5 seconds or more (2 trip
detection logic)

a. A/F sensor voltage less than 2.8 V

b. HO2 sensor voltage falls from 0.59 V or more to less than

0.21V



Open or short in A/F
sensor (bank 1, 2 sensor 1)
circuit



A/F sensor (bank 1, 2
sensor 1)



A/F sensor (bank 1, 2
sensor 1) heater



A/F sensor heater circuits



Air induction system



Integration relay



Fuel pressure



Fuel injector



ECM

While fuel-cut operation performed (during vehicle
deceleration), air-fuel ratio (A/F) sensor current less than 1.4
mA for 3 seconds (2 trip detection logic)



A/F sensor



ECM

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (1GR-FE) - Tundra



If a A/F sensor malfunction is detected, the ECM sets a DTC.

MONITOR DESCRIPTION

Sensor voltage detection monitor

Under the air-fuel ratio feedback control, if the A/F sensor voltage output indicates rich or lean for a certain
period of time, the ECM determines that there is a malfunction in the A/F sensor. The ECM illuminates the MIL
and sets a DTC.

Example:

If the A/F sensor voltage output is less than 2.8 V (very rich condition) and HO2 sensor output voltage falls
from 0.59 V or more to less than 0.21 V for 5 seconds, the ECM sets DTC P2196 or P2198. Alternatively, if the
A/F sensor voltage output is more than 3.8 V (very lean condition) and HO2 sensor output voltage rises from
less than 0.21 V to 0.59 V or more for 5 seconds, DTC P2195 or P2197 is set.

Sensor current detection monitor

A rich air-fuel mixture causes a low A/F sensor current, and a lean air-fuel mixture causes a high A/F sensor
current. Therefore, the sensor output becomes low during acceleration, and it becomes high during deceleration
with the throttle valve fully closed. The ECM monitors the A/F sensor current during fuel-cut and detects any
abnormal current values.

If the A/F sensor output is 3.6 mA or more for more than 3 seconds of cumulative time, the ECM interprets this
as a malfunction in the A/F sensor and sets DTC P2195 or P2197 (high-side stuck). If the A/F sensor output is
less than 1.4 mA for more than 3 seconds of cumulative time, the ECM sets DTC P2196 or P2198 (low-side
stuck).

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (1GR-FE) - Tundra

Fig. 201: Air Fuel Ratio Sensor Current Graph

MONITOR STRATEGY

MONITOR STRATEGY

TYPICAL ENABLING CONDITIONS

ALL

TYPICAL ENABLING CONDITIONS

Related DTCs

P2195: A/F sensor (Bank 1) signal stuck lean
P2196: A/F sensor (Bank 1) signal stuck rich
P2197: A/F sensor (Bank 2) signal stuck lean
P2198: A/F sensor (Bank 2) signal stuck rich

Required Sensors/Components (Main)

A/F sensor

Required Sensors/Components (Related)

HO2 sensor

Frequency of Operation

Continuous

Duration

5 seconds: Sensor voltage detection monitor
3 seconds: Sensor current detection monitor

MIL Operation

2 driving cycles

Sequence of Operation

None

P0031, P0032, P0051, P0052 (A/F sensor heater -
Sensor 1)
P0037, P0038, P0057, P0058 (O2 Sensor heater -

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (1GR-FE) - Tundra