P2256
2UZ-FE ENGINE CONTROL SYSTEM: SFI SYSTEM: P2237: Oxygen (A/F) Sensor Pumping Current Circuit / Open (Bank 1 Sensor 1)
DTC P2237 - Oxygen (A/F) Sensor Pumping Current Circuit / Open (Bank 1 Sensor 1)
DTC P2238 - Oxygen (A/F) Sensor Pumping Current Circuit Low (Bank 1 Sensor 1)
DTC P2239 - Oxygen (A/F) Sensor Pumping Current Circuit High (Bank 1 Sensor 1)
DTC P2240 - Oxygen (A/F) Sensor Pumping Current Circuit / Open (Bank 2 Sensor 1)
DTC P2241 - Oxygen (A/F) Sensor Pumping Current Circuit Low (Bank 2 Sensor 1)
DTC P2242 - Oxygen (A/F) Sensor Pumping Current Circuit High (Bank 2 Sensor 1)
DTC P2252 - Oxygen (A/F) Sensor Reference Ground Circuit Low (Bank 1 Sensor 1)
DTC P2253 - Oxygen (A/F) Sensor Reference Ground Circuit High (Bank 1 Sensor 1)
DTC P2255 - Oxygen (A/F) Sensor Reference Ground Circuit Low (Bank 2 Sensor 1)
DTC P2256 - Oxygen (A/F) Sensor Reference Ground Circuit High (Bank 2 Sensor 1)
CAUTION / NOTICE / HINT
DESCRIPTION
The A/F sensor generates a voltage* that corresponds to the actual air-fuel ratio. This sensor voltage is used to 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 air-fuel ratio 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.
HINT:
- When either of these DTCs is set, check the A/F sensor output voltage by entering the following menus: Powertrain / Engine and ECT / Data List / A/F Control System / AFS Voltage B1 S1 or AFS Voltage B2 S1.
- Short-term fuel trim values can also be read using the Techstream.
- The ECM regulates the voltages at the A1A+ and A1A- or A2A+ and A2A- terminals of the ECM to a constant level. Therefore, the A/F sensor output voltage cannot be confirmed without using the Techstream.
HINT:
- DTCs P2237, P2238, P2239, P2252 and P2253 indicate malfunctions related to the bank 1 A/F sensor circuit.
- DTCs P2240, P2241, P2242, P2255 and P2256 indicate malfunctions related to the 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.
MONITOR DESCRIPTION
These DTCs are output when there is an open or short in the A/F sensor circuit, or if A/F sensor output drops.
To detect these problems, the voltage of the A/F sensor is monitored when turning the ignition switch to the ON position, and the admittance (admittance is an electrical term that indicates the ease of flow of current) is checked while driving. If the voltage of the A/F sensor is between 0.6 V and 4.5 V, it is considered normal. If the voltage is outside of the specified range, or the admittance is less than the standard value, the ECM will determine that there is a malfunction in the A/F sensor. If the same malfunction is detected in the next driving cycle, the MIL is illuminated and a DTC is set.
The Air-Fuel Ratio (A/F) sensor varies its output voltage in proportion to the air-fuel ratio. If the A/F sensor impedance (alternating current resistance) or output voltage deviates greatly from the standard range, the ECM determines that there is an open or short in the A/F sensor circuit.
MONITOR STRATEGY
TYPICAL ENABLING CONDITIONS
P2237, P2238, P2240, P2241:
P2239, P2242, P2252, P2253, P2255, P2256:
A/F sensor - open circuit between AF+ and AF-
A/F sensor - Low impedance
Other:
TYPICAL MALFUNCTION THRESHOLDS
P2237 and P2240:
P2238 and P2241:
P2239 and P2242:
P2252 and P2255:
P2253 and P2256:
WIRING DIAGRAM
INSPECTION PROCEDURE
HINT: Malfunctioning areas can be identified by performing the Control the Injection Volume for A/F sensor function provided in the Active Test. The Control the Injection Volume for A/F sensor function can help to determine whether the Air-Fuel Ratio (A/F) sensor, Heated Oxygen (HO2) sensor and other potential trouble areas are malfunctioning.
The following instructions describe how to conduct the Control the Injection Volume for A/ F sensor operation using the Techstream.
- (a) Connect the Techstream to the DLC3.
- (b) Start the engine and turn the Techstream ON.
- (c) Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
- (d) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/ F sensor.
- (e) Perform the Active Test operation with the engine idling (press the RIGHT or LEFT button to change the fuel injection volume).
- (f) Monitor the output voltages of the A/F and HO2 sensors (AFS Voltage B1 S1 and O2S B1 S2 or AFS Voltage B2 S1 and O2S B2 S2) displayed on the Techstream.
HINT:
- The Control the Injection Volume for A/F sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 25%.
- Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
Standard:
NOTE: The A/F sensor has an output delay of a few seconds and the HO2 sensor has a maximum output delay of approximately 20 seconds.
- Following the Control the Injection Volume for A/ F Sensor procedure enables technicians to check and graph the output voltages of both the A/F and HO2 sensors.
- Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/ F Sensor / A/F Control System / AFS Voltage B1 S1 and O2S B1 S2 or AFS Voltage B2 S1 and O2S B2 S2.
HINT: Read freeze frame data using the Techstream. Freeze frame data records the engine condition when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, if the engine was warmed up or not, if the air-fuel ratio was lean or rich, and other data from the time the malfunction occurred.
PROCEDURE
1. CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM) P2195
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- Continue to next step.
2. REPLACE AIR FUEL RATIO SENSOR
(a) Replace the air fuel ratio sensor Removal.
NEXT -- Continue to next step.
3. CHECK WHETHER DTC OUTPUT RECURS
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch to ON and turn the Techstream ON.
(c) Clear DTCs DTC Check / Clear.
(d) Start the engine.
(e) Allow the engine to idle for 5 minutes or more.
(f) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes / Pending.
(g) Read pending DTCs.
Result
B -- REPLACE ECM
A -- END