P2255
DTC P2255 OXYGEN SENSOR REFERENCE GROUND CIRCUIT LOW (FOR A/F SENSOR) (BANK 2 SENSOR 1)HINT: These DTCs are recorded when A/F sensor has a malfunction, although the caption is oxygen sensor.
CIRCUIT DESCRIPTION
DTC Detecting Condition:
The A/F sensors is the planar type. Compared to the conventional type, the sensor and heater portions are narrower overall. Because the heat of the heater is conducted through the alumina to zirconia (of the sensor portion) it accelerates the activation of the sensor.
To obtain a high purification rate of the CO, HC and NOx components of the exhaust gas, a three-way catalytic converter is used. 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 A/F sensor has the characteristic that it provides output voltage* being approximately proportional to the existing air-fuel ratio.
The A/F sensor output voltage* is used to provide feedback for the ECM to control the air-fuel ratio.
By the A/F sensor output, the ECM can determine the deviation amount from the stoichiometric air-fuel ratio and control the proper injection time immediately. If the A/F sensor is out of order, ECM is unable to perform the accurate air-fuel ratio control.
The A/F sensor is equipped with 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), the current flows to the heater to heat the sensor for the accurate oxygen concentration detection.
*: The voltage value changes at the inside of the ECM only.
HINT:
- DTC P2237, P2238, P2239, P2251, P2252 and P2253 means malfunction related to the bank 1 A/F sensor circuit.
- DTC P2240, P2241, P2242, P2254, P2255 and P2256 means malfunction related to the bank 2 A/F sensor circuit.
- Bank 1 refers to the bank that includes cylinder No.1.
- Bank 2 refers to the bank that includes cylinder No.2.
MONITOR DESCRIPTION
Monitor Strategy:
Typical Enabling Conditions:
Typical Malfunction Thresholds:
The Air-Fuel Ratio (A/F) sensor varies its voltage output in proportion to the air-fuel ratio. If impedance (alternating current resistance) or voltage output of the sensor deviates greatly from the standard, the ECM determines that an open or short is in the A/F sensor circuit.
Wiring Diagram:
Step 1 - 2:
Step 3:
INSPECTION PROCEDURE
HINT:
Hand-held tester only:
Narrowing down the trouble area is possible by performing ACTIVE TEST of the following "A/F CONTROL" (A/F sensor, heated oxygen sensor or other trouble areas can be distinguished).
a. Perform ACTIVE TEST by the hand-held tester (A/F CONTROL).
HINT: "A/F CONTROL" is ACTIVE TEST which changes the injection volume to -12.5% or +25%.
1. Connect the hand-held tester to the DLC3 on the vehicle.
2. Turn the ignition switch ON.
3. Warm up the engine with the engine speed at 2,500 rpm for approx. 90 sec.
4. Select the item "DIAGNOSIS/ENHANCED OBD II/ACTIVE TEST/ A/F CONTROL".
5. Perform "A/F CONTROL" when idle condition (press the right or left button).
Result:
A/F sensor reacts in accordance with increase and decrease of injection volume:
+25% -> rich output: Less than 3.0 V
-12.5% -> lean output: More than 3.35 V
Heated oxygen sensor reacts in accordance with increase and decrease of injection volume:
+25% -> rich output: More than 0.55 V
-12.5% -> lean output: Less than 0.4 V
NOTE: There is a few second delay in the A/F sensor output and there is about 20 seconds delay in the heated oxygen sensor output.
The following procedure of A/F CONTROL enable the user to check its output (show its graph indication) of A/F sensor and heated oxygen sensor.
For displaying the graph indication, enter "ACTIVE TEST/ A/F CONTROL/USER DATA", then select "AFS B1S1 and O2S B1S2" or "AFS B2S1 and O2S B2S2" by pressing "YES" button and push "ENTER" button before pressing "F4" button.
HINT:
- If DTC P2237, P2238, P2239, P2251, P2252 or P2253 is displayed, check the bank 1 sensor 1 circuit.
- If DTC P2240, P2241, P2242, P2254, P2255 or P2256 is displayed, check the bank 2 sensor 1 circuit.
- Read freeze frame data using the hand-held tester or the OBD II scan tool, as freeze frame data records the engine conditions when a 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.