P2A00
DTC P2A00 O2 SENSOR NOT READY (BANK 1 / SENSOR 1)Component Location:
GENERAL DESCRIPTION
In order to control emissions of the CO, HC and NOx components of the exhaust gas, heated oxygen sensor (HO2S), mounted on the front side and rear side of catalytic converter, detects the oxygen content in the exhaust gas. The front HO2S signal is used to control air/fuel ratio (closed loop fuel control) and the rear HO2S signal is used to monitor front HO2S and catalyst for proper operation.The HO2S requires a minimum temperature to operate properly and provide a closed loop fuel control system. The HO2S contains the heater element to reduce its warming-up time and ensure its performance during all driving conditions.
The oxygen sensor generates a voltage that indicates the difference between the oxygen content of the exhaust stream and the oxygen content of ambient air. When the exhaust stream is "rich," there is more oxygen in the ambient air than in the exhaust stream, so the voltage will be higher.
Some oxygen sensor varieties use a "bias" voltage to achieve better resolution of the exhaust stream signal. Some oxygen sensor varieties use a pumping circuit to force ambient air into the sensor to maintain a more pure environment for comparison. In either case, a cold sensor will tend to indicate voltage values near the open circuit value. For the pumping current sensors, this open circuit value can be near 3.5 V. Since the Fuel control logic would incorrectly consider this reading to indicate a very rich mixture for an extended time, the fuel control logic can not use the oxygen sensor reading under such conditions.
The PCM controls this heater element by duty cycle. The main relay supplies voltage to the heater and the PCM provides a ground circuit for activating the heater.
DTC DESCRIPTION
Detect when the oxygen sensor reading has forced closed loop fuel control to stop executing, and Open Loop fuel control is in effect. This action will happen for OSP (flat plate) oxygen sensors that are not yet warmed up when the pumping current is in use. The California Air Resources Board (CARB) will not approve the current strategy without this modification. CARB considers this Open Loop operation to be a default mode of operation, and thus CARB expects the Malfunction Indicator Lamp (MIL) to be illuminated.
Checking output signals from B1S1 every 12 sec. under detecting condition, if an output signal is near 3.5 V for more than 10 sec., PCM sets P2A00. MIL (Malfunction Indication Lamp) turns on when the malfunction lasts till 1 driving cycle.
DTC Detecting Condition:
Specification:
Schematic Diagram:
Signal Waveform And Data:
SIGNAL WAVEFORM AND DATA
After warming-up, Releasing accelerator pedal suddenly around 4000rpm the HO2S signal reading will be lower than 200mV resulting from Fuel cut-off. Conversely, sudden depressing accelerator pedal HO2S signal reading will be around 0.6 V - 1.0 V. At idle, HO2S signal will be switching between lean (below 0.48 V) to rich (a above 0.48 V) normally.
MONITOR SCANTOOL DATA
1. Connect Scantool & Engine "ON"
2. Warm up the engine to normal operating temperature.
3. Monitor HO2S voltage (B1/S1) parameter on Scantool
Specification : Voltage will vary from 0.1 to 0.9 V
4. Is the HO2S parameter displayed within specifications?
YES: Fault is intermittent caused by poor contact in the sensor's and/or PCM's connector or was repaired and PCM memory was not cleared. Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure
NO: Go to "Component Inspection" procedure
COMPONENT INSPECTION
1. Visual Inspection of HO2S
1. Visually/physically inspect following items:
- Inspect the front HO2S for Contaminated, deteriorated or aged Front HO2S
- If contamination is evident on the HO2S, replace contaminated sensor
2. Is the HO2S visually / physically O.K?
YES: Go to "Check Performance of HO2S" as below
NO: Substitute with a known - good HO2S and check for proper operation. If the problem is corrected, replace HO2S and go to "Verification of Vehicle Repair"
2. Check performance of HO2S
1. Connect Scantool & Engine "ON"
2. Warm-up the engine to normal engine temperature.
3. Monitor signal waveform of HO2S with Scantool
Specification : Voltage will vary from 0.1 to 0.9 V
4. Is the sensor signal switching properly?
YES: Substitute with a known - good PCM and check for proper operation. If the problem is corrected, replace PCM and go to "Verification of Vehicle Repair" procedure.
NO: Substitute with a known - good HO2S and check for proper operation. If the problem is corrected, replace HO2S and go to "Verification of Vehicle Repair" procedure.
NOTE: There is a memory reset function on scantool that can erase optional parts automatically detected and memorized by PCM. Before or after testing PCM on the vehicle, use this function to reuse the PCM on the others
VERIFICATION OF VEHICLE REPAIR
After a repair, it is essential to verify that the fault has been corrected.
1. Monitor and record the Freeze Frame Data for the Diagnostic Trouble Code (DTC) which has been diagnosed.
2. Using a Scantool, Clear the DTCs
3. Operate the vehicle within conditions noted in the freeze frame data or enable conditions
4. Monitor that all readiness tests have been verified as "Complete"
5. Are any DTCs present?
YES: Go to the applicable trouble shooting procedure.
NO: System is performing to specification at this time.