P0051
2GR-FSE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0031: Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)
DTC P0031 - Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)
DTC P0032 - Oxygen (A/F) Sensor Heater Control Circuit High (Bank 1 Sensor 1)
DTC P0051 - Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 2 Sensor 1)
DTC P0052 - Oxygen (A/F) Sensor Heater Control Circuit High (Bank 2 Sensor 1)
DESCRIPTION
HINT:
- Although the DTC titles include oxygen sensor, these DTCs relate to the Air-Fuel Ratio (A/F) sensor.
- Sensor 1 refers to the sensor mounted in front of the Three-Way Catalytic Converter (TWC) and located near the engine assembly.
The A/F sensor generates 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 oxygen concentration detection. In addition, the sensor and heater portions are narrower than the conventional 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 to a voltage inside the ECM. Any measurements taken at the A/F sensor or ECM connectors will show a constant voltage.
HINT:
- DTCs P2195 and P2196 indicate malfunctions related to the bank 1 A/F sensor circuit.
- DTCs P2197 and P2198 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.
- When any of these DTCs are set, check the A/F sensor output voltage by selecting the following menu items on the Techstream: Powertrain / Engine and ECT / Data List / AFS B1 S1.
- Short-term fuel trim values can also be read using the Techstream.
- The ECM regulates the voltages at the A1A+, A2A+, A1A- and A2A- terminals of the ECM to a constant level. Therefore, the A/F sensor output voltage cannot be confirmed without using the Techstream.
- If a A/F sensor malfunction is detected, the ECM sets a DTC.
HINT:
- When any of these DTCs are set, the ECM enters fail-safe mode. The ECM turns off the A/F sensor heater in fail-safe mode. Fail-safe mode continues until the engine switch is turned off.
- The ECM provides a pulse width modulated control circuit to adjust the current through the heater. The A/F sensor heater circuit uses a relay on the +B side of the circuit.
HINT:
- Bank 1 refers to the bank that includes No. 1 cylinder.
- Bank 2 refers to the bank that does not include No. 1 cylinder.
- Sensor 1 refers to the sensor closest to the engine assembly.
- Sensor 2 refers to the sensor farthest away from the engine assembly.
MONITOR DESCRIPTION
1 The ECM uses information from the Air-Fuel Ratio (A/F) sensor to regulate the air fuel ratio and keep it close to the stoichiometric level. This maximizes the ability of the Three-Way Catalytic Converter (TWC) to purify the exhaust gases.
2 The A/F sensor detects oxygen levels in the exhaust gas and transmits the information to the ECM. The inner surface of the sensor element is exposed to the outside air. The outer surface of the sensor element is exposed to the exhaust gas. The sensor element is made of platinum coated zirconia and includes an integrated heating element.
3 The zirconia element generates a small voltage when there is a large difference in the oxygen concentrations between the exhaust gas and outside air. The platinum coating amplifies this voltage generation.
4 The A/F sensor is more efficient when heated. When the exhaust gas temperature is low, the sensor cannot generate useful voltage signals without supplementary heating. The ECM regulates the supplementary heating using a duty-cycle approach to adjust the average current in the sensor heater element. If the heater current is outside the normal range, the signal transmitted by the A/F sensor will be inaccurate, as a result, the ECM will be unable to regulate air fuel ratio properly.
5 When the current in the A/F sensor heater is outside the normal operating range, the ECM interprets this as a malfunction in the sensor heater and sets a DTC.
Example:
The ECM sets DTC P0032 or P0052 when the current in the A/F sensor heater is more than 10 A. Conversely, when the heater current is less than 0.8 A, DTC P0031 or P0051 is set.
MONITOR STRATEGY
TYPICAL ENABLING CONDITIONS
All:
P0031 and P0051:
P0032 and P0052:
TYPICAL MALFUNCTION THRESHOLDS
P0031 and P0051:
P0032 and P0052:
COMPONENT OPERATING RANGE
WIRING DIAGRAM
CONFIRMATION DRIVING PATTERN
1 Connect the Techstream to the DLC3.
2 Turn the engine switch on (IG).
3 Turn the Techstream on.
4 Clear DTCs DTC Check / Clear.
5 Start the engine, and warm it up until the ECT reaches 75°C (167°F) or higher (Procedure "A").
6 Select the following menu items: Powertrain / Engine and ECT / Data List / Idle Fuel Cut.
7 Drive the vehicle at between 38 mph (60 km/h) and 75 mph (120 km/h) for at least 10 minutes (Procedure "B").
8 Change the transmission to the 2nd gear (Procedure "C").
9 Drive the vehicle at a proper vehicle speed to perform fuel-cut operation (refer to the following HINT) (Procedure "D").
HINT:
Fuel-cut is performed when the following conditions are met:
- Accelerator pedal is fully released.
- Engine speed is 2500 rpm or more (fuel injection returns at 1000 rpm).
10 Accelerate the vehicle to 40 mph (64 km/h) or more by depressing the accelerator pedal for at least 10 seconds (Procedure "E").
11 Soon after performing procedure E above, release the accelerator pedal for at least 4 seconds without depressing the brake pedal, in order to execute fuel-cut control (Procedure "F").
12 Allow the vehicle to decelerate until the vehicle speed declines to less than 6 mph (10 km/h).
13 Repeat procedure from C through F above at least 3 times in one driving cycle.
HINT:
Completion of all A/F sensor monitors is required to change the value in Test Results.
CAUTION:
Strictly observe posted speed limits, traffic laws, and road conditions when performing these drive patterns.
INSPECTION PROCEDURE
HINT:
Read freeze frame data using the Techstream. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction Freeze Frame Data.
PROCEDURE
1. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)
(a) Disconnect the E74 or E70 A/F sensor connector.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance (Bank 1 sensor 1):
Standard resistance (Bank 2 sensor 1):
(c) Reconnect the A/F sensor connector.
NG -- REPLACE AIR FUEL RATIO SENSOR
OK -- Continue to next step.
2. CHECK TERMINAL VOLTAGE (+B OF A/F SENSOR)
(a) Disconnect the E74*1 or E70*2 A/F sensor connector.
HINT:
*1: Bank 1 sensor 1
HINT:
*2: Bank 2 sensor 1
(b) Turn the engine switch on (IG).
(c) Measure the voltage according to the value(s) in the table below.
Standard voltage (Bank 1 sensor 1):
Standard voltage (Bank 2 sensor 1):
(d) Reconnect the A/F sensor connector.
NG -- INSPECT FUSE (A/F)
OK -- Continue to next step.
3. CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM, ECM - BODY GROUND)
(a) Check the wire harness and the connector between the ECM and the A/F sensor, and ECM and body ground.
(1) Disconnect the E74 or E70 A/F sensor connector.
(2) Disconnect the E45 ECM connector.
(3) Measure the resistance according to the value(s) in the table below.
Standard resistance (Check for open):
Standard resistance (Check for short):
(4) Reconnect the A/F sensor connector.
(5) Reconnect the ECM connector.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- REPLACE ECM
4. INSPECT FUSE (A/F)
(a) Remove the A/F fuse from the No. 2 engine room relay block.
(b) Measure the resistance of the A/F fuse.
Standard resistance:
Below 1 Ohms
(c) Reinstall the A/F fuse.
NG -- CHECK FOR SHORT IN ALL HARNESSES AND CONNECTORS CONNECTED TO FUSE AND REPLACE FUSE
OK -- Continue to next step.
5. INSPECT A/F RELAY
(a) Remove the A/F relay from the No. 2 engine room relay block.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance:
(c) Reinstall the A/F relay.
NG -- REPLACE A/F RELAY
OK -- Continue to next step.
6. CHECK HARNESS AND CONNECTOR (A/F SENSOR - A/F RELAY, A/F RELAY - A/F FUSE)
(a) Check the wire harness and the connector between the A/F sensor, A/F fuse and A/F relay.
(1) Remove the A/F fuse and A/F relay from the No. 2 engine room relay block.
(2) Measure the resistance according to the value(s) in the table below.
Standard resistance (Check for open):
Standard resistance (Check for short):
(3) Reinstall the A/F fuse.
(4) Disconnect the E74 or E70 A/F sensor connector.
(5) Measure the resistance according to the value(s) in the table below.
Standard resistance (Check for open):
Standard resistance (Check for short):
(6) Reinstall the A/F relay.
(7) Reconnect the A/F sensor connector.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- REPAIR OR REPLACE HARNESS OR CONNECTOR (A/F FUSE - BATTERY)