P0051
1GR-FE 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 say 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 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 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.
HINT:
- 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 Voltage B1S1 or AFS Voltage B2S1.
- 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 voltage output cannot be confirmed without using the Techstream.
- If a A/F sensor malfunction is detected, the ECM sets a DTC.
HINT:
- When either 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 ignition switch is turned to OFF.
- Although the DTC titles say the 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 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
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.
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.
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.
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 becomes inaccurate, as a result, the ECM is unable to regulate air-fuel ratio properly.
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.
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
INSPECTION PROCEDURE
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. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)
(a) Disconnect the D33*1 or D34*2 A/F sensor connector.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance (for Bank 1 sensor 1):
Standard resistance (for Bank 2 sensor 1):
NG -- REPLACE AIR FUEL RATIO SENSOR
OK -- Continue to next step.
2. CHECK TERMINAL VOLTAGE (+B OF A/F SENSOR)
(a) Disconnect the D33*1 or D34*2 A/F sensor connector.
(b) Measure the resistance according to the value(s) in the table below.
Standard voltage (for Bank 1 sensor 1):
Standard voltage (for Bank 2 sensor 1):
NG -- INSPECT INTEGRATION RELAY (A/F RELAY)
OK -- Continue to next step.
3. CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM)
(a) Disconnect the D33*1 or D34*2 A/F sensor connector.
(b) Disconnect the D74 ECM connector.
(c) Measure the resistance according to the value(s) in the table below.
Standard resistance (Check for open):
Standard resistance (Check for short):
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- Continue to next step.
4. CHECK WHETHER DTC OUTPUT RECURS
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch ON.
(c) Turn the Techstream ON.
(d) Clear DTCs DTC Check / Clear.
(e) Start the engine.
(f) Allow the engine to idle for 1 minute or more.
(g) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
(h) Read the DTCs.
Result:
B -- REPLACE ECM
A -- CHECK FOR INTERMITTENT PROBLEMS
5. INSPECT INTEGRATION RELAY (A/F RELAY)
(a) Remove the integration relay from the engine room junction block Testing and Inspection.
(b) Inspect the A/F fuse.
(1) Remove the A/F fuse from the integration relay.
(2) Measure the resistance according to the value(s) in the table below.
Standard resistance:
(3) Reinstall the A/F fuse.
(c) Inspect the A/F relay.
(1) Measure the resistance according to the value(s) in the table below.
Standard resistance:
NG -- REPLACE INTEGRATION RELAY
OK -- Continue to next step.
6. CHECK HARNESS AND CONNECTOR (A/F SENSOR - A/F SENSOR HEATER RELAY (A/F))
(a) Disconnect the D33*1 or D34*2 A/F sensor heater relay (A/F) connector.
HINT: *1: Bank 1 sensor 1
*2: Bank 2 sensor 1
(b) Remove the integration relay from the engine room junction block Testing and Inspection.
(c) Measure the resistance according to the value(s) in the table below.
Standard resistance (Check for open):
Standard resistance (Check for short):
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- CHECK ECM POWER SOURCE CIRCUIT