Troubleshooting

DTC P0038 OXYGEN SENSOR HEATER CONTROL CIRCUIT HIGH (BANK 1 SENSOR 2)

CIRCUIT DESCRIPTION

DTC Detection Condition:

The heated oxygen sensor (HO2S) is the lamination type. Compared to the conventional type, the sensor and heater portions of the lamination type are narrower overall. Because the heat of the heater acts directly on the alumina and zirconia (of the sensor portion) it accelerates the activation of the sensor.

The heated oxygen sensor is used to monitor oxygen concentration in the exhaust. For optimum catalytic converter operation, the air fuel mixture must be maintained near the ideal stoichiometric air fuel ratio. The oxygen sensor output voltage changes at the stoichiometric ratio. The ECM adjusts the fuel injection time so that the air fuel ratio is nearly stoichiometric.

If the oxygen concentration in the exhaust gas increases, the air fuel ratio is called LEAN. The heated oxygen sensor voltage drops below 0.45 V, which informs the ECM of the LEAN condition.

If oxygen is not in the exhaust gas, the air fuel ratio is called RICH. The heated oxygen sensor voltage increases above 0.45 V, which informs the ECM of the RICH condition.

The heated oxygen sensors include 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), current flows to the heater in order to heat the sensor for the accurate oxygen concentration detection.

HINT: The ECM provides a pulse width modulated control circuit to adjust current through the heater. The heated oxygen sensor heater circuit uses a relay on the B+ side of the circuit.

HINT:
- Bank 1 refers to the bank that includes cylinder No.1.
- Bank 2 refers to the bank that does not include cylinder No.1.
- 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

Monitor Strategy:

Typical Enabling Conditions:

Typical Malfunction Thresholds:

Component Operating Range:

Monitor Result (Mode 06 Data):

The sensing portion of the heated oxygen sensor has a zirconia element which is used to detect oxygen concentration in the exhaust. If the zirconia element is at the proper temperature and difference of the oxygen concentration between the inside and outside surface of sensor is large, the zirconia element will generate voltage signals. In order to increase the oxygen concentration detecting capacity in the zirconia element, the ECM supplements the heat from the exhaust with heat from a heating element inside the sensor. When current in the sensor is out of the standard operating range, the ECM interprets this as a fault in the heated oxygen sensor and sets a DTC.

Example:
The ECM will set a high current DTC if the current in the sensor is more than 2 A when the heater is OFF. Similarly, the ECM will set a low current DTC if the current is less than 0.25 A when the heater is ON.

Wiring Diagram:

Step 1:

Step 2 - 3:

Step 4:

INSPECTION PROCEDURE

HINT:
- If different DTCs that are related to a different system are output simultaneously while terminal E2 is used as a ground terminal, terminal E2 may be open.
- Read freeze frame data using the hand-held tester or the OBD II scan tool. Freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, 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.