P0031 HO2S Heater Control Circuit Low (Bank 1 / Sensor 1) - Automotive Repair Guides & Equipment

COMPONENT LOCATION

GENERAL DESCRIPTION

The normal operating temperature of the HO2S(Heated Oxygen Sensor) ranges from 350 to 850°C(662 to 1562°F). The HO2S heater greatly decreases the amount of time required for fuel control to become active. The ECM provides a pulse width modulated control circuit to adjust current through the heater. When the HO2S is cold, the value of the resistance is low and the current in the circuit is high. On the contrary, if the temperature in the resistor of the sensor rises, the current drops gradually.

DTC DESCRIPTION

If the ECM detects short to ground or open in heater under detecting conditions, ECM sets P0031.

possible causes

1.	Poor Connection

2.	Open in Power Circuit

3.	Open or short to ground in control circuit

4.	HO2S(B1/S1)

ECM

SPECIFICATION

Heater
Resistance (Ω)	3.3 ~ 4.1[20°C(68°F)]

DIAGNOSTIC CIRCUIT DIAGRAM

TERMINAL AND CONNECTOR INSPECTION

1.	Many malfunctions in the electrical system are caused by poor harness and terminals. Faults can also be caused by interference from other electrical systems, and mechanical or chemical damage.

2.	Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage.

Has a problem been found?

	▶ Repair as necessary .
	▶ Go to ” Power Circuit Inspection ” procedure.

POWER CIRCUIT INSPECTION

■ Check voltage

1.	IG “OFF” & Disconnect HO2S(B1/S1) connector.

IG “ON”.

Measure voltage between power terminal of HO2S(B1/S1) heater harness connector and chassis ground.

B+

Is the measured voltage within specification ?

	▶ Go to ” Control Circuit Inspection ” procedure.
	▶ Repair open or short to ground in HO2S(B1/S1) Heater power circuit.

CONTROL CIRCUIT INSPECTION

■ Check short to ground

1.	IG “OFF” & Disconnect HO2S(B1/S1) connector.

Measure resistance between control terminal of HO2S(B1/S1) heater harness connector and chassis ground.

Infinite

Is the measured resistance within specification ?

	▶ Go to “Check open in harness” procedure.
	▶ Repair short to ground in HO2S (B1/S1) heater control circuit.

■ Check open in harness

1.	IG “OFF” and disconnect HO2S(B1/S1) and ECM connector.

Measure resistance between control terminal of HO2S(B1/S1) heater harness connector and heater control terminal of ECM harness connector.

Approx. below 1Ω

Is the measured resistance within specification ?

	▶ Go to “Component Inspection” procedure.
	▶ Repair open in HO2S(B1/S1) heater control circuit .

COMPONENT INSPECTION

■ Check HO2S(B1/S1) Heater resistance

1.	IG “OFF” and disconnect HO2S(B1/S1) connector

Measure resistance between power and control terminals of HO2S(B1/S1) heater(Component Side)

3.3 ~ 4.1[20°C(68°F)]

Is the measured resistance within specification?

▶ Substitute with a known – good ECM and check for proper operation.

There is a memory reset function on GDS that can erase optional parts automatically detected and memorized by ECM. Before or after testing ECM on the vehicle, use this function to reuse the ECM on the others

▶ Substitute with a known – good HO2S and check for proper operation. If the problem is corrected.

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