DTC P0031: Ho2S Heater Control Circuit Low (Bank 1 Sensor 1)

OUTLINE OF DIAGNOSIS
Detect the open or short circuit of heater.

The heater conducts the duty control. The output terminal voltage at ON becomes 0 V, and the output terminal voltage at OFF becomes battery voltage.

Judge NG when the terminal voltage remains to be Low.
COMPONENT DESCRIPTION

Fig 1: Identifying HO2S Heater Control Circuit Low
Courtesy of SUBARU OF AMERICA, INC.

ENABLE CONDITION

ENABLE CONDITION CHART

Secondary Parameters	Enable Conditions
Battery voltage	"GREATER THAN EQUAL TO" 10.9 V

DIAGNOSTIC METHOD

Abnormality Judgment

Judge NG when the continuous time of completing the malfunction criteria below becomes more than 1 second (8 cycles).

Judgment Value

JUDGMENT VALUE CHART

Malfunction Criteria	Threshold Value
Output voltage level	Low
Front oxygen (A/F) sensor heater control duty	< 87.5%

Time Needed for Diagnosis: 1 second

Malfunction Indicator Light Illumination: Illuminates as soon as malfunction occurs.

Normality Judgment

Judge OK and clear the NG when all the malfunction criteria below are completed.

Judgment Value

JUDGMENT VALUE CHART

Malfunction Criteria	Threshold Value
Output voltage level	High

DTC CLEAR CONDITION
- When the OK idling cycle was completed 40 times in a row
- When "Clear Memory" was performed
MALFUNCTION INDICATOR LIGHT CLEAR CONDITION
- When the OK driving cycle was completed 3 times in a row
- When "Clear Memory" was performed
FAIL SAFE
- Front oxygen (A/F) sensor activation judgment: Front oxygen (A/F) sensor full activation is not complete, or front oxygen (A/F) sensor half activation is not complete.
- A/F main learning: Not allowed to calculate the A/F main learning compensation factor.
- Compensation when starting the engine at high temperature: Make the MIN value to be 0 from 0.3 normally.
- Purge control: Not allowed to purge.
ECM OPERATING AT DTC SETTING
Memorize the freeze frame data. (For test mode $02)