DTC P0031 [13B-MSP]

DTC REFERENCE CHART

DTC P0031	A/F sensor heater control circuit low input
DETECTION CONDITION	The input voltage to the A/F sensor heater drive terminal in the PCM is at the set value or less for 1 s or more even though the A/F sensor heater is duty-controlled at under 90% by the PCM. Diagnostic support note This is a continuous monitor (A/F sensor heater, HO2S heater.) The MIL illuminates if the PCM detects the above malfunction condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM. PENDING CODE is available if the PCM detects the above malfunction condition during the first drive cycle. FREEZE FRAME DATA is available. The DTC is stored in the PCM memory.
POSSIBLE CAUSE	Connector or terminal malfunction Open circuit in wiring harness between main relay terminal C and A/F sensor terminal C Short to ground in wiring harness between main relay terminal C and A/F sensor terminal C Short to ground in wiring harness between A/F sensor terminal D and PCM terminal 2BG Open circuit in wiring harness between A/F sensor terminal D and PCM terminal 2BG A/F sensor heater malfunction PCM malfunction
Courtesy of MAZDA MOTORS CORP.

DTC P0031

A/F sensor heater control circuit low input

DETECTION CONDITION

The input voltage to the A/F sensor heater drive terminal in the PCM is at the set value or less for 1 s or more even though the A/F sensor heater is duty-controlled at under 90% by the PCM.

Diagnostic support note

This is a continuous monitor (A/F sensor heater, HO2S heater.)
The MIL illuminates if the PCM detects the above malfunction condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM.
PENDING CODE is available if the PCM detects the above malfunction condition during the first drive cycle.
FREEZE FRAME DATA is available.
The DTC is stored in the PCM memory.

POSSIBLE CAUSE

Connector or terminal malfunction
Open circuit in wiring harness between main relay terminal C and A/F sensor terminal C
Short to ground in wiring harness between main relay terminal C and A/F sensor terminal C
Short to ground in wiring harness between A/F sensor terminal D and PCM terminal 2BG
Open circuit in wiring harness between A/F sensor terminal D and PCM terminal 2BG
A/F sensor heater malfunction
PCM malfunction

Courtesy of MAZDA MOTORS CORP.

DIAGNOSTIC PROCEDURE

STEP	INSPECTION		ACTION
1	VERIFY FREEZE FRAME DATA AND DIAGNOSTIC MONITORING TEST RESULTS HAVE BEEN RECORDED Have FREEZE FRAME DATA and DIAGNOSTIC MONITORING TEST RESULTS (A/F sensor heater, HO2S heater related) been recorded?	Yes	Go to the next step.
1		No	Record the FREEZE FRAME DATA and DIAGNOSTIC MONITORING TEST RESULTS on the repair order, then go to the next step.
2	VERIFY RELATED REPAIR INFORMATION AVAILABILITY Verify related Service Bulletins and/or on-line repair information availability. Is any related repair information available?	Yes	Perform repair or diagnosis according to the available repair information. If the vehicle is not repaired, go to the next step.
2		No	Go to the next step.
3	INSPECT A/F SENSOR CONNECTOR FOR POOR CONNECTION Turn the ignition switch off. Disconnect the A/F sensor connector. Inspect for poor connection (such as damaged/pulled-out pins, and corrosion.) Is there any malfunction?	Yes	Repair or replace the terminal, then go to Step 9.
3		No	Go to the next step.
4	INSPECT A/F SENSOR HEATER POWER CIRCUIT FOR OPEN CIRCUIT OR SHORT TO GROUND Turn the ignition switch to the ON position (engine off.) Measure the voltage between A/F sensor terminal C (wiring harness-side) and body ground. Is the voltage B+ ?	Yes	Go to the next step.
4		No	Repair or replace the wiring harness for a possible open circuit or short to ground, then go to Step 9.
5	INSPECT A/F SENSOR HEATER CONTROL CIRCUIT FOR SHORT TO GROUND Turn the ignition switch off. Inspect for continuity between A/F sensor terminal D (wiring harness-side) and body ground. Is there continuity?	Yes	Repair or replace the wiring harness for a possible short to ground, then go to Step 9.
5		No	Go to the next step.
6	INSPECT A/F SENSOR HEATER CONTROL CIRCUIT FOR OPEN CIRCUIT Turn the ignition switch off. Inspect for continuity between A/F sensor terminal D (wiring harness-side) and PCM terminal 2BG (wiring harness-side.) Is there continuity?	Yes	Go to the next step.
6		No	Repair or replace the wiring harness for a possible open circuit, then go to Step 9.
7	INSPECT PCM CONNECTOR FOR POOR CONNECTION Turn the ignition switch off. Disconnect the PCM connector. Inspect for poor connection (such as damaged/pulled-out pins, and corrosion.) Is there any malfunction?	Yes	Repair or replace the terminal, then go to Step 9.
7		No	Go to the next step.
8	INSPECT A/F SENSOR HEATER Inspect the A/F sensor heater. (See AIR FUEL RATIO (A/F) SENSOR INSPECTION [13B-MSP] .) Is there any malfunction?	Yes	Replace the A/F sensor, then go to the next step. (See AIR FUEL RATIO (A/F) SENSOR REMOVAL/INSTALLATION [13B-MSP] .)
8		No	Go to the next step.
9	VERIFY TROUBLESHOOTING OF DTC P0031 COMPLETED Make sure to reconnect all disconnected connectors. Clear the DTC from the PCM memory using the M-MDS. Perform the DRIVE MODE 3. (See OBD-II DRIVE MODE [13B-MSP] .) Is the PENDING CODE same as the DTC present?	Yes	Replace the PCM, then go to the next step. (See PCM REMOVAL/INSTALLATION [13B-MSP] .)
9		No	Go to the next step.
10	VERIFY AFTER REPAIR PROCEDURE Perform the "AFTER REPAIR PROCEDURE". (See AFTER REPAIR PROCEDURE [13B-MSP] .) Are any DTCs present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE [13B-MSP] .)
10		No	DTC troubleshooting completed.