Heated Oxygen Sensor (Ho2S)

DTC P0131, P0151 DETECTION CONDITION AND POSSIBLE CAUSE

DTC P0131, P0151	HEATED OXYGEN SENSOR (HO2S)
DETECTION CONDITION	P0131 indicates HO2S-11 (Front RH) has generated a negative voltage. P0151 indicates HO2S-21 (Front LH) has generated a negative voltage.
POSSIBLE CAUSE	Contaminated HO2S (water, fuel etc.). Crossed HO2S signal/signal return wiring.
HINT	HO2S Sensor Description Detects the presence of oxygen in the exhaust and produces a variable voltage (0.0 -1.1 V) according to the amount of oxygen detected. A high concentration of oxygen (lean air/fuel ratio) in the exhaust produces a low voltage signal (less than 0.4 V). A low concentration of oxygen (rich air/fuel ratio) in the exhaust produces a high voltage signal (greater than 0.6 V). Provides feedback to the PCM indicating air/fuel ratio in order to achieve a near stoichiometric air/fuel ratio of 14.7:1 during closed loop engine operation.
Courtesy of MAZDA MOTORS CORP.

DTC P0131, P0151 INSPECTION

STEP	INSPECTION		ACTION
1	Was PCM Quick Test performed?	Yes	Go to next step.
1	Was PCM Quick Test performed?	No	Perform PCM Quick Test.
2	DTCS P0131 AND P0151: CONTAMINATED HO2S/VOLTAGE SHIFT NOTE: DTC P0131 = HO2S-11 (Front RH) and DTC P0151 = HO2S-21 (Front LH) Check for water in HO2S connector. Is there water in the HO2S connector?	Yes	Repair source of water entry. Dry out connector. Replace sensor. See HEATED OXYGEN SENSOR (HO2S) in REMOVAL, OVERHAUL, AND INSTALLATION article in Engine Performance . Go to step 4.
2		No	Go to next step.
3	VERIFY WIRING IS IN PROPER PIN LOCATION Disconnect PCM. Install Breakout Box, leave PCM disconnected. Measure resistance of the HO2S SIG circuit between PCM test pin 60 (DTC P0131) or PCM test pin 87 (DTC P0151) and the HO2S sensor harness connector. Measure resistance of the SIG RTN circuit between PCM test pin 91 and the HO2S sensor harness connector. Is each resistance less than 5.0 ohms?	Yes	Replace sensor. See HEATED OXYGEN SENSOR (HO2S) in REMOVAL, OVERHAUL, AND INSTALLATION article in Engine Performance . Go to step 4.
3		No	Repair wiring as necessary. Go to step 4.
4	VERIFY TROUBLESHOOTING OF DTCs COMPLETED Make sure to reconnect all disconnected connectors. Clear DTCs from PCM memory using NGS tester generic OBD-II function. Perform PCM Quick Test. Is same DTC present?	Yes	Replace PCM. See COMPUTERIZED ENGINE CONTROLS . Repeat PCM Quick Test.
4		No	If any other DTC is present, go to applicable DTC inspection. If no DTC is present, troubleshooting complete.

DTC P0136, P0156, P1137, P1138 DETECTION CONDITION AND POSSIBLE CAUSE

DTC P0136, P0156, P1137, P1138	HEATED OXYGEN SENSOR (HO2S)
DETECTION CONDITION	P0136 indicates the output voltage of the rear HO2S fails to meet the calibrated limits (Bank 1). P0156 indicates the output voltage of the rear HO2S fails to meet the calibrated limits (Bank 2). P1137 and P1138 indicate the rear HO2S is forced rich and lean by the PCM. The test fails if the PCM does not detect the rich signal (P1137) or lean signal (P1138) during KOER Self Test.
POSSIBLE CAUSE	Wiring concerns: Pinched, shorted, and corroded wiring and pins. Crossed sensor wires. Other concerns: Exhaust leaks. Contaminated or damaged sensor.
HINT	HO2S Sensor Description Detects the presence of oxygen in the exhaust and produces a variable voltage (0.0 -1.1 V) according to the amount of oxygen detected. A high concentration of oxygen (lean air/fuel ratio) in the exhaust produces a low voltage signal (less than 0.4 V). A low concentration of oxygen (rich air/fuel ratio) in the exhaust produces a high voltage signal (greater than 0.6 V). Provides feedback to the PCM indicating air/fuel ratio in order to achieve a near stoichiometric air/fuel ratio of 14.7:1 during closed loop engine operation.
Courtesy of MAZDA MOTORS CORP.

DTC P0136, P0156, P1137, P1138 INSPECTION

STEP	INSPECTION		ACTION
1	Was PCM Quick Test performed?	Yes	If Continuous Memory Ignition (P0350-P0354) or Misfire (P0300-P0306) DTCs are received during Continuous Memory Testing, repair them first. Otherwise, go to next step.
1	Was PCM Quick Test performed?	No	Perform PCM Quick Test.
2	CHECK FOR HO2S KOER Were DTCs P1137 or P1138 present during PCM Quick Test?	Yes	Go to next step.
2		No	The fault that produced the DTC P0136 or P0156 is intermittent. See TEST 4: INTERMITTENT .
3	VISUAL INSPECTION Checked for pinched, corroded and/or stretched wires. NOTE: Any exhaust leaks between the engine and the end of the catalyst can cause DTC P0136 or P0156 with P1137 and/or P1138. Inspect the following: Check for punctures and cracks in catalyst and pipes leading to them. Check exhaust flanges for leaks. Check HO2S torque. Are any of the listed possible causes present?	Yes	Repair as necessary. Go to step 10.
3		No	Go to next step.
4	CHECK HO2S HARNESS FOR SHORT TO VPWR AND GROUND Disconnect NGS Tester from DLC. Disconnect PCM. Install Breakout Box, leave PCM disconnected. Disconnect rear HO2S. Measure resistance between PCM test pin 35 and the following PCM test pins: 91 (short to SIG RTN). 71 (short to VPWR). 90 (short to VREF). 103 (short to PWR GND). Is each resistance greater than 10K ohms?	Yes	Go to next step.
4		No	Repair short in harness. Go to step 10.
5	CHECK RESISTANCE OF HO2S SIG AND GROUND CIRCUITS FOR OPEN IN HARNESS Measure resistance of HO2S SIG circuit between PCM test pin 35 and the HO2S harness connector. Measure resistance of HO2S SIG RTN circuit between PCM test pin 91 and the HO2S harness connector. Is the resistance reading less than 5.0 ohms?	Yes	Go to next step.
5		No	Repair open circuit. Go to step 10.
6	CHECK HO2S CIRCUIT VOLTAGE Remove Breakout Box. Reconnect PCM and rear HO2S. Reconnect NGS Tester. Key ON, Engine OFF (KOEO). Access the O2S12 PID with NGS Tester and note the voltage. Was the voltage greater than 1.5 V?	Yes	Go to step 9.
6		No	Go to next step.
7	CHECK RESISTANCE OF HO2S GROUND CIRCUIT IN THE PCM Key OFF. Disconnect PCM. Install Breakout Box and connect PCM to Breakout Box. Leave vehicle harness disconnected from Breakout Box. Measure resistance between PCM test pins 91 (SIG RTN) and PCM test pin 103 (PWR GND). Is the resistance less than 5.0 ohms?	Yes	Go to step 8.
7		No	Replace PCM. See COMPUTERIZED ENGINE CONTROLS . Go to step 10.
8	APPLY 12 VOLTS TO REAR HO2S CIRCUIT Remove Breakout Box. Connect PCM. Disconnect rear HO2S. Jumper VPWR to HO2S SIG at the vehicle harness connector. Key ON, Engine OFF (KOEO). Access O2S12 PID and monitor. Is the PID value greater than 1.5 V?	Yes	Replace rear HO2S. See HEATED OXYGEN SENSOR (HO2S) in REMOVAL, OVERHAUL, AND INSTALLATION article in Engine Performance . Go to step 10.
8		No	Replace PCM. See COMPUTERIZED ENGINE CONTROLS . Go to step 10.
9	CHECK FOR OVER VOLTAGE ON THE HO2S CIRCUIT IN THE PCM Key ON, Engine OFF (KOEO). Disconnect rear HO2S. Measure voltage between SIG RTN circuit at the HO2S vehicle harness connector and battery negative post. Measure voltage between HO2S SIG circuit at the HO2S vehicle harness connector and battery negative post. Are the voltage readings greater than 1.5 V?	Yes	Replace PCM. See COMPUTERIZED ENGINE CONTROLS . Go to step 10.
9		No	Replace rear HO2S. See HEATED OXYGEN SENSOR (HO2S) in REMOVAL, OVERHAUL, AND INSTALLATION article in Engine Performance . Go to step 10.
10	VERIFY TROUBLESHOOTING OF DTCs COMPLETED Make sure to reconnect all disconnected connectors. Clear DTCs from PCM memory using NGS tester generic OBD-II function. Perform PCM Quick Test. Is same DTC present?	Yes	Replace PCM. See COMPUTERIZED ENGINE CONTROLS . Repeat PCM Quick Test.
10		No	If any other DTC is present, go to applicable DTC inspection. If no DTC is present, troubleshooting complete.