Heated Oxygen Sensor Ho2S Signals (V6 Only)

DTC P1128 DETECTION CONDITION & POSSIBLE CAUSES

DTC P1128	HEATED OXYGEN SENSOR (HO2S) SIGNALS
DETECTION CONDITION	P1128 indicates that during KOER testing the front HO2S signal(s) response for a fuel shift to the correct engine bank was not indicated.
POSSIBLE CAUSE	Crossed HO2S harness connectors Crossed wiring at HO2S harness connectors Crossed wiring at 104-pin powertrain control module (PCM) harness connector Poor terminal connection
HINT	HO2S Sensor Description Detects the presence of oxygen in the exhaust and produces a variable voltage (0.0-1.1V) 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 0.4V). A low concentration of oxygen (rich air/fuel ratio) in the exhaust produces a high voltage signal (greater than 0.6V). 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.
Courtesy of MAZDA MOTORS CORP.
Courtesy of MAZDA MOTORS CORP.

DTC P1128 DIAGNOSTIC PROCEDURE

DTC P1128		HEATED OXYGEN SENSOR (HO2S) SIGNALS
STEP	INSPECTION		ACTION
1	Was the PCM quick test performed?	Yes	Go to next step.
1	Was the PCM quick test performed?	No	Perform PCM quick test. See PCM QUICK TEST .
2	KOER DTC P1128 Visually inspect vehicle front HO₂ S harness connector(s) for any indication of being crossed (stretched wires, wire harnesses not mounted properly). Are there crossed connections or wires?	Yes	Repair as necessary. Go to step 4.
2		No	Go to next step.
3	VERIFY PROPER HO2S SIG PIN LOCATION Disconnect PCM. Install breakout box, leave PCM disconnected. Disconnect both of the front HO2S from the vehicle harness connector. HO2S-11 (Front RH) = test pin 60 HO2S-21 (Front LH) = test pin 87 Measure the resistance of HO2S signal circuits between PCM test pins and HO2S harness connector. Is the resistance less than 5.0 ohms?	Yes	Unable to duplicate or identify at this time. See GENERAL PINPOINT TEST 4: INTERMITTENT .
3		No	Reconnect HO2S connector to proper HO2S signal pins in the PCM 104-pin harness or HO₂ S harness connectors. Go to next step.
4	VERIFY TROUBLESHOOTING OF DTCs COMPLETED Connect all disconnected connectors. Clear DTCs from PCM memory using WDS or equivalent tester. Perform PCM quick test. Is the same DTC present?	Yes	Replace PCM. See POWERTRAIN CONTROL MODULE (PCM) REMOVAL / INSTALLATION . Repeat PCM quick test.
4		No	If any other DTC is present, go to applicable DTC inspection. See DIAGNOSTIC TROUBLE CODE (DTC) INDEX - POWERTRAIN CONTROL MODULE (PCM) . If no DTC is present, troubleshooting is complete.