626 2.5L

WARNING: This page is about a different car, the 2001 Mazda Protege, 2001 Mazda Millenia, 2001 Mazda MX-5 Miata, 2001 Mazda MPV, and 2001 Mazda 626. However, it is still accessible from the selected car via links, so may be relevant.

Warm engine to normal operating temperature. Connect NGS scan tool to DLC-2. DLC-2 is located under left side of instrument panel, right of steering column. Using scan tool, access DIAGNOSTIC DATA LINK menu, and select PCM. Highlight and select PID/DATA MONITOR AND RECORD.
Turn ignition on. Select O2S11, O2S21, O2S12 or O2S22 PIDs to be checked and note voltage reading. See HO2S PID IDENTIFICATION (626 2.5L) table. See VOLTAGE/PID VALUE CHARTS article. If voltage is not as specified, check wiring harness and connector between PCM and HO2S. Also check intake manifold system, fuel system and self-diagnostic system. Repair as necessary. If no problems are present, replace suspect HO2S.
To test HO2S heating element, allow sensor to cool to room temperature. Disconnect HO2S 4-pin connector. Using ohmmeter, measure resistance between HO2S 4-pin connector terminals "C" and "D" for rear HO2S. See Fig 1 . Resistance should be about 6 ohms at 68°F (20° C). If resistance is not as specified, replace HO2S.

HO2S PID IDENTIFICATION (626 2.5L)

HO2S	PID
Right Front HO2S	O2S11
Left Front HO2S	O2S21
Right Rear HO2S	O2S12
Left Rear HO2S	O2S22

Fig 1: Identifying HO2S Terminals (626 2.5L)

Courtesy of MAZDA MOTORS CORP.