DTC P0139: Rear Ho2S Circuit Slow Response

Fig 1: DTC P0139 Detection Condition & Possible Causes Chart

Courtesy of MAZDA MOTORS CORP.

Diagnostic Procedure 

Fig 2: DTC P0139 Diagnostic Procedure Chart (Step 1-6)

Courtesy of MAZDA MOTORS CORP.

Fig 3: DTC P0139 Diagnostic Procedure Chart (Step 7-15)

Courtesy of MAZDA MOTORS CORP.