Mazda RX-8 Manual page 681

DTC P0139
DTC P0139 Rear HO2S circuit slow response
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DETECTION
CONDITION
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POSSIBLE
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CAUSE
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The PCM monitors the rear HO2S inversion cycle period, lean-to-rich response time
and rich-to-lean response time when under the open loop fuel control (fuel cut off
control). If the average response time is more than the specification, the PCM
determines that the rear HO2S circuit response is slow.
Diagnostic support note
This is an intermittent monitor (HO2S).
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.
Purge solenoid valve malfunction
Looseness of rear HO2S
Leakage exhaust gas
Rear HO2S malfunction
Fuel line pressure malfunction
Leakage fuel
Fuel pump unit malfunction
AIR system malfunction
Leakage engine coolant
PCM malfunction
(w) Engine Diagnostics & Control
Page 118