P0140 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat

OBD-II Trouble Shooting Got a code reader? Find out what your GM car's Check Engine light is trying to tell you (and then turn Check Engine light off).

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Old 09-24-2009, 11:13 AM   #1
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Default P0140



Three-Way Catalyst (TWC) system is used to control emissions.
PCM uses signal from Heated Oxygen Sensor (HO2S) behind TWC to read
efficiency of TWC. PCM will set DTC P0140 if TWC oxygen storage
capacity is less than a predetermined threshold.

Your Service engine light(SES), or malfuction indicator lamp (MIL) will be illuminated. There will not likely be any noticeable drivability problems other than the MIL. The rear or post catalytic converter Oxygen sensor does not affect fuel deliver It only MONITORS the efficiency of the catalytic converter.

  • Shorted heater circuit in O2 sensor.
  • Shorted signal circuit in O2 sensor
  • Melting of harness connector or wiring due to touching the exhaust system
  • Water in harness connector or PCM connector
  • Bad PCM
Possible Solutions
Typically, simply changing the rear O2 sensor corrects the problem. Before doing this inspect the wires and connectors for damage or corrosion.
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