Hi There, I'm Clayso a certified master automobile technician with 30 years of automotive repair and diagnostic experience and I'm here to help with this problem. Additional services may be offered for detailed information.
P2096-Downstream Fuel Trim System 1 Lean
P2096 Sets when the downstream O2 sensor differs from the upstream O2 sensors before the converters to many time in a certain time frame. When the code goes away it means the problem is not present at the time. Several things could have caused this to happen. From a contaminate in the fuel to following to closely behind a diesel powered vehicle (maybe), a very slight exhaust leak. etc....
Anything that is burned in the combustion chambers of your vehicle is monitored by the O2 sensors. Whether it be sucked in through the intake or sprayed in from the fuel system, the oils crankcase through the crankcase ventilation. It's really hard to say what the actual cause that set the code unless the system was being monitored with a scan tool and the technician happen to catch the fail records on freeze frame of the scan tool. This is the short version of P2096. The long version is below.
The Oxygen sensors
(O2 sensor) are used for fuel control and catalyst monitoring. Each O2 sensor compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the O2 sensor signal voltage while calculating the air-to-fuel ratio. The heating elements inside each O2 sensor heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the PCM to calculate the air-to-fuel ratio sooner. While the engine runs, the O2 sensor heats up and begins to generate a voltage within a range of 0-1,275 mV. Once sufficient O2 sensor voltage fluctuation is observed by the PCM, Closed Loop is entered. The PCM uses the O2 sensor voltage to determine the air-to-fuel ratio. An O2 sensor voltage that increases toward 1,000 mV indicates a rich fuel mixture. An O2 sensor voltage that decreases toward 0 mV indicates a lean fuel mixture.
The conditions that cause this diagnostic to fail is when the upstream O2 sensor becomes biased from an exhaust leak, O2 sensor contamination or some other extreme operating condition. The downstream O2 sensor is considered to be protected from extreme environments by the catalyst. The PCM monitors the downstream O2 sensor feedback control, called downstream fuel trim, to detect any shift in the upstream O2 sensor target voltage from nominal target voltage. The value of the downstream fuel trim is compared with the lean thresholds. Every time the value exceeds the calibrated threshold, a fail timer is incremented and mass flow through the exhaust is accumulated. If the fail timer and accumulated mass flow exceed the fail thresholds, the test fails and the diagnostic stops running for that trip. If the test fails on consecutive trips, a Diagnostic Trouble Code (DTC) is set.
I hope this information is helpful to you.
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