Bank 1 (front cylinder bank), after three-way catalytic converter in underbody position, approximately mid-vehicle underneath driver's seat area
Pins
4-pin connector
Idle Frequency
0.2 Hz
Timebase
5s/div to observe slow response
Voltage Scale
200mV/div
Trigger
Not applicable, use normal mode
Wiring
White (heater +), Brown (heater -), Black (signal ground), Gray (signal output)
Expected Voltage Range
At Idle
0.6V to 0.9V
At Higher RPM
0.1V to 0.9V
Expected Pattern
Relatively flat voltage centered around 0.65-0.75V with very slow, lazy fluctuations (0.1-0.5 Hz) indicating catalytic converter is buffering oxygen content. Should NOT show rapid switching like upstream sensor. Amplitude typically less than 0.3V peak-to-peak.
Known-Good Waveform
Waveform should appear relatively flat or show very slow, gentle transitions between 0.6-0.8V, indicating the catalytic converter is properly storing and releasing oxygen. Fluctuations should be infrequent (less than once per second) and smooth. A healthy catalyst will dampen the rapid switching seen at the upstream sensor, resulting in a stable downstream reading that proves converter efficiency.
Common Failure Patterns
Rapid switching pattern similar to upstream sensor, voltage alternating between 0.1-0.9V more than 1 time per second, mimicking pre-cat sensor behavior
Post-cat sensor monitors catalytic converter efficiency on the 2GR-FKS. Compare upstream and downstream waveforms simultaneously - the downstream should be much slower and flatter. During active fuel trim tests (forced rich/lean), the downstream should respond slowly compared to upstream. Underbody location makes this sensor susceptible to road salt corrosion on connectors.
Related Diagnostic Trouble Codes
P0136P0137P0138P0139P0140
Always confirm waveform data with your vehicle's OEM service manual before diagnosing.