Front exhaust manifold, approximately 8-12 inches downstream from cylinder head exhaust ports, before catalytic converter. Bank 1 is the only bank on this inline 4-cylinder engine
Pins
4-pin connector
0
Timebase
1s/div for monitoring fuel trim response
Voltage Scale
500mV/div centered on 3.3V
Trigger
Not applicable
Wiring
Four-wire configuration: Two heater wires (White wires, typically 12V supply and ground), IP signal wire (Black wire - positive current control), VS/COM signal wire (Gray wire - reference voltage approximately 3.3V)
Expected Voltage Range
At Idle
3V to 3.6V
At Higher RPM
2.8V to 3.8V
Expected Pattern
Relatively stable DC voltage around 3.3V with small fluctuations (±0.2V) during closed-loop operation. Wideband AFR sensors maintain near-constant voltage with current modulation for mixture detection, unlike switching narrowband sensors
Known-Good Waveform
Stable voltage output centered at approximately 3.3V (reference voltage) with minimal deviation during steady-state cruise. Unlike narrowband sensors, this wideband AFR sensor does not switch rapidly but maintains relatively constant voltage while the ECU monitors current flow through the sensor to determine precise air-fuel ratio. During fuel cut on deceleration, voltage may shift slightly toward lean indication (3.1-3.2V). During enrichment for acceleration, expect slight shift toward rich (3.4-3.5V).
Common Failure Patterns
Voltage fixed at approximately 3.3V with no response to mixture changes, or reading stuck at 0V or 5V
Cause: Failed sensor element due to silicon contamination from oil consumption or coolant entering combustion chamber, common on engines with worn piston rings or valve seals
Erratic voltage fluctuations exceeding ±0.5V or noisy signal with rapid oscillations
Cause: Exhaust leak upstream of sensor allowing unmetered air to enter exhaust stream, or damaged sensor wiring from heat exposure near exhaust manifold
The 2019-2024 RAV4 2.5L uses Denso wideband AFR sensors. Monitor voltage using enhanced scan data rather than oscilloscope as the meaningful data is current-based. Check sensor heater operation with amp clamp; should draw 6-8A initially then drop to 2-3A when at operating temperature within 30 seconds of cold start.
Related Diagnostic Trouble Codes
P0130P0131P0132P0133P0134
Always confirm waveform data with your vehicle's OEM service manual before diagnosing.