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P0137 on Toyota 4Runner

O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2)

Factory diagnostic protocol and troubleshooting wire for fault code P0137 specifically for the Toyota 4Runner (2020–2026, 4.0L V6 (1GR-FE) / 2.4L i-FORCE Turbo 4-Cyl).

Verified OEM Telemetry & Field Repair Tree
Toyota 4Runner2020–2026
Toyota 4Runner
SUV4.0L V6 (1GR-FE) / 2.4L i-FORCE Turbo 4-Cyl
Reliability
Sensor Voltage Ref
0.1V – 5.0V Ref
4Runner SAE Mode $01
ECU Network Bus
500 kbps CAN-FD
ISO 15765-4 Compliant
Drivability Status
Drivable (Short Trip)
Low urgency level
Est. Repair Cost
$100 - $300 (DIY: $35 - $100)
Parts & Labor DIY
Check P0137 On Another Toyota Model:
Diagnose P0137 on Specific 4Runner Model Year:

1. Symptoms of P0137 on Toyota 4Runner

When the Engine Control Module (ECM/PCM) on your Toyota 4Runner (4.0L V6 (1GR-FE) / 2.4L i-FORCE Turbo 4-Cyl) logs fault code P0137, drivers commonly observe:

Check Engine Light on on Toyota 4Runner (4.0L V6 (1GR-FE) / 2.4L i-FORCE Turbo 4-Cyl)
Downstream sensor voltage consistently below 0.15V on scan tool on Toyota 4Runner (4.0L V6 (1GR-FE) / 2.4L i-FORCE Turbo 4-Cyl)
Failed emissions test on Toyota 4Runner (4.0L V6 (1GR-FE) / 2.4L i-FORCE Turbo 4-Cyl)
Toyota 4Runner OBD-II Port Location
The 16-pin diagnostic connector is located Lower dashboard near parking brake mechanism. Plug in your scan tool to verify freeze-frame sensor values.

2. Most Likely Causes on Toyota 4Runner

Historical warranty claims and technical repair bulletins for Toyota 4Runner point to the following failure distribution:

55%
Exhaust leak upstream of or directly at the Sensor 2 bung letting in fresh air (Toyota OEM Part)
25%
Faulty downstream oxygen sensor (Toyota OEM Part)
12%
Short to ground in sensor signal wire (Toyota OEM Part)
8%
Extremely lean exhaust condition (Toyota OEM Part)
* Source: Synthesized from NHTSA ODI field repair telemetry and verified OEM Technical Service Bulletin (TSB) repair tree frequency percentiles for Toyota 4Runner.

3. Step-by-Step DIY Repair Guide for Toyota 4Runner

01
Inspect Exhaust System for Leaks

Listen for exhaust ticking or black soot around flex pipe, flanges, and sensor bungs before the catalytic converter. on the Toyota 4Runner equipped with 4.0L V6 (1GR-FE) / 2.4L i-FORCE Turbo 4-Cyl.

Required Tool: Flashlight, Jack Stands
02
Check Sensor Signal Voltage with Scan Tool

Monitor B1S2 voltage. Snap the throttle to enrich mixture; voltage should briefly spike above 0.8V. If it remains 0.0V–0.1V, sensor is defective or shorted. on the Toyota 4Runner equipped with 4.0L V6 (1GR-FE) / 2.4L i-FORCE Turbo 4-Cyl.

Required Tool: OBD-II Scanner
03
Replace Downstream O2 Sensor

Unplug harness, remove old sensor with 7/8 socket, install replacement sensor and plug firmly. on the Toyota 4Runner equipped with 4.0L V6 (1GR-FE) / 2.4L i-FORCE Turbo 4-Cyl.

Required Tool: O2 Sensor Socket, Ratchet
04
Clear Codes

Clear DTCs and verify B1S2 holds steady between 0.45V and 0.75V during steady highway cruising. on the Toyota 4Runner equipped with 4.0L V6 (1GR-FE) / 2.4L i-FORCE Turbo 4-Cyl.

Required Tool: OBD-II Scanner
Recommended Parts & Testing Tools

Equipment for Diagnosing Toyota 4Runner (P0137)

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Toyota 4Runner OEM Replacement Sensor

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Direct-fit replacement assembly engineered to OEM tolerances for Toyota 4Runner.

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Sensor Signal Voltage Meter

AstroAI Auto-Ranging Digital Multimeter

4.6 / 5.0 (Best Seller)

Essential for testing 0.1V–5.0V sensor reference signals, ground continuity (<0.20Ω), and harness resistance.

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BlueDriver Bluetooth Pro OBDII Scan Tool

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Reads and clears enhanced codes (ABS, Airbag, Transmission, Engine) & live freeze-frame telemetry on phone.

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Other Common Fault Codes on Toyota 4Runner

Frequently diagnosed powertrain, emissions, and sensor trouble codes logged on the Toyota 4Runner:

4. Toyota 4Runner P0137 FAQs

What causes code P0137 to trigger on a Toyota 4Runner?

On the Toyota 4Runner (4.0L V6 (1GR-FE) / 2.4L i-FORCE Turbo 4-Cyl), P0137 is most frequently caused by Exhaust leak upstream of or directly at the Sensor 2 bung letting in fresh air or Faulty downstream oxygen sensor.

Where is the OBD-II port located on my Toyota 4Runner?

On the Toyota 4Runner, the 16-pin DLC diagnostic connector is located Lower dashboard near parking brake mechanism. Plug in any standard OBD-II scanner with the ignition in the ON position to read freeze-frame parameters.

Can I safely drive my Toyota 4Runner with code P0137?

Yes. Vehicle is fully drivable, but Check Engine Light will remain illuminated. Given that P0137 carries a Low severity rating, we advise avoiding heavy towing or aggressive throttle inputs until sensor readings are verified.