OBD-II Fault Code Guide

P0137 Code: O2 Sensor Circuit Low Voltage
Bank 1, Sensor 2 – Causes, Symptoms & Fix

Published: August 23, 2025 Last Updated: May 6, 2026 Verified by iCarsoft Tech Team 12 min read
Quick Summary

P0137 means the downstream oxygen sensor on Bank 1 (Sensor 2) is reading abnormally low voltage — below 0.4V for 20+ seconds. The most common fix is replacing the downstream O2 sensor ($50–$150 DIY) or repairing a damaged wiring connector. You can drive short distances, but prolonged driving risks catalytic converter damage worth $500–$1,500. Always use live data to confirm the root cause before replacing any parts.

P0137 — Quick Reference
Definition O2 Sensor Circuit Low Voltage — Bank 1, Sensor 2
Severity Moderate–High — MIL on, emissions failure, converter risk
Trigger Sensor voltage < 0.4V for 20+ seconds
Location After catalytic converter, Bank 1 (cylinder #1 side)
Common Vehicles Toyota, Honda, Ford, Chevrolet, Vauxhall/Opel
Related Codes P0136, P0138, P0141, P0420, P0157
DIY Fix Cost $50–$150 (O2 sensor only)
Pro Fix Cost $150–$600 sensor; $500–$1,500 converter
Recommended Tool iCarsoft CR MAX BT
iCarsoft CR MAX BT scanning Bank 1 Sensor 2 voltage for P0137 code diagnosis

Bank 1 Sensor 2 is located downstream — after the catalytic converter on the cylinder #1 side.

What Does P0137 Mean?

When your Check Engine Light turns on and a scan shows P0137, the PCM has detected that the downstream oxygen sensor on Bank 1 (Sensor 2) is producing unusually low voltage — specifically below 0.4V for 20+ consecutive seconds.

  • Bank 1: The engine side containing cylinder #1. On inline 4-cylinders, there's only one bank. On V6/V8 engines, consult your owner's manual.
  • Sensor 2 (Downstream): Located after the catalytic converter. Its role is to verify the converter is working correctly — not to regulate fuel mixture (that's Sensor 1's job).
  • Low Voltage: The PCM expects stable voltage around 0.4–0.6V. A persistent reading below 0.4V for 20 seconds triggers P0137.
Key difference: Sensor 1 oscillates rapidly (0.1V–0.9V) to regulate fuel trim. A healthy Sensor 2 holds a relatively steady mid-range voltage. If it's consistently low, that's the red flag.

Symptoms of P0137

P0137 may not cause obvious drivability issues immediately, but these signs commonly appear:

  • Check Engine Light (MIL) on — the primary indicator. The vehicle automatically fails an OBD-II emissions test with the light on.
  • Failed emissions inspection — the downstream sensor monitors catalytic converter efficiency; low voltage signals a compliance problem.
  • Reduced fuel economy — the PCM may run the engine rich when it cannot verify downstream conditions.
  • Rough or unstable idle — especially at traffic lights, due to incorrect fuel mixture adjustments.
  • Hesitation under load — sluggish acceleration or power loss when climbing hills or carrying weight.
Warning: Persistent incorrect fuel trim can accelerate catalytic converter degradation — turning a $150 sensor replacement into a $500–$1,500 converter repair. Don't delay.

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What Causes P0137?

Five primary causes, ordered by frequency — work through them in sequence before replacing any parts:

1

Faulty Downstream O2 Sensor — Most Common

Internal failure of the sensor's ceramic element or heater circuit. High-mileage sensors (100K+ miles) are especially prone. Accounts for ~60–70% of P0137 cases.

2

Wiring or Connector Damage

Corroded terminals, frayed wires, or a loose connector create resistance that reduces the voltage signal reaching the PCM. Common on vehicles exposed to road salt, heat, or vibration.

3

Exhaust Leak Upstream of Sensor 2

A leak draws in fresh air, diluting exhaust gases and causing artificially low voltage — even if the sensor itself is perfectly functional.

4

Failing Catalytic Converter

A degraded converter alters exhaust gas composition at Sensor 2, producing low or erratic voltage. Often paired with P0420 — if both appear, suspect the converter first.

5

PCM Issue — Rare

A PCM software glitch occasionally misreads sensor voltage. Only investigate after all hardware causes are definitively eliminated.

Quick Diagnosis Decision Path — What codes do you see?

You have P0137 — which other codes appear?
↓
Branch A: P0137 + P0420
→ Suspect Catalytic ConverterCheck if Sensor 2 oscillates like Sensor 1. Backpressure test recommended before buying a sensor.
Branch B: P0137 + P0141
→ Check Heater Circuit FirstP0141 = heater circuit fault. A cold sensor reads low. Fix the heater before condemning the sensor element.
Branch C: P0137 Only
→ Check Exhaust & Wiring FirstMonitor live voltage. Check for exhaust leaks upstream. Inspect connector corrosion before replacing the sensor.

How to Diagnose P0137 — Step by Step

Systematic diagnosis saves money. Follow these steps in order before purchasing any replacement parts:

1
Confirm the Code & Review Freeze-Frame Data

Connect your scanner to the OBD-II port. Confirm P0137 is active or pending, and record companion codes (P0136, P0420, P0141). Review freeze-frame data — it captures engine speed, load, coolant temp, and fuel trim at the exact moment the fault triggered.

2
Monitor Live Sensor Voltage

With the engine fully warmed up (10+ minutes), navigate to: Live Data → O2 Sensors → Bank 1 / Sensor 2 → Voltage. A healthy downstream sensor holds stable voltage between 0.4–0.6V. Below 0.4V consistently confirms the fault is active.

Pro tip: Also watch STFT and LTFT fuel trim values. Above +10% alongside P0137 suggests the PCM is compensating by running rich — a sign of exhaust dilution or sensor failure.
3
Inspect Wiring & Connectors

Locate the downstream sensor and inspect carefully for: green corrosion on terminals → clean with electrical contact cleaner; cracked insulation near heat sources → replace harness; loose connector pins → re-seat or crimp. A wiring fault can perfectly mimic a failed sensor.

4
Check for Exhaust Leaks

Inspect manifold gaskets, flex pipes, and converter inlet seams upstream of Sensor 2. A small exhaust leak drawing in fresh air produces identical low-voltage readings to a failed sensor. Listen for ticking or hissing on a cold start that fades as the exhaust warms up.

5
Test the Sensor with a Multimeter

Remove the cooled downstream sensor and test heater circuit resistance. Typical spec: 6–20 ohms between heater pins — verify against your vehicle's OEM service data. An open circuit or out-of-range reading confirms sensor failure.

6
Clear the Code & Verify the Repair

After repair, clear all codes. Complete a full OBD-II readiness drive cycle: cold start idle → city stop-and-go → 10+ min highway cruise → deceleration without braking. Re-scan after 50–100 miles. If P0137 does not return and all monitors show "Ready," the repair is confirmed.

Understanding Sensor Voltage — Live Data Guide

What different voltage readings from Bank 1 Sensor 2 mean during diagnosis:

Bank 1 Sensor 2 — Voltage Interpretation

Normal (Healthy Sensor)0.4V – 0.6V (steady)
0.4–0.6V
Borderline — Monitor Closely0.3V – 0.4V
0.3–0.4V
P0137 Trigger Zone — Fault ActiveBelow 0.4V for 20+ sec
< 0.4V
P0138 — High Voltage FaultAbove 0.9V consistently
> 0.9V (separate code)

* Verify against OEM service data for your specific vehicle.

If Sensor 2 oscillates like Sensor 1 (0.1V–0.9V): The catalytic converter has likely failed. This typically triggers both P0137 and P0420 simultaneously.

How to Fix P0137

Option 1: Replace the Downstream O2 Sensor (Most Common)

Allow exhaust to cool 30+ minutes. Apply penetrating oil to threads 10–15 min before removal. Use an O2 sensor socket (slotted for the wire). Torque to OEM spec (typically 27–44 Nm). Use an OEM-spec or quality aftermarket sensor matched to your exact make, model, and year.

Option 2: Repair or Replace Wiring / Connector

Clean corroded terminals with electrical contact cleaner and re-crimp. A $10–$30 fix that resolves many P0137 cases. Replace damaged harness sections as needed.

Option 3: Seal Exhaust Leaks

Small leaks can be sealed with high-temperature exhaust sealant ($10–$15). Cracked flex pipes or blown gaskets require component replacement. Always address exhaust leaks before replacing the O2 sensor.

Option 4: Replace the Catalytic Converter

Only when confirmed degraded via backpressure testing or live data. Replace with a compliant unit. Never attempt to bypass the converter — illegal and will set additional codes.

Option 5: PCM Reprogramming (Last Resort)

Only after all hardware causes are definitively eliminated. A PCM reflash at a dealer resolves software-related misreadings.

Repair Cost Breakdown

Repair DIY Cost Professional Cost Time
O2 Sensor Replacement — Most Common $50–$150 $150–$600 30–90 min
Wiring / Connector Repair $10–$30 $100–$300 30–60 min
Exhaust Leak Repair $5–$40 $100–$400 1–3 hrs
Catalytic Converter $150–$600 $500–$1,500 2–4 hrs
PCM Reprogram Not recommended $100–$400 1–2 hrs
Delay risk: Ignoring P0137 can turn a $50 sensor swap into a $1,500 catalytic converter replacement. Use live data to confirm the root cause first.

Diagnose P0137 Yourself with iCarsoft CR MAX BT

You need more than a basic code reader. The CR MAX BT gives you everything to confirm the root cause before spending on parts:

  • 7-inch HD touchscreen for clear live data monitoring
  • Real-time Bank 1 Sensor 2 voltage streaming
  • Bluetooth wireless — monitor during test drives
  • Freeze-frame capture for intermittent faults
  • STFT/LTFT fuel trim data for exhaust leak diagnosis
  • Code clearing + readiness monitor verification
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P0137 on Common Vehicle Makes

While P0137 can appear on any OBD-II gasoline vehicle, certain makes have known patterns:

Toyota / Lexus Very Common

  • Frequent on Camry, Corolla, RAV4 (150K+ miles)
  • Primary cause: ceramic element aging — not wiring
  • Use Denso or NGK OEM sensors — cheap aftermarket sensors cause re-triggers within weeks

Honda / Acura Very Common

  • Common on Accord, Civic, CR-V, Odyssey
  • Check connector behind heat shield first — the #1 corrosion point on Honda exhaust layouts
  • P0141 (heater circuit) often pairs with P0137

Ford / Chevrolet Common

  • Reported on F-150, Explorer, Fusion, Silverado, Malibu
  • Check exhaust manifold cracks and flex pipe for cracks
  • OEM or Bosch sensors recommended

Vauxhall / Opel Common

  • Frequent on Astra, Corsa, Insignia
  • In salt-road regions: connector seal integrity is the first check
  • Inspect for water ingress in the harness routing channel

VW / Audi Moderate

  • Appears on Golf, Jetta, Passat, A4, A6
  • Often paired with P0420 or P0422
  • Bosch sensors recommended

Other Makes Global

  • Common on BMW, Mercedes, Nissan, and Kia models as sensors degrade over 100K miles.

How to Prevent O2 Sensor Codes

  • Inspect the exhaust system every 6 months — check for rust, cracks, and heat damage, especially after winter road salt exposure.
  • Use the correct fuel and oil grade — low-quality fuel or incompatible oil can coat the O2 sensor's ceramic element with carbon deposits.
  • Scan proactively every 3–6 months — catch pending codes before they trigger the Check Engine Light and escalate repair costs.
  • Address P0137 promptly — a $100 repair can become a $1,000+ catalytic converter replacement through delay alone.
  • Consider proactive sensor replacement at 100K miles — replace all O2 sensors at 100,000–120,000 miles as preventive maintenance.

P0137 rarely appears in isolation. These codes often appear together and help pinpoint the root cause:

P0136
O2 Sensor Circuit — B1/S2 (general circuit fault)
P0138
O2 Sensor High Voltage — B1/S2 (>0.9V)
P0420
Catalyst Efficiency Below Threshold — often paired with P0137
P0157
O2 Sensor Low Voltage — Bank 2, Sensor 2
P0141
O2 Sensor Heater Circuit — B1/S2 (common on Honda)

Frequently Asked Questions About P0137

Can I drive with P0137? ▾
Yes, but only for short distances. Prolonged driving can damage the catalytic converter. Diagnose and fix within 1–2 weeks to avoid escalating repair costs.
Is P0137 serious? ▾
Yes, moderate-to-high severity. The car may drive normally at first, but the fault can cause catalytic converter damage and automatic emissions test failure if left unresolved.
Will replacing the O2 sensor always fix P0137? ▾
Not always. While a faulty sensor is the most common cause (~60–70%), exhaust leaks, wiring damage, and catalytic converter failure can all trigger P0137. Always diagnose with live data first.
How much does it cost to fix P0137? ▾
O2 sensor replacement costs $150–$600 professionally or $50–$150 DIY. Wiring repair runs $100–$300. Catalytic converter replacement costs $500–$1,500. Always diagnose before spending.
Can a bad catalytic converter cause P0137? ▾
Yes. A failing converter alters exhaust gas composition at Sensor 2, causing abnormally low voltage. This is especially likely if P0420 appears alongside P0137.
Can I pass emissions with P0137? ▾
No. P0137 triggers the Check Engine Light, causing automatic failure during an OBD-II emissions inspection. You must repair the fault, clear the code, and complete a full drive cycle before retesting.
Should I replace the O2 sensor or catalytic converter first? ▾
Always replace the O2 sensor first if testing shows it has failed — significantly cheaper ($50–$150) than a converter ($500+). Only replace the converter if live data and backpressure tests confirm it is defective.
What voltage should Bank 1 Sensor 2 read? ▾
A healthy downstream sensor holds stable voltage between 0.4V and 0.6V at operating temperature. P0137 triggers when voltage stays below 0.4V for 20+ consecutive seconds. Voltage consistently above 0.9V triggers P0138.
How do I find Bank 1 Sensor 2 in my car? ▾
Bank 1 is the cylinder bank containing cylinder #1. Sensor 2 is located after the catalytic converter on that bank — it typically has a longer wire harness than the upstream Sensor 1.
What cars most commonly get P0137? ▾
P0137 is especially frequent in Toyota (Camry, Corolla, RAV4), Honda (Accord, Civic, CR-V), Ford (F-150, Explorer, Fusion), Chevrolet (Silverado, Malibu, Equinox), and Vauxhall/Opel (Astra, Corsa).

Verified by iCarsoft Automotive Technicians

This guide is based on analysis of 10,000+ real-world OBD-II fault cases from Toyota, Honda, Ford, and GM vehicles. Our technicians review all diagnostic content to ensure accuracy and help car owners avoid unnecessary parts costs.

Wrap-Up

P0137 is a manageable fault when approached systematically. In most cases, the repair is a straightforward O2 sensor or wiring fix — inexpensive when caught early. The key is using live data to confirm the actual cause before replacing any parts.

  • Always confirm with live sensor voltage data — don't guess
  • Inspect wiring and check for exhaust leaks before buying a sensor
  • Clear the code after repair and complete a full drive cycle
  • Address P0137 within 1–2 weeks to protect the catalytic converter

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Disclaimer: This guide is for reference only. Always verify diagnostic procedures, torque specifications, and sensor compatibility against the OEM service manual for your specific vehicle. iCarsoft Technology Inc. is not responsible for any vehicle damage resulting from repairs performed without proper training or equipment.