Powertrain Fuel & Air medium

P0137 Code — O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2) (Causes & How to Fix)

Fix OBD-II code P0137: O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2). Step-by-step diagnosis and repair guide.

⏱️ Time30-60 minutes
📋 Severitymedium
🚗 Applies ToToyota, Honda, Ford, Chevrolet, Jeep
⚠️ DTC CodeP0137
P0137 — Powertrain Fuel & Air diagnostic guide

What Does DTC P0137 Mean?

P0137 on your Powertrain Fuel & Air system means: The ECM sees a voltage that’s too low from the downstream oxygen sensor on bank 1. This usually means the sensor isn’t reporting enough oxygen, suggesting a lean condition or a wiring problem.

How to Diagnose and Fix P0137 — Step by Step

  1. 1

    Visual Inspection – Connectors, Wiring, and Gas Cap

    1. Turn off the engine and let it cool for at least 15 minutes. 2. Disconnect the negative battery terminal (use a 10 mm socket). 3. Locate the downstream O₂ sensor (Bank 1, Sensor 2) – it’s usually just before the catalytic converter. 4. Pull the sensor plug and look for bent pins, corrosion, or loose clamps. 5. Follow the wiring harness back toward the PCM and check for chafed or cracked insulation. 6. While you’re at it, verify the fuel‑cap is seated properly; a loose cap can cause lean‑related codes.

  2. 2

    Read Live Data – O₂ Voltage and Fuel Trim

    1. Re‑connect the battery and start the engine. 2. Plug an OBD‑II scanner into the DLC and select “Live Data.” 3. Watch the Bank 1‑Sensor 2 voltage (PID 0x34). At idle it should fluctuate between ~0.1 V and ~0.9 V. 4. Note the short‑term fuel trim (STFT). A very high positive STFT (> 15 %) often accompanies a low‑voltage sensor. 5. Record the values for later comparison.

  3. 3

    Voltage Test – Sensor Signal with Multimeter

    1. With the engine at operating temperature, back‑probe the sensor signal wire while the engine is running. 2. Set the digital multimeter to DC volts. 3. A healthy downstream sensor will show a rapidly changing voltage between 0.1 V and 0.9 V as the engine cycles. 4. If the reading stays below ~0.1 V or is a steady voltage, the sensor is likely defective or the circuit is open. 5. Compare the reading to the live data you captured earlier.

  4. 4

    Heater Circuit Check – Resistance Test

    1. Turn off the engine and disconnect the sensor plug. 2. Measure resistance between the heater positive and negative terminals (usually two middle pins). 3. Most O₂ sensor heaters read between 2 Ω and 5 Ω. 4. An open circuit (∞ Ω) or a resistance far outside this range indicates a failed heater, which can cause low‑voltage readings during warm‑up. 5. Replace the sensor if the heater is out of spec.

  5. 5

    Exhaust Leak Inspection – Before the Sensor

    1. With the engine cool, inspect the exhaust pipe and gasket that sit upstream of the downstream sensor. 2. Look for soot, cracks, or loose clamps. 3. A leak before the sensor lets extra oxygen into the exhaust, forcing the sensor voltage low. 4. Tighten or replace the leaking section, then clear the code and retest. 5. If no leak is found, move to the next step.

  6. 6

    Replace the Downstream O₂ Sensor

    1. Raise the vehicle and support it on jack stands. 2. Remove the sensor with an O₂ sensor socket (usually 22 mm). 3. Apply anti‑seize compound to the new sensor threads (avoid the tip). 4. Install the new sensor, torque to the manufacturer’s spec (often 30–45 Nm). 5. Reconnect the wiring harness, lower the car, and clear the code. 6. Drive the vehicle for a few minutes, then re‑scan to confirm the P0137 is gone.

When to Call a Professional Mechanic

If the sensor voltage stays low after checking wiring, or if you discover an exhaust leak you cannot safely repair yourself, have a qualified technician perform a thorough PCM and fuel‑system inspection.

Diagnostic Flowchart

Follow this visual guide to systematically diagnose P0137:

Quick 60‑Second Check

Your check engine light just came on and the scanner shows P0137. Before you look at a full diagnosis, do this fast visual sweep:

  1. Is the fuel cap tightened?
  2. Does the sensor plug look loose or corroded?
  3. Is there any obvious damage to the wiring harness near the sensor?

If any of the above are true, fix it, clear the code, and see if it returns. Often a simple connector issue resolves the problem in under five minutes.

What You’ll Notice While Driving

Drivers with a P0137 code commonly report:

  • Rough idle – the engine may shake or stall at stoplights.
  • Hesitation on acceleration – a momentary stumble when you press the gas.
  • Poor fuel economy – the computer leans out the mixture trying to compensate for a perceived lean condition.
  • Engine stalling – especially when the engine is cold or under load.

These symptoms are tied to the downstream O₂ sensor’s job: monitoring exhaust after the catalytic converter and telling the PCM whether the converter is working efficiently. When the sensor reports an abnormally low voltage, the PCM thinks the exhaust is too lean and adjusts fuel delivery, which you feel as the above drivability issues.

Why This Happens (Root Causes)

Faulty Downstream O₂ Sensor

The most direct cause is a sensor that can no longer generate a usable voltage signal. Age, contamination from oil or coolant, and heater‑element failure are typical culprits.

Wiring or Connector Problems

A broken wire, a short to ground, or a corroded connector will pull the sensor voltage down. Heat‑induced cracking is common on vehicles that run hot exhausts, such as Ford trucks and Chevy midsize SUVs.

Exhaust Leak Before the Sensor

A leak upstream of the downstream sensor lets extra fresh air mix with exhaust gases, making the sensor see a lean mixture and output low voltage. This is a frequent issue on Jeep Wrangler models with cracked exhaust manifolds.

PCM or Ground Issues

Rarely, the powertrain control module’s input circuit can develop a high resistance ground, causing low voltage readings even when the sensor is healthy. This usually requires a professional scan tool to confirm.

Step‑by‑Step Diagnosis & Repair

Below is a logical progression from the easiest checks to the most involved repairs. Follow each step exactly as written; the “good vs. bad” notes will tell you when to move on.

1. Visual Inspection – Connectors, Wiring, and Gas Cap

Good: Plug is seated, pins are clean, wiring is intact, fuel cap clicks firmly. Bad: Bent pins, cracked insulation, loose connector, or a gas cap that wobbles.

Tools: 10 mm socket, ratchet, flashlight.

If you find a loose plug or damaged wire, repair or replace the harness section and clear the code. Re‑scan; if the code disappears, you’re done.

2. Live Data Review – O₂ Voltage & Fuel Trim

Good: Voltage swings between 0.1 V and 0.9 V; short‑term fuel trim stays within ±10 %. Bad: Voltage stuck near 0 V or 0.1 V, and fuel trim consistently high (+15 % or more).

Tools: OBD‑II scanner with live‑data capability.

Record the idle voltage and note any steady‑state values. If the sensor never rises above 0.2 V, the sensor itself is suspect.

3. Voltage Test – Sensor Signal with Multimeter

Good: Rapidly changing voltage (0.1‑0.9 V) as the engine cycles. Bad: Flat reading below 0.1 V or a constant voltage that never moves.

Tools: Digital multimeter, back‑probe clip.

Place the probe on the signal wire while the engine runs at idle. If the reading is flat, move to step 4.

4. Heater Circuit Check – Resistance Test

Good: Heater resistance between 2 Ω and 5 Ω. Bad: Open circuit (∞ Ω) or resistance far outside the 2‑5 Ω window.

Tools: Digital multimeter.

A failed heater often shows low voltage only during warm‑up; after the engine reaches operating temperature the voltage may appear normal, which can confuse the PCM.

5. Exhaust Leak Inspection – Upstream of Sensor

Good: No cracks, tight clamps, no soot escaping from joints. Bad: Visible cracks, loose bolts, soot blowing out of a joint.

Tools: Jack, jack stands, exhaust inspection mirror.

Repair any leak you find (gasket replacement, clamp tightening). A leak can masquerade as a sensor problem, so always verify this before swapping parts.

6. Replace the Downstream O₂ Sensor

Good: New sensor produces a healthy voltage swing; code clears after a short drive. Bad: Code returns immediately, indicating a deeper wiring or PCM issue.

Tools: O₂ sensor socket, torque wrench, anti‑seize compound.

Install the sensor per the vehicle’s service manual (typically 30–45 Nm). After installation, clear the code and drive for at least five minutes. Re‑scan; the P0137 should be gone.

Cost Breakdown

| Repair Option | Parts (USD) | Labor (USD) | Total (USD) | |

Real-World Diagnostic Scenario: P0137

When a technician encounters P0137 in the shop, the diagnostic approach differs significantly from other codes. Unlike generic fuel system codes, P0137 requires checking specific subsystems in a particular order to avoid misdiagnosis. Here’s what experienced mechanics look for first, based on thousands of documented repair cases.

Several manufacturers have issued TSBs specifically addressing the root causes of P0137. Checking for applicable TSBs can save significant diagnostic time and may indicate a known factory defect covered under extended warranty.

Note: TSB availability varies by manufacturer and model year. Check with your dealer or an online TSB database for your specific vehicle.

What Does Code P0137 Mean?

Code P0137 refers to a problem with the downstream oxygen sensor on bank 1 of your vehicle’s engine. The oxygen sensor, also known as the O2 sensor, measures the amount of oxygen in the exhaust gases and sends this information to the Engine Control Module (ECM). The ECM uses this data to adjust the air-fuel mixture in the engine. When the ECM detects a voltage that’s too low from the downstream oxygen sensor on bank 1, it sets code P0137. This usually means the sensor isn’t reporting enough oxygen, suggesting a lean condition or a wiring problem.

A lean condition occurs when there’s more air than fuel in the engine’s combustion mixture. This can cause the engine to run hotter than normal and may lead to decreased performance and fuel efficiency. Common symptoms of code P0137 include a check engine light, decreased fuel efficiency, and a slight decrease in engine performance. In some cases, you may notice a slight hesitation or rough idling.

The downstream oxygen sensor on bank 1 is usually located after the catalytic converter. Its purpose is to monitor the effectiveness of the catalytic converter in reducing emissions. If you’re experiencing code P0137, it’s essential to diagnose and repair the issue promptly to prevent potential damage to your vehicle’s engine and emissions system.

Common Causes of P0137

Here are the common causes of code P0137, ordered by likelihood:

  • Faulty downstream oxygen sensor on bank 1 (40-50% of cases)
  • Wiring issues or corrosion in the oxygen sensor circuit (20-30% of cases)
  • Lean air-fuel mixture due to a vacuum leak or faulty fuel injector (15-25% of cases)
  • Faulty catalytic converter (5-15% of cases)
  • Oxygen sensor contamination or damage (5-10% of cases)
  • ECM software issues or calibration problems (less than 5% of cases)

Can I Still Drive with Code P0137?

Code P0137 has a medium severity level, which means you can still drive your vehicle, but it’s not recommended to ignore the issue. A lean air-fuel mixture can cause the engine to run hotter, potentially leading to costly repairs down the road. Additionally, a faulty oxygen sensor can cause your vehicle to fail emissions tests. It’s best to diagnose and repair the issue as soon as possible to prevent potential damage and ensure your vehicle runs efficiently.

Estimated Repair Costs

Here are the estimated repair costs for the top 4 causes of code P0137:

CauseDIY CostShop Cost
Faulty downstream oxygen sensor on bank 1$50-$200$200-$500
Wiring issues or corrosion in the oxygen sensor circuit$20-$100$100-$300
Lean air-fuel mixture due to a vacuum leak or faulty fuel injector$50-$500$200-$1,000
Faulty catalytic converter$300-$1,500$500-$2,500

Frequently Asked Questions

Q: I’ve got a Toyota Camry with code P0137. Can I replace the oxygen sensor myself? A: Yes, replacing the oxygen sensor is a relatively straightforward process that you can do yourself with basic tools. However, make sure to consult your repair manual or a reliable source for specific instructions.

Q: I have a Honda Civic with code P0137. Will a new oxygen sensor fix the problem? A: Not always. While a faulty oxygen sensor is a common cause of code P0137, it’s essential to diagnose the issue thoroughly to rule out other potential causes, such as wiring issues or a lean air-fuel mixture.

Q: I’ve noticed a decrease in fuel efficiency with code P0137 on my Ford F-150. Will fixing the issue improve my gas mileage? A: Yes, fixing the issue causing code P0137 can improve your fuel efficiency. A lean air-fuel mixture can cause your engine to consume more fuel than necessary, so correcting the issue can help restore your vehicle’s optimal fuel efficiency.

Q: Can code P0137 cause damage to my Chevrolet Silverado’s engine? A: If left unchecked, code P0137 can potentially cause damage to your engine. A lean air-fuel mixture can cause the engine to run hotter, leading to costly repairs. It’s essential to diagnose and repair the issue promptly.

Q: I’ve got a Jeep Wrangler with code P0137. Can I still drive it off-road? A: While code P0137 has a medium severity level, it’s not recommended to drive your vehicle under extreme conditions, such as off-roading, without addressing the issue. A faulty oxygen sensor or lean air-fuel mixture can cause your engine to overheat or perform poorly under stress.

Related Powertrain Fuel & Air DTC Codes

P0136 P0138 P0140

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Published: · Updated: · By FixCarCodes Team

This guide is for informational purposes only. Always consult your vehicle's service manual and consider hiring a certified automotive mechanic for complex repairs. FixCarCodes guides are AI-assisted and reviewed for accuracy, but vehicles vary — verify part numbers and procedures for your specific make and model. Learn about our editorial process.