P0137 — O2 Sensor Circuit Low Voltage

The diagnostic trouble code P0137 indicates a problem with the Oxygen Sensor (O2 Sensor) signal, specifically that the sensor is reading a low voltage signal. This situation suggests that the sensor may not be functioning properly or that there is an issue with the wiring or related components. It’s important to interpret this code carefully, as it can affect engine performance and emissions.

Note that the labels for this code can vary between vehicle manufacturers (OEMs), but the core meaning remains largely the same.

Manufacturer variations for trouble code P0137

The P0137 code may be identified differently by various vehicle manufacturers. These label variations often depend on the OEM’s specific coding systems but generally refer to similar issues related to the Oxygen Sensor Circuit Low Voltage.

• Ford: P0137 — « HO2S Circuit Low Voltage (Bank 1, Sensor 2) »
• GM: P0137 — « O2 Sensor 1/2 Circuit Low Voltage »
• Mercedes-Benz: P0137 — « O2 Sensor Signal Circuit Low »
• Volkswagen/ Audi /others: Similar labels indicating sensor circuit issues; specific labels vary depending on models.

What does trouble code P0137 mean?

This diagnostic trouble code P0137 means that the Engine Control Unit (ECU), which is the vehicle’s brain and manages various engine functions, has detected that the Oxygen Sensor (O2 Sensor) located after the catalytic converter (sensor 2, also called downstream sensor) is sending a voltage signal that is too low. This low voltage indicates that the sensor detects a lean mixture—more oxygen in the exhaust gases—or that the sensor isn’t responding correctly.

The ECU constantly monitors the O2 sensors to assess air/fuel mixture and ensure optimal engine operation and emissions control. When the sensor signal is persistently below expected levels, the ECU triggers code P0137.

This situation can be caused by a faulty sensor, wiring issues, or problems within the exhaust system, and usually appears during driving, especially during engine load changes or acceleration.

Severity and risks of trouble code P0137

While P0137 is generally considered a moderate issue, if left unaddressed, it can lead to several risks. These include increased emissions, reduced fuel efficiency, and potential damage to the catalytic converter. A poorly functioning or faulty sensor can also cause the engine to run with suboptimal air-fuel ratios, resulting in rough idling and hesitation.

Can the vehicle be driven with this code? Yes, in most cases, but with caution. It’s advisable to diagnose and repair the issue promptly to avoid long-term damage or increased emissions.

Symptoms of trouble code P0137

The symptoms associated with this code may not always be severe but can impact driving comfort and vehicle efficiency. Common symptoms include:

• Check Engine Light (CEL) illuminated on the dashboard
• Rough idling or irregular engine operation
• Reduced fuel economy
• Noticeable exhaust smell or increased emissions
• Possible hesitation or stalling during acceleration
• Possible failure of emissions tests

Most likely causes of trouble code P0137

The underlying causes of code P0137 are varied, but some are more common. Below are the most probable reasons, ranked from most to least likely:

1. Faulty downstream oxygen sensor (O2 sensor 2) — Usually the most common cause; sensor could be worn or damaged, giving false low readings.
2. Damaged or corroded wiring or connector — Wiring harnesses can degrade over time or suffer physical damage, causing signal disruptions.
3. Exhaust leaks upstream of the sensor — A leak can alter the oxygen readings and lead to false low voltage signals.
4. Exhaust system contamination or sensor contamination — Oil, dirt, or debris can impair sensor performance.
5. ECU software or calibration issues — Less common but possible, especially after software updates or modifications.

How to diagnose trouble code P0137

Diagnosing P0137 requires a systematic approach. Here are the generic steps to follow, suitable for most vehicles without manufacturer-specific tools:

1. Visual inspection — Check the wiring harness and connector to the O2 sensor for signs of damage, corrosion, or disconnection.
2. Examine the oxygen sensor — Look for physical damage, contamination, or deposits that might impair operation.
3. Test the wiring continuity — Use a multimeter to verify that the wiring circuit is intact between sensor and ECU.
4. Check for exhaust leaks — Inspect the exhaust system for leaks upstream of the sensor, which can alter readings.
5. Read live data — Use a scan tool to monitor the sensor voltage during engine operation to assess responsiveness and range.
6. Compare sensor readings — Check the downstream sensor readings relative to upstream sensors, if available, for anomalies.
7. Inspect related components — Verify that the catalytic converter and exhaust system are functioning properly and not blocked or damaged.

Possible repairs for trouble code P0137

Addressing P0137 typically involves replacing or repairing faulty components, but some fixes are more straightforward than others. Here are common repairs linked to the root causes:

• Replace the faulty downstream oxygen sensor — Usually a semi-professional task but best done by a qualified technician for accuracy.
• Repair or replace damaged wiring or connectors — Basic electrical repair; requires some skill in handling wiring harnesses.
• Seal exhaust leaks — Requires some mechanical work to locate and fix leaks, usually a job for a professional.
• Clean or replace contaminated sensors — Sometimes sensors can be cleaned if contamination is limited; otherwise, replacement is recommended.
• Update ECU software or reset calibration — Performed by professionals with manufacturer-specific diagnostic tools.

Vehicles commonly associated with trouble code P0137 in Europe

In European markets, this code is often linked to vehicles with a range of common makes and models. While exact prevalence data varies, certain brands are more affected:

Volkswagen Group: Volkswagen, Audi, SEAT, Škoda — typical for many petrol and diesel models.

Ford: Various models, especially marginally-aged vehicles with oxygen sensor-related issues.

Mercedes-Benz: Some models with exhaust and emissions management systems prone to O2 sensor problems.

It’s important to perform a vehicle-specific diagnosis rather than relying solely on brand or model assumptions.

Frequent mistakes with trouble code P0137

The diagnosis and repair process for P0137 can sometimes be marred by common pitfalls. These include:

• Replacing the sensor without diagnosing wiring issues — Leads to the same problem recurring if wiring damage remains unaddressed.
• Ignoring exhaust system leaks — Leaks upstream of the sensor can falsely trigger low voltage readings, leading to unnecessary sensor replacements.
• Overlooking connector and wiring corrosion — Dirty or corroded contacts often cause signal issues that mimic sensor faults.
• Failing to clear the code after repair — Failure to clear the fault memory can make it seem as if the repair didn’t work, delaying further diagnosis.

FAQ — trouble code P0137

Can this code disappear on its own? — Usually not. Once the ECU detects a persistent low voltage signal from the downstream O2 sensor, the code will remain until the root cause is addressed. However, in some cases, a temporary glitch can clear itself if wiring issues or sensor faults resolve themselves, but this is uncommon.

Can I keep driving? — Yes, for a limited period, but it is not recommended. Continuing to drive with this fault can lead to increased emissions, potential damage to the catalytic converter, and decreased engine efficiency. It’s best to diagnose and repair as soon as possible.

Why does the code return after clearing? — If the underlying issue, such as wiring damage, exhaust leaks, or a faulty sensor, is not fixed, the code will reappear after clearing. Persistent low voltage readings will continually trigger the fault detection.