How much does it cost to fix P0137?

DIY repair typically costs $25–$100 for parts. Professional repair runs $200–$520 including parts and labor.

P0137

Powertrain

Low

O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)

Get Your FREE AI Diagnostic Report

Enter your vehicle for a personalized diagnosis for code P0137

The P0137 code means the downstream oxygen sensor on Bank 1 is reporting a voltage consistently below 0.21 volts for longer than 2 minutes. The downstream sensor normally shows a relatively steady voltage (compared to the rapidly switching upstream sensor) because the catalytic converter smooths out the exhaust gas composition. When this sensor is stuck low, it could mean the sensor has failed or there's an actual lean exhaust condition.

Since the downstream sensor (Sensor 2) is primarily used for catalytic converter monitoring rather than fuel control, this code typically doesn't cause noticeable drivability symptoms. You may see a slight drop in fuel economy if the ECM uses the downstream sensor for minor fuel trim adjustments, but in most vehicles, the engine will run normally. The main concern is emissions compliance — this code will cause an emissions test failure.

The most common fix is replacing the downstream O2 sensor. Before doing so, check for exhaust leaks around the catalytic converter flanges and downstream piping, as this is a common and free fix if a gasket or clamp just needs tightening. Also check whether you have any upstream sensor codes (P0130–P0135) or lean condition codes (P0171, P0174) — if so, fix those first, as they may be causing the downstream sensor to correctly report a lean condition. The downstream sensor is located under the vehicle and may require penetrating oil to remove if it's been in place for many years.

Severity

Low — MonitorThis Month

Symptoms

•Check Engine Light illuminated
•Slight reduction in fuel economy
•Failed emissions test
•No significant change in engine performance or drivability
•Possible slight rough idle in some vehicles

Likely Causes

Failed downstream O2 sensor stuck at low voltage35%

The downstream sensor's output has degraded to remain below the 0.21V threshold for more than 2 minutes, indicating internal failure of the sensor element.

Exhaust leak near downstream sensor25%

An exhaust leak between the catalytic converter and the downstream sensor allows ambient air in, diluting the exhaust sample and causing a persistent low voltage (lean) reading.

Lazy or failing upstream O2 sensor causing actual lean condition20%

If the upstream sensor is slow to respond, the fuel mixture can swing lean. The downstream sensor correctly reports low voltage because the exhaust actually is lean after passing through the converter.

O2 sensor signal wire shorted to ground20%

Physical damage to the downstream sensor wiring — from road debris or undercarriage contact — can short the signal wire to ground, pulling voltage to near zero.