P0137 trouble code: What it means and how to fix it

Learn what a P0137 trouble code means and how to fix it

A P0137 trouble code is defined as: Oxygen Sensor Circuit Low Voltage (Bank 1 Sensor 1). This sensor is located on the engine bank that houses #1 cylinder and is located AFTER the catalytic converter. The oxygen sensor measures oxygen levels in exhaust gases post-combustion to optimize engine performance and minimize air pollution. If oxygen levels are too low, indicating a rich fuel mixture, the PCM reduces fuel delivery. Conversely, if oxygen levels are too high, indicating a lean mixture, the PCM increases fuel delivery.

The PCM sends a reference voltage (usually 5-volts) to the variable resistor in the oxygen sensor and looks for a return voltage. Once the sensor is heated up, the PCM expects to see a varying voltage. If the PCM sees a constant low voltage, it will set a trouble code P0137.

The most common causes of a P0137 trouble code

The most common causes are a vacuum leak that allows too much unmetered air into the combustion chamber, low fuel pressure or clogged fuel injectors, a bad oxygen sensor, or a poor connection either at the PCM or O2 sensor.

TEST: It is very difficult to test an oxygen sensor without either a scope or scan tool. The most effective way to determine if you have a vacuum leak is to examine the fuel trim reading on a scan tool. If you have a vacuum leak and the sensor detects a continuous lean exhaust condition, the PCM will add fuel to compensate. Fuel trim should be as low as possible but never approaching 25%. That would indicate a vacuum leak.

To learn how to replace an oxygen sensor, click here

© 2012 Rick Muscoplat