P0137

What it means

P0137 means the engine control unit has seen a persistently low signal voltage from the downstream oxygen sensor (Bank 1, Sensor 2), which sits after the catalytic converter. The signal stayed below the expected range, often close to zero volts, when it should be switching or sitting at a steady mid-to-high value during warm running. The cause may be the sensor, its wiring or a real exhaust or fuelling condition, so it needs proper testing.

Symptoms

• Engine management light on
• Usually no noticeable change in driveability
• Possible slightly poor fuel economy if fuelling is also affected
• Failed emissions test or readiness monitors not completing
• Other fuel trim or catalyst codes stored alongside

Possible causes

• Failed or aged downstream oxygen sensor (Bank 1, Sensor 2)likely
• Damaged, chafed or corroded sensor wiring or connector, including a short to earth or an open circuitlikely
• Exhaust leak near the sensor letting in air and giving a false lean readingpossible
• Sensor heater circuit fault, such as a blown fuse or failed heater element, depending on the modelpossible
• Contamination of the sensor by coolant, oil or silicone, from an engine fault or unsuitable sealantspossible
• Persistent lean running condition or a fault in the engine control unitrare

How to diagnose

1. Read all stored and pending codes and note the freeze frame data (engine temperature, load, fuel trims) to see the conditions when the fault set
2. Check for other related codes, especially fuel trim, misfire, heater circuit or upstream sensor faults, and deal with those first
3. Inspect the sensor wiring and connector for heat damage, chafing, water ingress, corrosion and bent or pushed-back pins
4. Check for exhaust leaks between the engine and the sensor, including the manifold, flexible joint and catalytic converter joints
5. Using live data, watch the Bank 1 Sensor 2 voltage at operating temperature and compare it with the upstream sensor; it should be steadier than the upstream signal but not stuck near zero
6. Check the sensor heater fuse, supply and earth, and measure heater resistance against the manufacturer's specification for that model
7. Check the sensor signal and earth wiring for continuity and for shorts to earth using the wiring diagram for the vehicle
8. Check for signs of coolant or oil contamination, and review fuel trims for a lean condition

How to fix

• Replace the downstream oxygen sensor if live data and electrical tests show it is faulty or contaminated
• Repair or replace damaged wiring, connectors or terminals, and renew any blown heater fuse after finding why it failed
• Repair exhaust leaks upstream of the sensor, using the correct gaskets and fixings
• Correct any underlying engine fault causing contamination or a lean condition, such as a coolant leak, oil consumption or air leak
• Clear the code after repair and complete a drive cycle to confirm the monitor runs and passes

Can I keep driving?

Nearby codes

• P0136GenericO2 Sensor Circuit Bank 1 Sensor 2
• P0138GenericO2 Sensor Circuit High Voltage Bank 1 Sensor 2