📟
P0137 points to the O2 sensor BEHIND the catalytic converter on bank 1. Bank 1 is the side of the engine with cylinder #1 (check your service manual). A stuck-low downstream sensor is usually a dead sensor or an exhaust leak letting fresh air in upstream. See O2 sensor sockets on Amazon ↗
These are statistical causes across ALL vehicles - your exact car may rank differently
For example, on a Honda 4-cyl the downstream O2 sensor causes P0137 64% of the time, but on a GM 5.3L V8 the catalytic converter is the cause 71% of the time. Get a probability ranking built specifically for your year, make, model, and mileage.
🔎 Get the ranking for my exact car - $5.99 →
🎯 Top Causes & Probability
50%
#1 - Most Likely
Failed Downstream O2 Sensor (Bank 1, Sensor 2)
O2 sensors are wear items that degrade over 80k–120k miles. The downstream sensor on bank 1 has lost its ability to switch correctly and is stuck at low voltage. Replacement is the standard fix and resolves P0137 in roughly half of cases.
🔩 Part
$30–$180
👨🔧 Labor
$40–$120
⚡ DIY Difficulty
Easy
25%
#2 - Check First
Exhaust Leak Upstream of the Sensor
A crack in the exhaust manifold, broken stud, or leaking flange between the catalytic converter and the bank 1 downstream sensor pulls fresh air into the exhaust stream, making the sensor read lean (low voltage). Listen for ticking on a cold start - the classic exhaust leak symptom.
🔩 Part
$20–$300
👨🔧 Labor
$100–$400
⚡ DIY Difficulty
Medium
15%
#3 - Less Common
Genuine Lean Condition
A real lean fueling condition (vacuum leak, low fuel pressure, dirty MAF) makes the downstream sensor read lean. P0137 alongside P0171 strongly suggests a true lean condition rather than a sensor or exhaust problem - fix the lean cause first.
🔩 Part
$15–$300
👨🔧 Labor
$50–$300
⚡ DIY Difficulty
Medium
10%
#4
Wiring / Connector Damage
O2 sensor harnesses run close to hot exhaust and often melt or chafe over time. A signal wire grounded by a melted insulation pulls voltage low. Inspect the harness for damage and check connector pins for corrosion before replacing the sensor.
🔩 Part
$5–$60
👨🔧 Labor
$50–$150
⚡ DIY Difficulty
Medium
🚗 Most Affected Vehicles
🔧 Step-by-Step Diagnosis
- Check for an Exhaust Leak Upstream of B1S2 - With the engine cold, listen near the exhaust manifold and converter on bank 1 for ticking. A propane test or smoke test confirms small leaks. Fix any leak before replacing the sensor.
- Read Live O2 Voltage Data - Watch bank 1 sensor 2 voltage with a scan tool at idle. A healthy downstream sensor sits relatively steady around 0.6–0.8V. Stuck below 0.2V with no exhaust leak confirms a failed sensor.
📍 Find a Trusted Shop Near You
Please enter a valid 5-digit ZIP code.
Tips for Choosing a Shop
- Ask if they charge a diagnostic fee and whether it applies toward the repair
- Request a written estimate before approving any work
- Ask specifically about the part brand - OEM vs. aftermarket matters for this code
- Check Google reviews for recent mentions of the specific repair you need