P0137 Rear O2 Sensor Low Voltage (Bank 1)
Drive normally - check soon
The rear oxygen sensor on bank 1, after the catalytic converter, is stuck reading low. A failing sensor, a wiring fault or an exhaust leak near it is the usual cause. Safe to drive, but it fails emissions tests.
- Safe to drive?
- Yes
- Typical cost at a shop
- $417-$596 RepairPal national averages, parts and labor
- Emissions test
- Yes, while the check engine light is on, most OBD emissions tests fail the car.
Watch both oxygen sensors and the fuel trims live to tell a bad sensor from a leak.
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What it means
The rear oxygen sensor on bank 1 sits after the catalytic converter and tells the computer how well the converter works. P0137 means its signal stays too low, as if the exhaust there were very lean. The sensor or its wiring may have failed, or outside air may be leaking into the exhaust near it.
The technical version
A narrow-band rear sensor normally gives a steady signal in the middle-to-high part of its 0.1 to 0.9 V range on a warm engine with a working converter. P0137 sets when the signal stays below its limit, often during a test where the computer richens the mixture and expects the rear sensor to rise. An exhaust leak upstream of the sensor pulls in air and makes it read low.
Official name: O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2).
Symptoms
- Usually only the check engine light.
- Sometimes an exhaust leak noise.
Causes, most likely first
| Cause | How likely | How to tell |
|---|---|---|
| An old or failed rear oxygen sensor | most common | The sensor is original on a high-mileage car and reads flat low. |
| An exhaust leak before the rear sensor | common | Ticking or puffing noise; soot at a joint or gasket. |
| Wiring chafed or shorted to ground, or a corroded connector | common | Damaged insulation near the exhaust. |
| A real lean condition | less common | Lean fuel trims and P0171 with it. |
How likely is our ranking from repair data and common practice, not a published rate.
What the live data shows
On a warm engine with a working converter, the bank 1 rear sensor usually sits fairly steady, often around 0.5 to 0.7 V. With P0137 it stays low, under about 0.2 V, even when you snap the throttle (which should push it up). Check fuel trims too: if long-term trim is high and positive, the engine may really be lean.
What to check first, in order
-
Look and listen for exhaust leaks ahead of the rear sensor.
Outside air makes it read low.
What the data shows: No reading needed.
Cost: free to look
-
Inspect the sensor wiring and connector.
Heat damage is common.
What the data shows: No reading needed.
Cost: free to look
-
Watch the rear sensor and fuel trims on a warm engine.
It shows a dead sensor or a lean engine.
What the data shows: A rear sensor that never rises above about 0.2 V points to the sensor or a leak.
Cost: no cost if you have a scanner
-
Fix an exhaust leak if you find one.
A leaking manifold gasket is a common spot.
What the data shows: The rear sensor reads normally again.
Cost: $417-$596 at a shop (Exhaust manifold gasket replacement, RepairPal)
-
Replace the rear oxygen sensor.
If wiring and leaks check out.
What the data shows: The sensor reads normally again.
Cost: $440-$523 at a shop (Oxygen sensor replacement, RepairPal)
Is it safe to drive?
Drive normally - check soon
Yes. The rear sensor mostly checks the converter; it does little to steer fueling.
Usually safe to drive. The car runs the same in most cases, but the computer cannot judge the catalytic converter, and you will fail an emissions test until it is fixed. If lean codes come with it, look at those first.
Stop driving and get help if
- The check engine light flashes.
- You hear a loud exhaust leak or smell exhaust inside the car.
What it costs
| Repair | Typical cost |
|---|---|
| Exhaust manifold gasket replacementRepairPal, updated September 3, 2026 | $417-$596 |
| Oxygen sensor replacementRepairPal, updated September 3, 2026 | $440-$523 |
National averages for the full job at a shop, parts and labor, from RepairPal (updated September 3, 2026). Your price depends on the car and the area. Many of the first checks on this page cost nothing with a scanner. Oxygen sensor replacement was CarMD's number 2 check engine repair in 2025, at an average of $287. CarMD averages come from a different method (repairs reported by its users), so they can sit below RepairPal's shop estimates.
Sources for the notes: CarMD 2026 Vehicle Health Index (press release, April 22, 2026).
Can I clear it? Will it come back?
After the repair, clear the code and drive. The oxygen sensor and catalyst monitors should complete within a few drives.
Will it fail an emissions test?
Yes, while the check engine light is on, most OBD emissions tests fail the car.
Related codes
Also related, no guide yet: P0136, P0157.
How Obie handles P0137
Obie reads the rear sensor, the front sensor and the fuel trims together and tells you whether to suspect the sensor, a leak or a lean engine. Obie is part of ScanMyCar Pro. Codes and live sensors are free.
Questions people ask
Is P0137 the upstream or downstream sensor?
Downstream: the rear sensor on bank 1, after the catalytic converter.
Can I drive with P0137?
Usually yes. Fix it before an emissions test.
Does P0137 mean my catalytic converter is bad?
No. It points to the sensor, its wiring or an exhaust leak. A bad converter sets P0420.
Sources
- RepairPal: P0137 code page repairpal.com
- RepairPal: Exhaust manifold gasket replacement (updated September 3, 2026) repairpal.com
- RepairPal: Oxygen sensor replacement (updated September 3, 2026) repairpal.com
- CarMD 2026 Vehicle Health Index (press release, April 22, 2026) prnewswire.com
- Texas DPS emissions testing FAQ dps.texas.gov
- Arizona myazcar.com: OBD and the check engine light myazcar.com
A guide, not a diagnosis. This page describes what P0137 generally means across OBD2 cars. What is actually wrong with your car depends on its live data and its history, and any repair decision deserves a proper diagnosis, whether that is you with a scanner or a professional with a lift.