What's the difference between P0136 and P0137?

They cover the same part — the downstream O2 sensor on bank 1 — but P0136 is the broader 'circuit' code that a range of downstream faults can trigger, while P0137 specifically means the signal is stuck low (near 0V). If you have both, treat them as describing one problem on one sensor. The low-voltage detail in P0137 points you toward a short to ground, an open circuit, or an exhaust leak letting in air.

Can an exhaust leak cause P0137?

Yes, and it's commonly missed. A leak ahead of the downstream sensor — a cracked downpipe, a bad flange gasket, or a pinhole in the catalyst housing — lets atmospheric air reach the sensor. All that extra oxygen makes the sensor read lean, which shows up as a low voltage. Before buying a sensor, listen for a tick or hiss near the exhaust on a cold start and inspect the joints ahead of the sensor.

Is P0137 safe to drive with?

Usually, yes. The downstream sensor monitors catalyst efficiency rather than controlling fuel, so the car typically drives normally. You'll lose a little fuel economy and you won't pass emissions until it's fixed. If the cause is an exhaust leak, that can grow over time and get noisier, so it's worth addressing within a few weeks rather than ignoring.

How much does it cost to fix P0137?

A downstream O2 sensor is $150-400 installed. Wiring repair runs $50-500 depending on the damage. An exhaust leak repair depends entirely on the location and severity. The cheapest first move is a careful wiring and exhaust inspection — many P0137 codes are solved without replacing the sensor at all.

OBD-II trouble code

P0137: O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)

The downstream oxygen sensor on bank 1 is reporting a voltage that's stuck low — sitting near zero and refusing to rise. The usual culprits are a signal wire shorted to ground, an open circuit, an exhaust leak pulling in fresh air, or a worn-out sensor.

Quick facts

System: Powertrain
Category: Oxygen Sensor
Severity: Medium severity
Drivable: Usually safe to drive short-term
Repair cost range: $150 – $600
DIY difficulty: Intermediate DIY

What does P0137 mean?

P0137 is the low-voltage member of the downstream-sensor family on bank 1. It's closely related to P0136 (the general circuit code for the same sensor) and is the mirror image of P0138 (stuck high). Where P0136 can be set by a range of downstream faults, P0137 specifically means the PCM is watching the sensor signal sit pinned near 0V — a flat, low reading that a working post-catalyst sensor should never produce.

The downstream oxygen sensor lives behind the catalytic converter. Its purpose is to confirm the catalyst is doing its job, not to control fuel delivery, so on a healthy car its voltage should rest fairly steady around 0.4V to 0.7V. A reading stuck at the bottom of the scale tells the PCM one of a few things, and the failure modes for a low signal are distinct from the high-signal causes that set P0138.

The leading cause is an electrical fault that pulls the signal down: a signal wire chafed against the chassis or exhaust and shorted to ground, an open circuit from a broken wire or backed-out connector pin, or a corroded connector. The second common cause is an exhaust leak ahead of the sensor — a cracked downpipe, a leaking flange, or a pinhole in the catalyst housing lets atmospheric air reach the sensor, and all that extra oxygen makes the sensor read lean (low voltage) even though the engine isn't actually lean. The third is simple sensor wear; an aged element loses its ability to generate voltage and drifts low. A useful field test is to unplug the sensor and watch the PCM's reading — if the value behaves differently disconnected versus connected, you've learned whether the fault is in the sensor or the harness.

Common causes

Signal wire shorted to ground — chafed insulation contacting the chassis or exhaust (the most common electrical cause)
Open circuit from a broken signal wire or a backed-out connector pin
Exhaust leak ahead of the downstream sensor, pulling in atmospheric air and skewing the reading lean
Corroded or water-intruded sensor connector
Worn or aged downstream O2 sensor that no longer generates proper voltage
Failed sensor heater (often sets P0141 alongside P0137), keeping the sensor too cold to read correctly
Damage to the harness from aftermarket exhaust work
Catalytic converter damage altering the exhaust the sensor sees

Symptoms

Check Engine Light on, usually with normal drivability
Failed emissions test or a catalyst monitor that won't reach 'ready'
Faint exhaust smell on cold start if a leak ahead of the sensor is the cause
Minor loss of fuel economy
No noticeable power or idle change in most cases
Occasionally a companion heater-circuit code (P0141)

Diagnostic steps

1.Read live data for bank-1 sensor-2 voltage. A value pinned near 0V that won't move confirms a genuine stuck-low signal rather than a glitch.
2.Unplug the sensor and watch the PCM reading. If the reading changes meaningfully when disconnected, that helps separate a failing sensor from a harness short.
3.Inspect the signal wire end to end, especially where it runs near the chassis and exhaust, for chafe points shorting to ground.
4.Check the connector for corrosion, moisture, and backed-out pins. A poor connection often reads as an open or a low signal.
5.Listen and feel for an exhaust leak ahead of the sensor — a small leak introduces air that pulls the signal low without any real lean condition.
6.Confirm the sensor heater is working (battery voltage at the heater pin, key on). A dead heater keeps the sensor cold and can hold the signal low.
7.If wiring, connector, and exhaust all check out, the sensor is the likely answer — swap-test against bank 2 before buying parts.

Repair cost

$150 – $600

Most P0137 fixes are a downstream O2 sensor replacement at $150-400 depending on access. A wiring repair ranges from $50 for a single chafed wire to $200-500 for a damaged harness section. An exhaust leak repair varies widely depending on where it is. Rule out wiring and exhaust leaks before condemning the sensor — both are common and cheaper than a part swap that doesn't fix it.

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DIY vs shop

This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.