P0137 Code on a GMC: O2 Sensor Circuit Low Voltage, Bank 1 Sensor 2 (GMC Guide)

P0137 on a GMC is GM's "O2 Sensor Circuit Low Voltage, Bank 1 Sensor 2" — the oxygen sensor behind the catalytic converter is reporting a signal stuck near zero. GM's tables call it a circuit "shorted to low," and GM's older truck tables add that it is found "by checking for a lean condition during steady throttle" — so leaks and a lean engine belong on the list beside wiring. GMC owners get three surprises from GM's own paperwork: on 2014–2018 Sierras and 2015–2018 Yukons, P0137 with three other O2 codes can be a software anomaly where the fix is clearing codes; on 2011–2013 Savana cutaways, rear sensors cracked from condensation and were recalled; and on the 2024 Sierra HD gas, GM's fix for a code list including P0137 is the front sensor.

What Does P0137 Mean on a GMC?

The rear oxygen sensor on a gasoline GMC is a conventional switching sensor: about 0.1 V when it sees oxygen, close to 0.9 V when it does not. Behind a working catalytic converter its signal is steadier than the front sensor's and normally sits toward the middle-to-high side. The engine control module (ECM) uses it to judge the converter (P0420/P0430) and to fine-tune fueling through post-catalyst fuel trim (P2096/P2097).

P0137 sets when that signal sits at the floor while the engine should be producing a normal mixture. The ECM cannot tell a signal wire grounded through chafed insulation from a sensor that genuinely sees oxygen because air is leaking into the exhaust. That is why the diagnosis has to separate wiring, leaks and the sensor — and why "replace the rear O2" is the wrong first move.

What GM's GMC Tables Say

In the 2016 table GM only runs the test in closed loop with the equivalence ratio between 0.9922 and 1.0137, so it is looking for a rear sensor that reads lean while the engine is being held at the correct mixture. GM's purpose line: "This DTC determines if the O2 sensor circuit is shorted to low." It is Type B — normally two failing trips before the light.

Which GMCs Set P0137

Any gasoline GMC with a rear oxygen sensor: Sierra and Sierra HD, Yukon and Yukon XL, Savana, Envoy, Canyon, Terrain and Acadia. On single-bank engines P0137 is simply the rear sensor. On V6 and V8 GMCs with a sensor behind each converter, the bank 2 twin is P0157. Duramax diesels and electric GMCs are outside this code.

The Sierra and Yukon Software PI (PIP5644)

GM's Preliminary Information PIP5644 (May 2019) is titled "E92 Controller with four O2 sensor DTC's P0132, P0137, P0152, P0157." It names the 2014–2018 GMC Sierra with the 4.3L LV3, 5.3L L83 and 6.2L L86, and the 2015–2018 GMC Yukon with the 5.3L and 6.2L, alongside the Chevrolet and Cadillac twins.

GM's condition: check engine light on and the vehicle runs rough within the first five minutes after it is started. GM's cause: "a software anomaly that allows all four DTC's P0132, P0137, P0152, P0157 to set." GM is explicit that all four codes must be in history for the PI to apply.

At publication GM was still investigating. The instruction: evaluate the vehicle for any other concern; if none is found, clear the codes and release the vehicle, using a unique 0.3-hour "Check and Clear Codes" labor operation. In plain terms, on these trucks the four-code pattern by itself is not a reason to buy four sensors. P0137 alone, or P0137 that keeps returning, still needs normal diagnosis.

The Savana Cutaway Sensor Recall (14096 and PI1006)

GM emission recall 14096 (revised as 14096A in May 2014) covers certain 2011–2013 GMC Savana and Chevrolet Express cutaways with gasoline engines. GM's condition: the oxygen sensor "may fracture if condensation from the catalytic converter enters the O2 sensor and causes a sudden temperature change," turning on the check engine light. Dealers inspect and, if needed, replace both rear sensors — bank 1 sensor 2 and bank 2 sensor 2 — with a second-design sensor (GM part 12637297, replacing first-design 12656071 or 12612571) and reprogram the ECM.

The earlier PI1006 (June 2013) described the same thing on 2011–2013 Savana cutaways with the 4.8L or 6.0L V8 built before November 26, 2012: moisture splashing on hot sensors and cracking them. GM noted the new sensors are wired differently internally and require ECM reprogramming — so fitting the new part without the calibration is not a complete repair. PI1006's keyword list includes P0137, P0138, P0157 and P0158.

The recall is more than a decade old, so for practical purposes most involved vans will have been done, but a dealer VIN check is free.

The 2024 Sierra HD Bulletin (24-NA-042)

GM bulletin 24-NA-042 (revised April 2024) covers the 2024 Sierra 2500HD/3500HD with the 6.6L gas V8 (L8T). Its code list includes P0300, the front heater codes, P0132, P0135, P0137, P0155, P0171 and P0172. GM's April revision specifically added the P0132 and P0137 information.

The cause is a mis-routed bank 1 sensor 1 wiring harness touching the exhaust pipe; the correction is to replace the bank 1 front sensor and route its wiring away from the exhaust, and GM notes the circuit's fuse may be open. So on these trucks a rear-sensor code can trace to the front sensor's wiring — the opposite of what a generic code definition suggests.

Acadia and Canyon Bulletins

• 2013–2015 Acadia 3.6L — PIT5336. P0137 is on the list of O2 and purge codes caused by the bank 1 sensor harness chafing on the A/C hose coupling behind the engine, sometimes with the Emission 1 fuse open. Repair and re-secure the harness.
• 2016 Acadia and 2017 Acadia Limited 3.6L — 18-NA-009. P0137 appears with P0131, P0132, P0133, P0032, P0171 and P2096 when power steering fluid leaks onto the bank 1 O2 harness. GM replaces the hose, the bank 1 front sensor and the engine harness.
• 2015–2017 Canyon 2.5L and 2017 Acadia 2.0T — PIP5529B. P0137 with P0131, P0171 and others can trace to loose intake manifold bolts — a lean engine leaves oxygen for the rear sensor to see. Re-torque with threadlocker per GM.

Exhaust Leaks: The Other Way to Read Low

GM bulletin 20-NA-065 (August 2022) covers 2000–2022 GM gasoline cars and trucks, GMC included, with a check engine light and fuel trim or oxygen sensor codes — P0137 among them. When normal diagnosis does not find the cause and a leak is suspected, GM recommends its variable pressure smoke leak detector, an ultrasonic leak tester, or soapy water with low-pressure air into the tailpipe, and notes these are "very good for finding small leaks around the O2 sensor embossments." On a truck, check the converter flanges and sensor boss.

Where Bank 1 Sensor 2 Is on a GMC

• Sierra, Yukon, Savana and Envoy V8s, the 4.3L V6 and the Sierra HD 6.6L gas: bank 1 is the driver side; sensor 2 is behind the driver-side converter.
• Acadia 3.6L and Terrain 3.6L: bank 1 is the rear, firewall-side bank; its rear sensor sits after that bank's converter under the vehicle.
• Single-bank engines (Terrain, Acadia and Canyon four-cylinders, the 2.7T, Envoy 4.2L): one rear sensor, after the converter.

Some exhaust layouts merge the banks; confirm sensor positions for your VIN in service information.

Symptoms of P0137

• Check engine light on
• Often no drivability change — the rear sensor does little fuel control
• Rough running in the first five minutes on a 2014–2018 Sierra or 2015–2018 Yukon when all four PIP5644 codes are present
• Misfire or fuel trim codes alongside on a 2024 Sierra HD gas (24-NA-042)
• Catalyst monitor not completing; possible P0420 or P2096/P2097 alongside
• Failed emissions inspection because of the light or incomplete monitors

Causes and How to Confirm Each

How Is P0137 Diagnosed on a GMC?

1. Record every code. On a 2014–2018 Sierra or 2015–2018 Yukon, check for P0132, P0152 and P0157 in history (PIP5644).
2. Check the VIN for recall 14096 (Savana cutaway), 24-NA-042 (2024 Sierra HD gas), PIT5336 or 18-NA-009 (Acadia 3.6L) and PIP5529B (Canyon 2.5L, Acadia 2.0T).
3. Read fuel trims and the front sensor. If the engine is lean overall, fix that first.
4. Watch the rear sensor fully warm in closed loop, then add fuel briefly. A good rear sensor climbs toward 0.8–0.9 V within a few seconds.
5. Leak-test the exhaust from the converter back past the sensor, as 20-NA-065 describes.
6. Inspect the connector and harness for water, corrosion, chafing and heat damage.
7. Unplug and test the circuit for a short to ground and continuity to the ECM.
8. Replace the sensor only when wiring and exhaust check out — and reprogram the ECM where a bulletin requires it.
9. Clear and verify over two trips.

Parts and Cost

GM Documents Relevant to P0137 on a GMC

Have a dealer check your VIN against current bulletins rather than relying on any article, including this one.

What Other P0137 Pages Get Wrong

• "Replace the rear O2 sensor." GM's GMC documents point at software, leaks, intake bolts and wiring — sometimes the front sensor's wiring — before the rear sensor.
• "It means the catalytic converter is bad." A worn converter usually makes the rear sensor switch, which sets P0420 — not a signal stuck below 50 mV.
• Treating one code like four. PIP5644 applies only when all four O2 codes are in history.
• Fitting a new sensor without the calibration. On recalled Savana cutaways, GM's new rear sensors are wired differently and need ECM programming.
• Ignoring exhaust leaks. GM wrote 20-NA-065 because small leaks near sensor bosses fool oxygen sensors.

Frequently Asked Questions

Can I drive my GMC with P0137?

Usually, for a short time — the rear sensor does little fuel control. But the catalyst monitor will not complete, so an emissions inspection will fail until it is fixed.

Is P0137 the upstream or downstream sensor?

Downstream — Bank 1 Sensor 2, after the catalytic converter. The upstream low-voltage code is P0131.

My Sierra has P0132, P0137, P0152 and P0157. Do I need four sensors?

On a 2014–2018 Sierra or 2015–2018 Yukon, GM's PIP5644 describes that exact set as a software anomaly. If no other concern is found, GM's instruction was to clear the codes. Ask a dealer to check current information for your VIN.

Can an exhaust leak cause P0137?

Yes. Air drawn in ahead of the rear sensor drives its reading low. GM's 20-NA-065 recommends smoke, ultrasonic or air-and-soap testing.

Does my Savana cutaway have the sensor recall?

Certain 2011–2013 Savana cutaways with gasoline engines are covered by recall 14096 for rear sensors that crack from condensation. A dealer can check the VIN for free.

What is the opposite code?

P0138 — the same rear sensor reading too high. The bank 2 version of P0137 is P0157.

Is there a Cadillac version of this guide?

Yes — our Cadillac P0137 guide covers the Escalade side of PIP5644.