P0157 on a 2017 GMC Sierra 1500
Post-Cat O2 Sensor Low Voltage (Bank 2 Downstream)
P0157 on a 2017 GMC Sierra 1500 indicates post-cat o2 sensor low voltage (bank 2 downstream). It usually stays drivable short-term but should be diagnosed promptly. The most common cause is bank 2 downstream o2 signal wire shorted to ground or open (typically $80–$350). Confirm the root cause before replacing parts.
What does P0157 mean on a 2017 GMC Sierra 1500?
P0157 is the Bank 2 counterpart of P0137. The downstream oxygen sensor on the cylinder bank that does NOT contain cylinder number 1 is reporting a voltage below the calibrated minimum — typically under about 0.1 V — for an extended period. Sensor 2 sits after the catalytic converter, so on a warm engine it should hold a relatively steady 0.6–0.8 V rather than switching. A reading pinned low points at an open or shorted-to-ground signal circuit, a failed sensor, fresh air entering the exhaust ahead of the sensor, or a genuine lean condition on that bank.
The symptoms, causes, and diagnostic steps below describe P0157 itself, so they read the same on nearby GMC Sierra 1500 model years. Powertrain and trim details vary year to year — confirm the specifics against your own vehicle before buying parts.
Is it safe to drive a 2017 GMC Sierra 1500 with P0157?
In most cases a 2017 GMC Sierra 1500 stays drivable for short trips with P0157 active, but diagnose and repair it promptly. This is a moderate-severity code — ignoring it can lead to further damage or a failed emissions test.
What are the symptoms of P0157 on a 2017 GMC Sierra 1500?
- Check Engine Light is illuminated
- Catalyst readiness monitor will not complete
- Often no drivability symptoms at all
- Possible slight reduction in fuel economy
- Vehicle will fail emissions / smog testing
- Sometimes accompanied by P0174 if Bank 2 is genuinely lean
What causes P0157 on a 2017 GMC Sierra 1500?
| Cause | Likelihood | Estimated repair (USD) |
|---|---|---|
| Bank 2 downstream O2 signal wire shorted to ground or open | Most common | $80–$350 |
| Failed Bank 2 downstream O2 sensor (stuck low) | Most common | $150–$450 |
| Exhaust leak ahead of the Bank 2 downstream sensor drawing in fresh air | Common | $100–$500 |
| Corroded Bank 2 downstream O2 sensor connector | Common | $30–$200 |
| Damaged sensor pigtail from a previous exhaust or suspension repair | Occasional | $80–$300 |
| Genuine lean condition on Bank 2 from a vacuum leak A Bank-2-only lean condition usually means an intake leak specific to that bank. | Occasional | $80–$600 |
| Failed PCM input for the Bank 2 downstream circuit | Rare | $400–$1,500 |
Cost ranges are editorial estimates for parts and labor at an independent U.S. shop — not quotes. What you actually pay moves with your region, the shop's hourly rate, which engine you have, and how much diagnostic time the job takes. Dealer service departments typically sit above these ranges.
How to diagnose this on a 2017 GMC Sierra 1500
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Identify Bank 2, then identify Sensor 2
Two chances to go to the wrong part here. Bank 2 is the bank without cylinder number 1 — confirm which physical side that is in service information, because it varies by manufacturer. Sensor 2 is the sensor AFTER the catalytic converter on that bank, not the one in the manifold. Get either wrong and you replace a healthy sensor.
Tools: Vehicle-specific service information, Vehicle lift or jack stands
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Compare Bank 2 and Bank 1 fuel trims
This is the fastest way to tell a lying sensor from a real problem. If Bank 2 long-term fuel trim is near zero, the engine is fuelling correctly on that bank and the sensor or its wiring is at fault. If Bank 2 trim is high positive while Bank 1 is normal, you have a genuine bank-specific lean condition — find the leak rather than replacing the sensor.
Tools: Scan tool with per-bank fuel trim PIDs
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Disconnect the sensor and check for bias voltage
Unplug the Bank 2 downstream sensor and turn the key on. The scan tool PID should rise to the ECM's bias voltage, typically around 0.4–0.5 V. If it stays pinned near zero with the sensor disconnected, the signal wire is shorted to ground between the connector and the PCM, and no sensor will fix that.
Tools: Scan tool, Multimeter
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Inspect the harness under the vehicle
Follow the wiring from the sensor to the chassis connector. Look for insulation melted by exhaust contact, chafe points against the underbody, and corrosion or water inside the connector. On many V engines the Bank 2 downstream harness takes a longer route across the underside of the car, giving it more places to fail.
Tools: Flashlight, Inspection mirror, Electrical contact cleaner
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Look for exhaust leaks between the Bank 2 catalyst and sensor
A pinhole, a cracked weld, or a leaking flange gasket ahead of the sensor lets fresh air into the stream, and the sensor honestly reports the oxygen it finds — as a permanently low voltage. Listen along the pipe with the engine cold, when leaks are loudest before the metal expands.
Tools: Mechanic's stethoscope, Smoke machine (optional), Flashlight
NHTSA complaints & recalls for the 2017 GMC Sierra 1500
Owner-reported safety complaints and official recalls filed with the U.S. National Highway Traffic Safety Administration for the 2017 GMC Sierra 1500. Use these to gauge how common a problem is on your specific vehicle before you start chasing GMC Sierra 1500 diagnostics.
- POWER TRAIN 142
- ENGINE 62
- SERVICE BRAKES 127
- ELECTRICAL SYSTEM 60
- UNKNOWN OR OTHER 41
5 active recalls
- SERVICE BRAKES, HYDRAULIC:POWER ASSIST:VACUUM Sep 2019
General Motors LLC (GM) is recalling certain 2015-2017 Cadillac Escalade, 2014-2018 Chevrolet Silverado, GMC Sierra, 2015-2018 Chevrolet Suburban, Tahoe, GMC Yukon vehicles. The amount of vacuum created by the vacuum pump may decrease over time.…
NHTSA campaign 19V645000 - SERVICE BRAKES, HYDRAULIC:ANTILOCK/TRACTION CONTROL/ELECTRONIC LIMITED SLIP:WHEEL SPEED SENSOR/TONE RING Oct 2019
General Motors LLC (GM) is recalling certain 2015-2020 Chevrolet Suburban, Tahoe, and GMC Yukon, and 2014-2018 Chevrolet Silverado 1500 and GMC Sierra 1500 vehicles equipped with a 5.3-liter engine, a 3.08-ratio rear axle and four-wheel drive. If a wheel-speed sensor fails, whil…
NHTSA campaign 19V761000 - AIR BAGS:FRONTAL Sep 2016
General Motors LLC (GM) is recalling certain model year 2015-2017 Chevrolet Silverado 2500 HD, 3500 HD, Tahoe, Suburban, GMC Sierra 2500 HD and 3500 HD, GMC Yukon, GMC Yukon XL, Cadillac Escalade and Cadillac Escalade ESV vehicles and 2014-2017 Chevrolet Corvette, Silverado 1500…
NHTSA campaign 16V651000 - CHILD SEAT:TETHER: CONNECTOR/CLIP Aug 2017
General Motors LLC (GM) is recalling certain 2017 Chevrolet Silverado 1500, and GMC Sierra 1500 trucks. The owner's manual for the affected vehicles may be missing instructions on how to use the tether anchorage and child restraint anchorage systems. As such, these vehicles fai…
NHTSA campaign 17V487000
How do I fix P0157 on a 2017 GMC Sierra 1500?
- Replace the Bank 2 downstream O2 sensor with an OEM part
- Repair the shorted-to-ground or open O2 signal wire
- Repair exhaust leaks between the Bank 2 catalyst and its downstream sensor
- Clean or replace the corroded sensor connector
- Repair Bank 2 vacuum leaks if fuel trims confirm a real lean condition
Two chances to work on the wrong sensor
P0157 names a specific sensor in a specific place, and both halves of that name matter:
- Bank 2 — the cylinder bank without cylinder number 1. Which physical side that is depends on the manufacturer’s cylinder numbering. Look it up.
- Sensor 2 — the sensor after the catalytic converter, underneath the vehicle. Not the one in the exhaust manifold.
The wrong bank and the wrong sensor position are the two most common ways this repair gets done twice.
Fuel trim tells you whether to buy a sensor at all
Per-bank fuel trim is the deciding data point, and reading it takes less time than jacking the car up:
- Bank 2 trim near zero → the engine is fine, the sensor or its wiring is lying. Test the circuit, then replace the sensor.
- Bank 2 trim high positive, Bank 1 normal → the engine really is lean on that bank only. That pattern points at an intake gasket, a cracked vacuum line, or an injector problem specific to Bank 2. The sensor is doing its job.
- Both banks high positive → something common to both, such as a weak fuel pump or a large intake leak. Again, not the sensor.
Bank 2 sensors are not automatically the same job as Bank 1
The sensor part is usually identical to its Bank 1 twin. The access can be very different. On transverse V6s the Bank 2 exhaust often routes around the back of the engine, and the sensor may sit above a subframe or behind a heat shield that has rusted into place. Before assuming the job is a repeat of the Bank 1 sensor you did last year, check the labour time for this specific position.
Why this does not affect how the car drives
The downstream sensor grades the catalyst; the upstream sensor runs the fuelling. A dead Bank 2 downstream sensor mostly costs you the catalyst readiness monitor and the emissions test that depends on it. There is no mechanical harm in driving the car, and there is also no chance of the fault clearing itself — the monitor will keep failing until the circuit is repaired.
P0157 on a 2017 GMC Sierra 1500: frequently asked questions
What does diagnostic trouble code P0157 mean on a 2017 GMC Sierra 1500?
P0157 is the Bank 2 counterpart of P0137. The downstream oxygen sensor on the cylinder bank that does NOT contain cylinder number 1 is reporting a voltage below the calibrated minimum — typically under about 0.1 V — for an extended period. Sensor 2 sits after the catalytic converter, so on a warm engine it should hold a relatively steady 0.6–0.8 V rather than switching. A reading pinned low points at an open or shorted-to-ground signal circuit, a failed sensor, fresh air entering the exhaust ahead of the sensor, or a genuine lean condition on that bank.
What are the symptoms of P0157 on a 2017 GMC Sierra 1500?
Check Engine Light is illuminated. Catalyst readiness monitor will not complete. Often no drivability symptoms at all. Possible slight reduction in fuel economy. Vehicle will fail emissions / smog testing. Sometimes accompanied by P0174 if Bank 2 is genuinely lean
What causes P0157 on a 2017 GMC Sierra 1500?
Bank 2 downstream O2 signal wire shorted to ground or open (most-common). Failed Bank 2 downstream O2 sensor (stuck low) (most-common). Exhaust leak ahead of the Bank 2 downstream sensor drawing in fresh air (common). Corroded Bank 2 downstream O2 sensor connector (common). Damaged sensor pigtail from a previous exhaust or suspension repair (occasional). Genuine lean condition on Bank 2 from a vacuum leak (occasional). Failed PCM input for the Bank 2 downstream circuit (rare)
Is it safe to drive a 2017 GMC Sierra 1500 with P0157?
In most cases a 2017 GMC Sierra 1500 stays drivable for short trips with P0157 active, but it should be diagnosed and repaired promptly — this is a moderate-severity code. Ignoring it can lead to further damage or a failed emissions test.