P0157 on Ram vehicles
Post-Cat O2 Sensor Low Voltage (Bank 2 Downstream) — what it means on a Ram, whether it's safe to drive, and the fixes by model and year.
P0157 on a Ram means post-cat o2 sensor low voltage (bank 2 downstream). Most vehicles stay drivable short-term, but diagnose it promptly. The most common cause is bank 2 downstream o2 signal wire shorted to ground or open (typically $80–$350). Pick your Ram model below for its known failure patterns, recalls, and TSBs.
What does P0157 mean on a Ram?
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.
P0157 is a standardized OBD-II code, so its definition is the same on every Ram. What differs by model and engine is which cause is most likely — pick your Ram model below for a diagnosis tuned to its known failure patterns, recalls, and TSBs.
Is it safe to drive a Ram with P0157?
In most cases a Ram 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. Exact tolerance depends on the model and engine.
What causes P0157 on a Ram?
| 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 |
Repair costs are typical US ranges and vary by Ram model, model year, and labor rate. A diagnostic trouble code is a symptom, not a guaranteed failed part — confirm the root cause before replacing anything.
P0157 by Ram model
Select your Ram model and year for a P0157 diagnosis tuned to that vehicle's failure patterns, recalls, and TSBs.
Ram 1500
1,537 NHTSA owner complaints · 35 recalls on record across the years covered below.
Complaint and recall counts are NHTSA totals for the model years covered on this site, not counts specific to P0157.
P0157 on other makes
Other codes on Ram vehicles
P0157 on a Ram: frequently asked questions
What does diagnostic trouble code P0157 mean on a Ram?
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. P0157 is a standardized OBD-II code, so the definition is the same on every Ram — which cause is most likely varies by model and engine.
What are the symptoms of P0157 on a Ram?
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 Ram?
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 Ram with P0157?
In most cases a Ram 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. Exact tolerance depends on the model and engine.