Aged or contaminated downstream oxygen sensor (bank 1 sensor 2); Exhaust leaks between the catalytic converter and the downstream sensor; A failing catalytic converter that no longer stores oxygen properly; Wiring damage or corrosion at the downstream sensor connector; A stuck-open or leaking fuel injector affecting exhaust oxygen content; An intake manifold vacuum leak that skews the air-fuel mixture; A faulty powertrain control module (PCM) driver circuit, though this is uncommon

DTC codes / Chrysler codes / P1139

P1139 · ChryslerHO2S Insufficient Switching Bank 1 Sensor 2

Q: What does code P1139 mean?

HO2S Insufficient Switching Bank 1 Sensor 2. P1139 on Chrysler vehicles means the downstream oxygen sensor (HO2S) on bank 1 is not switching voltage fast enough for the powertrain control module (PCM) to confirm proper catalytic converter efficiency. The PCM monitors the sensor's activity after the converter and sets this code when the signal remains too steady or switches too slowly over a calibrated test period.

P1139 on Chrysler vehicles means the downstream oxygen sensor (HO2S) on bank 1 is not switching voltage fast enough for the powertrain control module (PCM) to confirm proper catalytic converter efficiency. The PCM monitors the sensor's activity after the converter and sets this code when the signal remains too steady or switches too slowly over a calibrated test period.

SystemPowertrain

Code typeChrysler specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illumination of the check engine light, often with no other symptoms
A slight decrease in fuel economy over time
Occasional rough idle or hesitation when the engine is cold
Failed emissions inspection due to the stored code
In rare cases, a sulfur or rotten-egg smell from the exhaust

Common causes, most likely first

Aged or contaminated downstream oxygen sensor (bank 1 sensor 2)
Exhaust leaks between the catalytic converter and the downstream sensor
A failing catalytic converter that no longer stores oxygen properly
Wiring damage or corrosion at the downstream sensor connector
A stuck-open or leaking fuel injector affecting exhaust oxygen content
An intake manifold vacuum leak that skews the air-fuel mixture
A faulty powertrain control module (PCM) driver circuit, though this is uncommon

How to diagnose and fix it

Scan all modules and record freeze-frame data to confirm the code and check for related oxygen sensor or catalyst codes
Inspect the downstream oxygen sensor wiring and connector for chafing, corrosion, or loose pins
Perform a visual and smoke test of the exhaust system from the converter back to the sensor
Graph the downstream oxygen sensor voltage on a scan tool to verify slow or lazy switching
Check fuel trims and injector balance to rule out rich or lean conditions that mimic a bad sensor
Replace the downstream oxygen sensor if it is slow or unresponsive and the wiring and exhaust are intact
Clear the code and complete a drive cycle to verify the repair and confirm the monitor runs

What the downstream sensor is really telling you

A lazy downstream oxygen sensor often passes a simple resistance check but still fails the PCM's switching test, so graphing live voltage is more reliable than a multimeter alone.
Exhaust leaks upstream of the downstream sensor pull in outside air and can make a healthy sensor look slow, leading to unnecessary sensor replacement.
A catalytic converter that is just beginning to degrade can set P1139 before any P0420 catalyst efficiency code appears, so the converter should be evaluated if the sensor is new.
Fuel system problems such as a leaking injector or high fuel pressure change exhaust oxygen content and can trigger this code even when the sensor and converter are fine.
On some Chrysler models, a weak battery or poor ground can cause erratic sensor voltage readings that mimic a failing downstream oxygen sensor.

Can I keep driving with P1139?

The vehicle remains safe to drive in most cases because this code mainly affects emissions and fuel economy, but avoid ignoring it for long periods. Prolonged driving with a slow downstream sensor can mask a failing catalytic converter and lead to more expensive repairs, so schedule diagnosis soon.

Tools that help

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Guidance is general and written for Chrysler vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.