P0139 on 2013-2016 Dodge Dart 1.4L Turbo: Causes and Fixes for Slow O2 Sensor Response

What's Unique About the 2013-2016 Dodge Dart

The 1.4L MultiAir Turbo engine is shared across several Fiat-Chrysler (FCA) vehicles, including the Fiat 500 Abarth and Jeep Renegade, which also report this code. On this platform, while the P0139 code is common across many vehicles, owners should be particularly aware of potential exhaust leaks near the turbocharger's V-band clamp or the downpipe's flex pipe, which can alter sensor readings and trigger this code. Additionally, some owners and technicians recommend replacing both the upstream and downstream oxygen sensors at the same time, even if only one has failed, to prevent issues caused by mismatched sensor switching speeds between a new and an old sensor.

Symptoms You May Notice

• Check Engine Light is illuminated
• Reduced fuel economy
• Vehicle may fail an emissions test
• In rare cases, slight hesitation or rough running during deceleration
• Strong exhaust odor due to a potentially rich fuel mixture

Most Likely Causes

1. Failing Downstream Oxygen Sensor (Bank 1, Sensor 2) 🔴 High Probability Oxygen sensors are wear items that degrade over time due to constant exposure to high heat and exhaust gases. Contamination from oil or coolant can also accelerate failure. Many owners report this as the definitive fix.
   How to confirm: Use a scan tool to graph the voltage of the B1S2 sensor. A healthy downstream sensor's voltage should fluctuate slowly and stay relatively stable (e.g., 0.6-0.8V) at steady RPM. If the voltage is stuck, flat, or responds very sluggishly to sharp throttle changes, the sensor is likely bad.
   Typical fix: Replace the downstream oxygen sensor. It is located under the car, after the catalytic converter. Using an O2 sensor socket is highly recommended.
   Est. part cost: $50-$135
2. Exhaust Leak 🟡 Medium Probability The 1.4L Turbo platform has documented owner complaints of exhaust leaks, particularly from the V-band clamp between the turbo and downpipe or the woven flex pipe section. An exhaust leak before the sensor can introduce outside air, causing incorrect readings and triggering a slow response code.
   How to confirm: Visually inspect the exhaust system from the engine to the downstream O2 sensor for soot marks, cracks, or loose connections. Listen for audible hissing or ticking sounds, especially when the engine is cold. A shop can perform a smoke test to pinpoint hard-to-see leaks.
   Typical fix: Repair the leak by replacing the faulty gasket, tightening clamps, or having a muffler shop weld in a new flex pipe section.
   Est. part cost: $10-$300
3. Damaged Wiring or Connector ⚪ Low Probability The sensor wiring runs under the vehicle and is exposed to heat, road debris, and moisture, which can cause corrosion, melting, or physical damage over time.
   How to confirm: Visually inspect the wiring harness and connector for the downstream O2 sensor. Look for any signs of melting, chafing, corrosion in the pins, or broken wires. Check for pushed-back terminals inside the connector.
   Typical fix: Repair the damaged section of the wiring harness or replace the connector pigtail. Ensure the wiring is properly secured away from hot exhaust components.
   Est. part cost: $15-$50

Rare But Worth Checking

• Leaking Fuel Injectors: If the engine is running excessively rich due to a leaking injector, it can foul the O2 sensor and affect its readings. This would typically be accompanied by other codes like P0172 (System Too Rich).
• Failing Powertrain Control Module (PCM): In very rare instances, the fault may lie with the PCM's internal circuitry for processing the sensor's signal. This should only be considered after all other possibilities have been exhaustively ruled out. Software updates may be required to fix overly sensitive diagnostic thresholds.

Diagnosis Steps

1. Scan for Codes: Use an OBD-II scanner to confirm P0139 is the only code present. If other codes exist (e.g., for misfires, fuel trim, or heater circuits), address them first as they can be the root cause.
2. Check for Exhaust Leaks: With the engine running (and cool enough to work around), carefully check for leaks between the engine and the downstream sensor. Listen for unusual sounds and look for black soot trails that indicate a leak. Pay close attention to the turbo downpipe connection and flex pipe.
3. Visual Inspection of Wiring: Inspect the downstream O2 sensor's wiring harness and connector for any obvious damage, such as melting, chafing, or corrosion. Ensure the connector is securely plugged in.
4. Analyze Live Data: Use a scanner with live data capabilities to monitor the Bank 1 Sensor 2 voltage. At a steady 2500 RPM, the voltage should be relatively stable. During deceleration (fuel cut-off), the voltage should drop quickly towards 0V. If it responds very slowly or remains flat, the sensor is the primary suspect.
5. Test the Sensor: If the wiring and exhaust are confirmed to be good, the most likely cause is the sensor itself. Replacement is the next logical step.
6. Final Check: After replacing the sensor, clear the codes and perform a drive cycle to ensure the code does not return.

Parts You'll Likely Need

• Downstream Oxygen Sensor (Bank 1, Sensor 2) (OEM #68142340AA) — This is the most common failure point for a P0139 code. The sensor degrades over time and loses its ability to respond quickly. Community consensus strongly favors OEM (Mopar) or OE-supplier (NTK/NGK, Denso) parts for reliability.
  Trusted brands: Mopar, NTK, Denso, Bosch, Walker Products
  OEM price range: $130-$150
  Aftermarket price range: $50-$90

Related Codes That Often Appear With This One

• P0140 — P0140 (O2 Sensor Circuit No Activity Detected) can appear with P0139 if the sensor becomes completely unresponsive.
• P0141 — P0141 (O2 Sensor Heater Circuit Malfunction) often accompanies sensor performance codes, as a faulty heater can cause the slow response.

Technical Service Bulletins (TSBs) & Recalls

• No specific TSB directly addresses the P0139 code for the 2013-2016 Dodge Dart 1.4L. However, FCA has issued TSBs for other models (e.g., TSB 18-059-16 for 2011 Chrysler/Dodge vans) that involve PCM software updates to correct various O2 sensor heater circuit codes, indicating that software can be a factor in related faults. TSB 18-009-15 Rev. G also calls for a PCM reflash on 1.4L Darts for other O2 sensor codes like P0141, reinforcing that software updates are a valid repair step for this system.

Platform-Specific Known Issues

• Some owners on forums like dodge-dart.org report that replacing only the downstream sensor can sometimes lead to a P0420 (Catalyst Efficiency) code, because the new sensor's switching rate is much faster than the old, tired upstream sensor. For this reason, replacing both sensors at once is sometimes recommended.

Mechanic-Grade Diagnostic Values

• Downstream O2 Sensor Signal Voltage (PCM Biased) — expected: Fluctuating between 2.5 volts and 3.5 volts.. Failure: Voltage is stuck, flat, or responds very slowly to throttle changes.
• Downstream O2 Sensor Heater Resistance — expected: Approximately 9 Ohms at 20°C (68°F).. Failure: Resistance is significantly higher (e.g., >40 Ohms) or shows an open circuit (infinite resistance).
• O2 Sensor Circuit-to-PCM Resistance — expected: Below 5.0 Ohms.. Failure: Resistance is above 5.0 Ohms, indicating corrosion or a damaged wire in the harness.

Hidden / Shadow Codes Worth Checking

• Mode $06 Data: While not a 'shadow code,' Mode $06 provides the raw results of the PCM's self-tests before a DTC is set. A technician can view the test results for the 'O2 Sensor Response Rate' monitor. This data will show the actual measured response time, a minimum threshold, and a maximum threshold. Seeing a value that is close to the failure threshold can confirm a degrading sensor even if the Check Engine Light is not yet on. (see via A professional scan tool with Mode $06 capability is required. The specific Test ID (TID) and Component ID (CID) vary by manufacturer but will be labeled related to O2 sensor performance.)

Scan Tool Commands That Help

• wiTECH (Chrysler/FCA Dealer Tool): PCM Reprogramming / Flash — Use when TSB 18-009-15 applies. This software update addresses multiple drivability issues and diagnostic trouble codes, including those for O2 sensor circuits (like P0141). An outdated PCM calibration may have thresholds that are too sensitive, causing a P0139 code to be set erroneously. Always check for the latest software before replacing hardware.
• wiTECH: Cruise Control Learn Procedure — This procedure is required after reprogramming the PCM, as per FCA service bulletins. Failing to perform this can leave unrelated DTCs or system faults.

Wiring & Ground Locations

• PCM Location — Right rear corner of the engine compartment.. This is the termination point for the O2 sensor wiring. When checking for continuity or shorts, testing will be done between the sensor connector and the PCM connector.
• Engine Ground Strap — A braided or ribbon cable connecting the engine block to the chassis, often located on the passenger side of the engine bay connecting to the strut tower or frame rail.. A corroded or loose engine ground can cause a host of electrical issues, including erratic sensor readings. The PCM relies on a stable ground reference for all its sensors; a poor ground can create a voltage offset that makes the O2 sensor signal appear slow or incorrect.
• O2 Sensor 1/2 Connector (C104) — Underneath the vehicle, on the exhaust pipe after the catalytic converter. The connector is part of the sensor's pigtail.. This is the primary point of inspection for physical damage, corrosion, or pushed-back pins. The pinout includes power for the heater, ground, and the signal return wire.

Real Owner Repair Stories

• dodge-dart.org user 'alpinegreenneon' (2013 Dodge Dart 1.4L Turbo) — A sequence of codes appeared. First a misfire, then P0137 (O2 Sensor Circuit Low Voltage B1S2) after replacing plugs/coil. After replacing the B1S2 sensor, a new code P2096 (Downstream Fuel Trim System 1 Lean) appeared.
  ❌ Tried (didn't work) Replacing the downstream O2 sensor did not fully resolve the check engine light, as a new, related code appeared immediately after.
  ✅ What actually fixed it The crucial advice given was that these engines are notoriously picky about O2 sensor brands. The user was warned, 'Hope you didn't buy a Bosch sensor. These engines only like Mopar or NTK O2 sensors.' The implication is that using an incompatible aftermarket sensor caused the subsequent P2096 code, and the fix is to use the correct OEM or OE-equivalent brand.

"I Checked Everything" — The Actual Cause

• A common scenario for a recurring P0139 on this vehicle involves a technician performing an exhaust smoke test and finding no leaks. The technician then replaces the downstream O2 sensor, but the code returns. The actual root cause is often one of two things missed by standard procedure: 1) The use of an incompatible aftermarket O2 sensor brand (e.g., Bosch instead of Mopar/NTK) which has a different response characteristic, or 2) The need for a PCM software update per TSB 18-009-15 to adjust the sensitivity of the O2 sensor monitoring logic.

OEM Part Supersession History

• 68142340AA → No supersession found. — N/A
  Heads up: This part number appears to be consistent for the 2013-2016 Dart 1.4L and is also used on other FCA vehicles with the same engine, such as the Fiat 500L.

Model Year Variations Within This Range

• 2014-2016: Starting in model year 2014, the 1.4L Turbo engine was no longer the primary engine for most trims. It was relegated mainly to the fuel-economy-focused 'Aero' model. Most SXT, Limited, and GT trims received the 2.4L engine instead. This is critical for diagnosis, as the 2.4L engine has its own set of common issues and TSBs.
• 2014, 2015, 2016: FCA TSB 18-009-15, which involves a PCM reflash, lists different symptoms and addressed DTCs for different model years. For example, 'P113D - O2 Sensor 1/1 Slow Response' was a condition specifically listed for the 2015 model year, indicating software logic and monitoring thresholds evolved during the production run.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• MultiAir Actuator ('Brick') Failure 🔴 High — Common as mileage exceeds 60,000-80,000 miles. Often preceded by misfire codes (P030x) and specific actuator codes (e.g., P1067, P106B).
• DDCT (Dual Dry Clutch Transmission) Failure 🔴 High — Affects automatic models. Issues range from faulty hydraulic actuators and solenoids to complete transmission failure. Symptoms include 'Service Transmission' warnings and 'Gear Unavailable' messages.
• Excessive Oil Consumption 🟠 Medium — Many owners report consuming a quart of oil every 1,000-3,000 miles. Requires frequent oil level checks to prevent engine damage.
• Turbocharger Failure 🔴 High — Less common than other issues, but some owners have required turbo replacement, sometimes under powertrain warranty around 50,000 miles.
• Bluetooth/Hands-Free Module Failure 🟡 Low — A very common annoyance where the Uconnect system gets stuck on 'Loading Hands-Free' and becomes unresponsive.
• Sticking/Seized Rear Brake Calipers 🟠 Medium — The parking brake mechanism on the rear calipers is prone to seizing, causing the rear brakes to drag.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this repair, a used part is almost never a smart choice for the oxygen sensor itself, as it is a wear-and-tear component with a finite lifespan. However, sourcing a used wiring harness connector pigtail from a junkyard is a viable and cost-effective option if the original connector is melted, corroded, or physically broken.

Donor-vehicle mileage cap: roughly under 120000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For a connector pigtail, inspect for plastic that is not brittle or cracked.
• Ensure the locking tab is intact.
• Check for clean, corrosion-free electrical pins inside the connector.
• Verify the attached wires are flexible and the insulation is not cracked or melted.

OEM-only on this vehicle (don't cheap out):

• Oxygen Sensor: Due to the PCM's sensitivity, it is highly recommended to use either the OEM Mopar sensor or the original equipment supplier, which is NTK (also known as NGK).

Aftermarket brands forum-validated for this vehicle:

• NTK
• Denso

Brands owners have reported issues with on this vehicle:

• Bosch: Forum members have specifically reported issues with Bosch sensors on this platform, where replacing a faulty sensor with a Bosch unit led to different but related trouble codes.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0140 — Often appears alongside P0139, indicating a lack of activity in the same downstream oxygen sensor circuit.
• P0141 — Downstream O2 sensor heater circuit fault; often triggered by the same sensor failure or addressed by PCM reflash TSB 18-009-15 Rev. G.
• P0171 — Lean fuel trim code that can appear with P0139 if an exhaust leak or sensor failure is affecting the air-fuel ratio calculations.
• P0172 — Rich fuel trim code; may occur if the downstream sensor is sluggish or if the vehicle is producing a strong exhaust odor.
• P0420 — Catalyst Efficiency code that can be triggered after replacing a slow P0139 sensor if the upstream sensor is also aged.
• P0300 — Random misfire code; related to broader engine health issues like MultiAir actuator failure which can impact emissions readings.

Frequently Asked Questions