P0138 on 2008-2023 Dodge Challenger: O2 Sensor High Voltage Causes and Fixes

What's Unique About the 2008-2023 Dodge Challenger

For the Dodge Challenger and its LX platform mates (Charger, 300), this code is a straightforward and common issue. A key vulnerability is the O2 sensor wiring harness, which is often routed near hot exhaust and transmission components. It is frequently reported that the harness melts or chafes, causing the signal wire to short to the heater circuit's power wire, which triggers the P0138 code. Owners consistently report that using cheap, generic O2 sensors often leads to the code returning quickly, making it crucial to use OEM (Mopar) or high-quality OE-equivalent brands like NTK or Denso.

Generation note: The 2008-2023 model years cover the third generation (LC) of the Dodge Challenger. The interpretation of code P0138 is consistent across all engine options (3.5L V6, 3.6L V6, 5.7L Hemi, 6.1L Hemi, 6.2L Hemi, 6.4L Hemi) within this generation. Bank 1 is the driver's side on V8s and the passenger's side on V6s.

Symptoms You May Notice

• Check Engine Light is on
• Failed emissions test
• Decreased fuel economy
• Rough or unstable idle
• Hesitation or sluggish acceleration
• Strong exhaust odor or smell of gasoline

Most Likely Causes

1. Faulty Bank 1, Sensor 2 Oxygen Sensor 🔴 High Probability → Shop Oxygen Sensor Oxygen sensors are wear-and-tear items that degrade over time due to extreme heat, exhaust contaminants, and vibration. They have a finite lifespan, and internal failure can cause the voltage to stick high.
   How to confirm: Use an OBD-II scanner to monitor the live data for the B1S2 O2 sensor. If the voltage is stuck high (e.g., >0.9V) and does not fluctuate as you drive (e.g., coasting vs. accelerating), the sensor has likely failed internally.
   Typical fix: Replace the Bank 1, Sensor 2 oxygen sensor. It is located after the catalytic converter on the driver's side (V8s) or passenger's side (V6s). Use a quality brand like Mopar or NTK to prevent recurrence.
   Est. part cost: $40-$160
2. Damaged Wiring or Connector 🟡 Medium Probability The O2 sensor wiring is routed near the hot exhaust system and transmission. The harness can melt, become brittle and crack, or get damaged by road debris, leading to a short circuit to voltage. This is a very common failure point on the Challenger and its platform mates.
   How to confirm: Visually inspect the entire wiring harness from the O2 sensor to the main engine harness. Look for melted plastic, chafed wires, or corrosion in the connector. A common failure spot is where the harness may rest on the transmission. 🎬 See this walkthrough on finding and fixing melted wiring harnesses Use a multimeter to check for a short to voltage on the signal wire.
   Typical fix: Repair the damaged section of the wiring harness or replace the connector pigtail. Secure the harness away from direct contact with the exhaust using zip ties.
   Est. part cost: $10-$50
3. Engine Running Rich ⚪ Low Probability While not specific to the Challenger, any issue causing a rich fuel mixture (too much fuel, not enough air) can cause the downstream O2 sensor to read high correctly. This could be due to leaking fuel injectors or excessive fuel pressure.
   How to confirm: Look for other diagnostic trouble codes related to the fuel system (e.g., P0172 - System Too Rich). Check fuel pressure and inspect for leaking fuel injectors or a faulty fuel pressure regulator.
   Typical fix: Diagnose and repair the root cause of the rich condition, such as replacing a leaking fuel injector.
   Est. part cost: $50-$400+

Rare But Worth Checking

• Exhaust Leak Before the Sensor: An exhaust leak before the *upstream* O2 sensor can trick the system into adding too much fuel, causing a rich condition that the downstream sensor then reports as high voltage. This is less common than a direct sensor or wiring failure for this code.
• Powertrain Control Module (PCM) Failure: In very rare cases, the PCM itself can have a faulty driver circuit, causing it to misinterpret the sensor's signal. Some TSBs recommend a software update to fix erroneous O2 sensor codes. This should only be considered after all other possibilities have been exhaustively ruled out.

Diagnosis Steps

1. Confirm the code P0138 is present using an OBD-II scanner. Check for any other codes.
2. Observe live data on the scanner for the Bank 1, Sensor 2 (B1S2) O2 sensor. Confirm if the voltage is stuck high (consistently >0.9V).
3. Perform a thorough visual inspection of the B1S2 O2 sensor and its wiring harness. Pay close attention to where the harness passes over the transmission or near the exhaust manifold for signs of melting, chafing, or loose connections.
4. If wiring looks good, disconnect the sensor. With the key on, engine off, check the harness-side connector for voltage. A short to power on the signal wire would cause this code.
5. Check for relevant Technical Service Bulletins (TSBs) for your vehicle's year and engine. For example, TSB 18-071-22 REV. B suggests a PCM software update for some models with O2 sensor codes.
6. If the wiring and PCM software are ruled out and the voltage is stuck high on live data, the O2 sensor itself is the most likely culprit.
7. Replace the Bank 1, Sensor 2 oxygen sensor using a quality Mopar or NTK part.
8. Clear the code and perform a drive cycle to ensure the code does not return.

Parts You'll Likely Need

• Oxygen Sensor (Bank 1, Sensor 2) (OEM #Mopar 56029049AA (example for 5.7L, check VIN for exact fit)) — This is the component that generates the voltage reading. It is a common wear item and the most frequent cause of the P0138 code.
  Trusted brands: Mopar, NTK, Denso, Bosch
  OEM price range: $100-$160
  Aftermarket price range: $40-$90

Related Codes That Often Appear With This One

• P0038 — P0038 is for 'HO2S Heater Control Circuit High (Bank 1, Sensor 2)'. Since the heater and sensor elements are in the same physical component, a failure or wiring short that causes P0138 can often trigger a heater circuit code as well.
• P0137 — P0137 is for 'O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)'. Seeing this code intermittently with P0138 could point to an erratic sensor or a wiring problem causing wild voltage swings.
• P0172 — P0172 means 'System Too Rich (Bank 1)'. If the P0138 is being caused by a legitimate rich running condition, you will likely see this code as well, which points to the underlying fuel delivery problem.

Technical Service Bulletins (TSBs) & Recalls

• TSB 18-071-22 REV. B: Recommends a PCM software update for some 5.7L models to address various O2 sensor related codes, including P0138.
• TSB Bulletin #25-002-14: A manufacturer service bulletin for related models notes that P0138 specifically indicates the 1/2 O2 sensor is shorted to voltage.
• TSB Bulletin #25-003-13: This bulletin lists P0138 as a condition where the 1/2 O2 sensor is shorted to voltage, requiring diagnostic attention to the electrical system.
• TSB Bulletin #25-004-12: Documentation regarding fuel and electrical systems identifies P0138 as an O2 sensor 1/2 shorted to voltage condition.

Platform-Specific Known Issues

• Emissions Recall V86: Some 2015-2017 Challenger Hellcat models were recalled for catalytic converter issues. The fix, performed by a dealer, includes replacing both catalytic converters, all four oxygen sensors, and updating the PCM software. Owners of these vehicles should check if this free repair has been performed.
• Melted Wiring Harness: A recurring theme in owner forums for Challengers, Chargers, and 300s is the O2 sensor harness sagging or coming loose and melting on the hot transmission case or exhaust pipe, causing wires to short together. This should be the first visual check before buying parts.

Mechanic-Grade Diagnostic Values

• O2 Sensor Heater Element Resistance — expected: 2.0 to 30.0 Ohms at 70°F (21°C). Specifically, 5-9 Ohms is common for NTK sensors.. Failure: A reading of infinite resistance (OL - Open Loop) or near-zero Ohms (short circuit) indicates a failed heater element.
• O2 Sensor Signal Circuit Bias Voltage (KOEO) — expected: Approximately 5.0 Volts on the signal wire at the harness-side connector with the sensor disconnected.. Failure: No voltage or significantly lower voltage suggests a problem with the PCM or the wiring between the PCM and the sensor connector.
• Downstream O2 Sensor Live Data (Warm Engine, Steady RPM) — expected: A relatively stable voltage, typically around 0.5V - 0.7V, if the catalytic converter is efficient.. Failure: Voltage is stuck high, consistently reading above 0.9V, which triggers the P0138 code.

Scan Tool Commands That Help

• wiTECH (or equivalent professional scanner): O2 Sensor Heater Actuation Test — This command forces the O2 sensor's internal heater on, allowing a technician to verify the integrity of the heater circuit (power, ground, and control) by monitoring voltage or current draw, without waiting for the PCM to command it on during a cold start.
• wiTECH (or equivalent J2534 device): PCM Flash / Reprogramming — Used to apply a software update from a Technical Service Bulletin (TSB), such as TSB 18-071-22 REV. B, which can resolve erroneously set O2 sensor codes by modifying the PCM's monitoring logic.

Wiring & Ground Locations

• O2 Sensor Harness Connector (at sensor) — On the exhaust pipe, after the catalytic converter. Bank 1 is driver's side for V8s, passenger's side for V6s.. This is the primary point for visual inspection of melting/damage and for performing voltage and resistance tests on both the sensor and the harness side.
• PCM Connectors (e.g., C1, C2) — The Powertrain Control Module is typically located in the engine bay.. The O2 sensor signal, return, and heater control wires terminate at specific pins on these connectors. For example, on similar Chrysler platforms, the B2S2 signal and return are on C1 pins 33 and 32 respectively. Verifying continuity from the sensor connector to these pins is the definitive test for wiring integrity.
• G903 — This is a common ground point shown in wiring diagrams for related 3.6L engines.. Multiple sensors, including the O2 sensors, may share this ground point via a splice (e.g., S106). A loose or corroded G903 can cause erratic readings on all associated sensors, not just the B1S2 O2 sensor.

Real Owner Repair Stories

• Reddit user Galopigos in r/AskMechanics (General vehicle, but advice specific to P0138) — Persistent P0138 code that a mechanic could not figure out.
  ❌ Tried (didn't work) Initial diagnosis was inconclusive.
  ✅ What actually fixed it The user was advised that the harness had likely rubbed through and the sensor's heater voltage was shorting to the signal line. The recommended fix was to locate the melted/chafed section, cut out the damaged wires, and repair using solder seal or crimp-and-seal connectors, ensuring the harness is re-secured away from heat sources.

Model Year Variations Within This Range

• 2011-2023 (3.6L Pentastar V6): The 3.6L engine replaced the earlier 3.5L V6 in 2011. Wiring diagrams and component locations are specific to this engine. For example, a wiring diagram for the 3.6L shows a specific ground point G903 used by the O2 sensors.
• 2015-2023: The 2015 model year refresh included significant updates to the vehicle's electronics, including the Uconnect system and potentially PCM software logic. TSBs related to PCM software updates are often specific to post-2015 models.

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Hemi Tick (Lifter/Camshaft Failure) 🔴 High — Common across all Hemi engines (5.7L, 6.1L, 6.4L), particularly in 2009-2016 models, but can occur at any time. Often starts as a light tick and can progress to misfires and engine failure.
• Uconnect Screen Delamination 🟠 Medium — Very common on 2017 and newer models with the 8.4-inch screen. The screen bubbles and separates, causing 'ghost touches' and non-functionality. Typically occurs 1-3 years into ownership. (Ref: No recall, but subject of class-action investigation.)
• Active Exhaust Valve Squeak/Failure 🟡 Low — Common on R/T, Scat Pack, and Hellcat models 2015+. The butterfly valves in the exhaust tips begin to squeak loudly on startup or when opening/closing. Can eventually stick or fail.
• Alternator Failure 🟠 Medium — A frequent complaint across many model years, leading to battery drain and no-start conditions.
• Broken Exhaust Manifold Bolts 🟠 Medium — Common on 5.7L Hemi engines. The bolts, especially at the rear of the manifold, break and cause an exhaust leak, resulting in a ticking noise often mistaken for the 'Hemi Tick', especially when cold.
• Totally Integrated Power Module (TIPM) Failure 🔴 High → Shop Fuse Box — A known issue on 2008-2021 models, causing a wide range of bizarre electrical problems like random horn activation, starter issues, and fuel pump failure.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used part is a smart choice for a wiring harness pigtail. If the original connector body is melted or the locking tab is broken, splicing in a used pigtail from a salvage yard is a cost-effective and reliable repair.

Donor-vehicle mileage cap: roughly under 150000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For a wiring pigtail, inspect for any signs of brittleness, cracking, or heat damage on the plastic connector.
• Check that the connector pins are clean and free of corrosion.
• Ensure there is at least 4-6 inches of wire attached to allow for easy splicing.

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

• Oxygen Sensor

Aftermarket brands forum-validated for this vehicle:

• NTK (often the OEM supplier)
• Denso

Brands owners have reported issues with on this vehicle:

• Bosch (While a major OEM supplier for other brands, numerous forum posts across Chrysler/Dodge platforms report issues with aftermarket Bosch O2 sensors having slow response times or failing prematurely, with problems often being resolved by switching to NTK).

Real Owner Stories

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

Related OBD-II Codes

• P0158 — The Bank 2 equivalent of P0138; often appears simultaneously when wiring harnesses melt and short multiple sensor circuits together.
• P0172 — System Too Rich; a fuel system code that can cause the downstream O2 sensor to correctly read a high voltage due to excessive fuel.
• U140B — An electrical/communication code reported by owners alongside P0138, sometimes following battery replacement or engine work.
• B210D — A voltage-related code that has been observed by owners in conjunction with P0138 during electrical system failures.

Frequently Asked Questions