P0037 on 2021 Chrysler Pacifica: O2 Sensor Heater Circuit Low Causes and Fixes

What's Unique About the 2021-2021 Chrysler PACIFICA

For the 2021 Chrysler Pacifica with the 3.6L V6 engine, Bank 1 is the cylinder bank closer to the firewall. The Sensor 2 O2 sensor is positioned downstream of the catalytic converter on that bank. While the fault is common across many vehicles, Chrysler issued a Technical Service Bulletin (TSB #18-050-22 REV A) that groups P0037 with several other O2 sensor heater circuit codes. This TSB involves a Powertrain Control Module (PCM) software update to correct false or intermittent fault detections, making a dealer visit or use of a capable scan tool to check for software updates a critical first diagnostic step before replacing parts.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Check Engine Light is on
• Failing an emissions test
• Slightly reduced fuel economy
• Rough or uneven idling in some cases

Most Likely Causes

1. Failed Bank 1, Sensor 2 Oxygen Sensor 🔴 High Probability The internal heater element within the O2 sensor is a common failure point due to constant heat cycles and exposure to exhaust gases, typically failing after 70,000-100,000 miles. For Chrysler products, using OEM-equivalent brands like NTK is highly recommended to avoid compatibility issues.
   How to confirm: Disconnect the sensor and measure the resistance across the two heater circuit pins (usually the two same-colored wires) with a multimeter. A reading outside the typical range of 3-25 Ohms or an open circuit (infinite resistance) confirms a failed heater element. A good sensor will often read between 4 and 10 ohms when cold.
   Typical fix: Replace the Bank 1, Sensor 2 oxygen sensor. Use a 22mm O2 sensor socket for removal and apply anti-seize compound to the threads of the new sensor before installation.
   Est. part cost: $50-$150
2. Outdated Powertrain Control Module (PCM) Software 🟡 Medium Probability Chrysler released TSB 18-050-22 REV A specifically for 2021 Pacifica models, which indicates that the PCM may be too sensitive and can set various O2 heater codes, including P0037, erroneously.
   How to confirm: A dealership or a repair shop with a wiTECH scan tool can check the current PCM software calibration ID against the latest version available from Chrysler. If an update is available, it should be performed.
   Typical fix: Reprogram the PCM with the latest software calibration. This is often done before any parts are replaced, as it may resolve the code on its own.
   Est. part cost: $0 (if under warranty) - $200
3. Damaged Wiring or Connector 🟡 Medium Probability The sensor and its wiring are located under the vehicle, making them susceptible to damage from road debris, moisture, and high exhaust temperatures which can melt, corrode, or fray the wiring.
   How to confirm: Visually inspect the entire wiring harness from the sensor to the main connector for any signs of melting, chafing, corrosion, or loose pins. Perform a voltage test at the harness-side connector (with sensor disconnected and ignition on) to ensure it's receiving power (around 12V) and has a good ground.
   Typical fix: Repair the damaged section of the wire or replace the connector pigtail. Use heat-shrink tubing to protect the repair.
   Est. part cost: $10-$40
4. Blown Fuse ⚪ Low Probability
   How to confirm: Locate the fuse for the O2 sensor heater circuit in the vehicle's fuse box (consult the owner's manual for the specific location, often labeled 'O2 HTR' or similar). Visually inspect the fuse or test it for continuity with a multimeter.
   Typical fix: Replace the blown fuse. If it blows again, a short circuit in the wiring or the sensor's heater element is present and must be found.
   Est. part cost: $1-$5

Rare But Worth Checking

• Faulty Powertrain Control Module (PCM): This is extremely rare. The PCM's internal driver for the heater circuit can fail, but all other possibilities (software, sensor, wiring, fuse) should be exhaustively ruled out before considering PCM replacement. Sometimes a persistent code after replacing the sensor can point to a PCM issue, as noted by some owners in forums.

Diagnosis Steps

1. Verify the code P0037 is present using an OBD-II scanner. Note any other codes present.
2. Check for applicable TSBs. For a 2021 Pacifica, TSB 18-050-22 REV A is highly relevant. Check if the PCM software update has been performed before proceeding.
3. Visually inspect the Bank 1, Sensor 2 oxygen sensor (located after the catalytic converter on the firewall side of the engine) and its wiring harness. Look for any signs of melting, chafing, corrosion, or disconnection.
4. Locate and check the fuse for the O2 sensor heater circuit (typically 10-15A). Replace if blown.
5. If the fuse and wiring appear intact, disconnect the sensor's electrical connector.
6. With the ignition on (engine off), use a multimeter to check for battery voltage (approx. 12V, may be higher if charging) on the power supply wire of the harness-side connector.
7. Check for a good ground on the ground wire of the harness-side connector. On many Chrysler systems, the PCM provides a duty-cycled ground to control the heater, so a simple continuity-to-ground test with the key off may not be sufficient.
8. Using the multimeter set to Ohms, measure the resistance between the two heater pins on the sensor itself. A typical reading is between 3 and 25 ohms when cold. An infinite reading (open) or zero reading (short) indicates a bad sensor.
9. If wiring, fuse, and sensor resistance are all good, and the PCM software is up to date, the problem may lie with the PCM, which requires professional diagnosis.

Parts You'll Likely Need

• Oxygen Sensor (Bank 1, Sensor 2) (OEM #5149180AA) — The internal heater element is the most common point of failure for this code.
  Trusted brands: NTK (NGK), Denso, Bosch
  OEM price range: $115-$180
  Aftermarket price range: $50-$110

Related Codes That Often Appear With This One

• P0137 — This code indicates low voltage from the sensor signal circuit (Bank 1, Sensor 2), which may be logged if the sensor is not heating up and functioning correctly.
🎬 See this guide on troubleshooting related Chrysler O2 sensor circuit codes.
• P0038 — This is the opposite code, indicating a 'Heater Circuit High' condition. Seeing both intermittently could point to a severe wiring short or a PCM driver fault.
• P0141 — This is a more general code for 'O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)'. P0037 is the more specific 'low voltage' version of this fault.

Technical Service Bulletins (TSBs) & Recalls

• 18-050-22 REV A - This bulletin involves updating the Powertrain Control Module (PCM) with the latest software to address a condition where a Malfunction Indicator Lamp (MIL) is illuminated and DTCs P0037, P0031, P0032, P0038, and others may be set. This applies specifically to 2021 Chrysler Pacifica models.

Platform-Specific Known Issues

• Mandatory PCM Software Check (TSB 18-050-22 REV A): Before replacing any hardware for a P0037 code on a 2021 Pacifica, it is critical to check if the PCM has the latest software. TSB 18-050-22 REV A was released to address this and a host of other O2 sensor heater codes that could be set erroneously. The fix is a simple software reflash performed by a dealer or qualified shop.

Mechanic-Grade Diagnostic Values

• O2 Sensor Heater Element Resistance — expected: Between 3 and 25 Ohms when the sensor is at ambient temperature. Many healthy sensors for Chrysler vehicles measure between 4-10 Ohms.. Failure: A reading of infinite resistance (Open Loop, 'OL') or zero resistance (a dead short) indicates a failed heater element.
• Heater Circuit Power Supply Voltage — expected: Approximately battery voltage (12.0-12.6V) with Key On, Engine Off (KOEO). May read higher (13.5-14.5V) with the engine running due to alternator output.. Failure: A reading near 0V indicates an open circuit or blown fuse on the power supply side.
• Heater Circuit Ground Control Signal — expected: Using an oscilloscope, a square wave (duty cycle) should be visible when the PCM is commanding the heater on (typically on cold start). Using a multimeter, the voltage may appear as an average that is neither 0V nor battery voltage.. Failure: A constant 12V on the ground control wire indicates an open in the ground circuit or a failed PCM driver. A constant 0V (ground) could indicate a short to ground in the wiring.

Scan Tool Commands That Help

• wiTECH: O2 Heater Actuation Test / System Test — This function, found in the dealer-level scan tool, allows a technician to command the O2 sensor heater circuit on and off manually. This is used to verify that the PCM driver, wiring, and fuse are all capable of delivering power and ground to the sensor, helping to isolate the fault to the sensor itself if the circuit tests good.

Wiring & Ground Locations

• B1S2 Heater Wires — On the oxygen sensor's 4-wire connector.. The heater circuit wires are almost always the two wires of the same color (e.g., two black wires or two white wires). The other two mismatched-color wires are for the sensor signal and signal ground. Correctly identifying the heater wires is critical for performing resistance and voltage tests.
• Harness Routing — The wiring harness for the rear oxygen sensor runs along the transmission and chassis, near the exhaust.. This area is prone to damage. The harness can rub against the transmission case, driveshaft (on AWD models), or chassis components, eventually chafing through the insulation and causing a short or open circuit that triggers P0037.

Real Owner Repair Stories

• General automotive repair knowledge, illustrated by a user with a GM vehicle. (2009 Chevrolet Suburban (illustrative example)) — Persistent heater circuit codes and poor running conditions.
  ❌ Tried (didn't work) Initial diagnosis pointed towards a bad sensor.
  ✅ What actually fixed it A thorough inspection of the wiring harness revealed that it was rubbing against the transmission and driveshaft area, exposing the copper wires. Repairing the chafed wires and securing the harness away from the moving parts resolved the issue without needing to replace the sensor.

OEM Part Supersession History

• 5149180AA → 5149180AB — Unconfirmed by manufacturer, but part supersessions are typically made to improve durability, resolve a known issue, or switch suppliers. It may involve a more robust internal heater element or improved connector seals.
  Heads up: The new part number 5149180AB is a direct replacement for 5149180AA and is fully compatible.