P0031 on 2013-2017 Honda Accord: Heater Circuit Causes and Fixes

What's Unique About the 2013-2017 Honda Accord

For the 9th generation Honda Accord, this is a straightforward and common fault. The key difference depends on your engine. On the 2.4L 4-cylinder (K24W1), 'Bank 1' is the only bank, and the sensor is easily accessible on the front exhaust manifold. On the 3.5L V6 (J35Y series), 'Bank 1' is the cylinder bank closer to the firewall, making that sensor more difficult to access than the Bank 2 sensor at the front of the car. Access may 🎬 Watch: Locate the Bank 1 sensor on your Accord require removing the engine cover and the front strut tower brace to reach it from above.

Symptoms You May Notice

• Check Engine Light is on
• Decreased fuel economy
• Rough or unstable idle, especially when the engine is cold
• Hesitation or sluggish acceleration
• Failing a vehicle emissions test
• Slightly stronger exhaust smell on startup

Most Likely Causes

1. Failed Bank 1, Sensor 1 (Air/Fuel Ratio Sensor) 🔴 High Probability The internal heating element of the sensor has a finite lifespan and is a common failure point due to constant, rapid heat cycles.
   How to confirm: Disconnect the sensor and measure the resistance between the two heater pins (usually the two same-colored wires, often black) using a multimeter. A healthy 🎬 See this guide on testing oxygen sensor heater circuits sensor should read between 1.8 and 3.4 ohms when cold. An open circuit (infinite resistance) or a reading far outside this range confirms the heater has failed.
   Typical fix: Replace the Bank 1, Sensor 1 Air/Fuel Ratio sensor. A 22mm or 7/8" offset oxygen sensor socket is recommended for removal. 🎬 Watch: Step-by-step walkthrough for replacing your oxygen sensors
   Est. part cost: $90-$280
2. Damaged Wiring or Connector 🟡 Medium Probability The wiring harness is close to hot exhaust components and can become brittle, melted, or corroded. Rodent damage is also a notable possibility, as the soy-based wire insulation used in this era can attract animals.
   How to confirm: Visually inspect the entire wiring harness leading to the sensor for any signs of melting, chafing, breaks, or chewing. Check the connector for corrosion or pushed-out pins. Use a multimeter to check for 12V power and a good ground at the harness-side connector with the key on, engine off.
   Typical fix: Repair the damaged section of the wiring harness or replace the connector pigtail. Honda sells anti-rodent tape (P/N 4019-2317) that can be wrapped around the new repair.
   Est. part cost: $10-$50
3. Blown Fuse ⚪ Low Probability
   How to confirm: Check the under-hood fuse box for the fuse labeled 'A/F HEATER'. On most 2013-2017 Accords, this is fuse A19, a 10A fuse. Refer to the owner's manual or fuse box diagram to confirm the location.
   Typical fix: Replace the blown fuse. If the fuse blows again immediately, it indicates a short circuit in the wiring or the sensor itself that must be found.
   Est. part cost: $1-$5

Rare But Worth Checking

• Faulty Powertrain Control Module (PCM): This is very uncommon. The PCM should only be considered after all other possibilities, including the sensor, wiring, and fuses, have been thoroughly tested and ruled out.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0031 is the primary code present.
2. Locate and check fuse A19 (10A) in the under-hood fuse box. Replace if blown. If it blows again, suspect a shorted sensor or wiring.
3. Visually inspect the Bank 1, Sensor 1 wiring harness and connector. Look for any obvious signs of damage, such as melting, fraying, rodent chew marks, or corrosion.
4. If the fuse and wiring look good, disconnect the sensor. Test for 12-volt power and ground on the vehicle's harness side of the connector (with the ignition on, engine off). Lack of power or ground points to a wiring issue upstream of the connector.
5. If power and ground are present, test the sensor itself. Measure the resistance across the two heater pins (typically same-colored wires) on the sensor. A reading outside the 1.8-3.4 ohm range indicates a bad sensor.
6. If the sensor and wiring test good, the fault may lie with the PCM, which is a rare occurrence.

Parts You'll Likely Need

• Air/Fuel Ratio Sensor (Bank 1, Sensor 1) (OEM #36531-5A2-A01 (for 2.4L engine) / 36531-RCA-A02 (for 3.5L V6 engine)) — This is the most common cause of a P0031 code, as the internal heater element fails over time. Denso is the Original Equipment Manufacturer (OEM) for Honda, so their aftermarket part is identical to the genuine Honda part.
  Trusted brands: Denso (OEM), NGK (NTK)
  OEM price range: $200-$280
  Aftermarket price range: $90-$150

Mechanic-Grade Diagnostic Values

• A/F Sensor Heater Circuit Current Draw — expected: Greater than 0.8 A when commanded on. Failure: Current is less than 0.8 A, triggering a P0031 fault.
• A/F Sensor Heater Power Supply Voltage — expected: 11V to 14V (Battery Voltage) with Key On, Engine Off. Failure: Voltage significantly below 11V indicates a wiring or fuse issue upstream of the sensor.
• Live Data - HO2S Heater Duty Cycle (Honda HDS) — expected: The PCM sends a pulse-width modulated (PWM) signal to control the heater. The duty cycle will vary based on conditions.. Failure: A 0% duty cycle when the heater should be on could indicate an ECM issue or a detected short/open that caused the ECM to shut down the circuit.

Scan Tool Commands That Help

• Honda HDS (or equivalent professional scanner): Live Data Monitoring: 'AF sensor (mA)', 'AF FB CMD', 'AF FB' — These parameters are used to assess the overall performance of the A/F sensor's sensing capability, not just the heater. While not a direct heater test, observing these values can help confirm if the sensor is completely unresponsive after a cold start, which would be consistent with a failed heater.
• OBD-II Scanner: Clear DTCs — After performing a repair (e.g., replacing the sensor or fixing wiring), clear the P0031 code. Then, perform a drive cycle to see if the code returns. A specific Honda drive cycle may be needed to get the oxygen sensor heater monitor to run and confirm the fix.

Wiring & Ground Locations

• G101 — Commonly found on the intake manifold plenum or thermostat housing area on the driver's side of the engine bay.. This is a primary ground termination point for the ECU and engine sensor harness. A corroded or loose G101 ground can cause a host of erratic sensor readings and codes, including P0031, due to improper voltage reference.
• A/F Sensor Connector (2.4L) — On the 2.4L K24W1 engine, the 4-pin connector for Bank 1 Sensor 1 is designated B7 in wiring diagrams.. This is the primary point for testing both the sensor-side resistance and the harness-side power/ground. Pin 1 (HA1A) is the heater control wire going to the ECM, and Pin 2 (+B) is the 12V power feed from the A/F Heater relay/fuse.
• ECM Connector (2.4L) — The heater control wire (HA1A) from the A/F sensor terminates at the B30 ECM connector, specifically at pin 109.. For advanced diagnostics where a wiring break is suspected between the sensor and the ECM, a continuity test can be performed between pin 1 of the B7 connector and pin 109 of the B30 ECM connector.

Real Owner Repair Stories

• driveaccord.net forum user (2013 Honda Accord Sport (2.4L)) — Check Engine Light with code P0031.
  ✅ What actually fixed it The user confirmed that replacing the Bank 1, Sensor 1 with a Denso 234-9131 aftermarket sensor resolved the code. They noted the dealer wanted over $500 for the repair, which they did themselves for the cost of the part.
• YouTube video by 'Car Garage' (Honda Pilot V6 (similar J-series engine architecture)) — Check Engine Light with codes P0134 and P2237 (related to B1S1).
  ✅ What actually fixed it The video demonstrates the replacement of the Bank 1, Sensor 1 on the firewall side of the V6 engine, confirming this location for 'Bank 1' and showing that replacement of the sensor fixed the codes.

OEM Part Supersession History

• 36531-5A2-A01 →
  Heads up: This part number appears to be consistent for the 2.4L engine across the entire 2013-2017 model range and even fits some later models and the CR-V. No significant supersessions or incompatibilities have been noted for this generation.

Model Year Variations Within This Range

• 2013-2017: The 2016 model year received a mid-cycle refresh which included updated styling and technology like Apple CarPlay/Android Auto. However, the core powertrain (K24W1 and J35Y series engines) and emissions components, including the A/F sensors related to P0031, were not changed. Diagnosis and repair remain identical across this entire year range.

Diagnostic Flowchart

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this specific repair, a used part is NOT recommended. The failure is due to the burnout of an internal heating element, which is a wear-and-tear item with a finite lifespan. A used sensor from a junkyard has unknown remaining life and is very likely to fail soon, if it works at all.

What to inspect on the donor part:

• Not applicable, as used parts are not advised.

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

• While not strictly 'OEM-only', it is critical to use a part from the Original Equipment Manufacturer. For Honda, this is typically Denso or NGK (sold as NTK). Avoid generic, no-name, or 'universal' sensors, as they often have incorrect heater resistance or response characteristics, leading to persistent codes.

Aftermarket brands forum-validated for this vehicle:

• Denso
• NGK / NTK

Brands owners have reported issues with on this vehicle:

• Generic 'universal' sensors
• Unbranded parts from online marketplaces

Real Owner Stories

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

Related OBD-II Codes

• P0032 — This is the direct counterpart to P0031, indicating the heater control circuit is HIGH instead of LOW. It points to the same component (Bank 1, Sensor 1) but suggests a short to power rather than an open circuit or short to ground.
• P0135 — A more generic code for 'O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)'. It shares the exact same root causes as P0031: a failed sensor heater, damaged wiring, or a blown fuse.
• P0134 — Indicates 'O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)'. A failed heater (the cause of P0031) will prevent the sensor from reaching operating temperature, which can lead to the PCM flagging it for inactivity.
• P0051 — This is the identical 'Heater Control Circuit Low' fault but for Bank 2, Sensor 1. It is highly relevant for V6 Accords, which have two banks and can experience the same sensor failure on the opposite side of the engine.
• P0171 — Indicates 'System Too Lean (Bank 1)'. A faulty Air/Fuel Ratio sensor, which is the component at fault for P0031, can send incorrect data to the engine computer, leading to improper fuel adjustments and triggering this fuel trim code.

Frequently Asked Questions