What Is P0037?
P0037 is an OBD-II diagnostic trouble code that indicates your vehicle’s engine control module (ECM) has detected a low voltage or low current condition in the heater control circuit for the downstream oxygen sensor (O2 sensor) on Bank 1, Sensor 2. This sensor is located after the catalytic converter on the side of the engine that contains cylinder #1.
The oxygen sensor heater is a critical component that warms the sensor to its optimal operating temperature quickly after engine start. When the heater circuit voltage drops below the manufacturer’s specification, the code is triggered. This prevents the oxygen sensor from functioning properly, which can affect fuel trim calculations and emissions control.
What Does P0037 Mean?
Bank 1 refers to the side of the engine containing the #1 cylinder. Sensor 2HO2S (Heated Oxygen Sensor) heater control circuit is the electrical circuit that powers the heating element inside the sensor.
When the ECM commands the heater on, it expects to see a specific voltage and current draw. If the voltage drops too low or the current is insufficient, the module detects this abnormal condition and sets code P0037. This could mean:
- The heater element inside the sensor has failed or is failing
- There’s a break or high resistance in the wiring harness
- A connector is corroded or loose
- The heater control relay or fuse is faulty
- The ECM’s heater control circuit is malfunctioning
Common Symptoms
- Check Engine Light (CEL) illuminated on the dashboard
- Poor fuel economy – the vehicle may run rich due to incorrect oxygen sensor feedback
- Rough idle or hesitation during acceleration
- Failed emissions test – increased emissions due to improper fuel mixture
- Difficulty starting in cold weather (heater not warming sensor quickly)
- Engine running lean or rich – noticeable performance issues
- In many cases, no drivability symptoms – the code may be the only indicator
Possible Causes (Ranked by Frequency)
1. Faulty Oxygen Sensor (Most Common)
The internal heater element has burned out or is failing. This is the most common cause of P0037. Oxygen sensors typically last 80,000–100,000 miles before the heater element degrades.
2. Wiring Harness Issues
Corroded, damaged, or pinched wiring between the sensor and the ECM creates high resistance or an open circuit. Road salt, moisture, and heat can degrade wiring over time.
3. Loose or Corroded Connector
The oxygen sensor connector may be loose, corroded, or improperly seated, preventing proper electrical contact and voltage delivery to the heater.
4. Faulty Heater Relay or Fuse
The relay controlling the heater circuit or the fuse protecting it may have failed, cutting power to the heater element.
5. Engine Control Module (ECM) Fault
In rare cases, the ECM’s heater control circuit or driver has failed, preventing it from supplying adequate voltage to the sensor heater. This is uncommon but possible.
6. Ground Connection Issues
A poor ground connection between the sensor, wiring, and the vehicle chassis increases resistance and reduces heater current draw.
Diagnostic Steps
Step 1: Read the Full Diagnostic Trouble Code
Use an OBD-II scanner to confirm code P0037 and check for any related codes (such as P0036, P0038, P0039) that might indicate a broader issue.
Step 2: Visually Inspect the Oxygen Sensor and Wiring
Locate the Bank 1 Sensor 2 (downstream sensor on the exhaust manifold side with cylinder #1). Inspect the sensor connector and wiring harness for:
- Corrosion or white/green oxidation on connector pins
- Damaged, pinched, or melted wiring insulation
- Loose or partially disconnected connectors
- Water intrusion or moisture in the connector
Step 3: Check the Heater Fuse and Relay
Consult your vehicle’s service manual to locate the oxygen sensor heater fuse and relay. Inspect the fuse for a blown element. Use a multimeter to test the relay for proper operation.
Step 4: Test Heater Circuit Voltage
With the engine off, disconnect the oxygen sensor connector. Set a multimeter to DC voltage mode and probe the heater circuit wires (typically the black and white or black and gray wires, depending on the vehicle). Key on, engine off (KOEO), you should see 12V between the heater positive and ground.
If voltage is low or absent, the issue is in the wiring, relay, fuse, or ECM. If voltage is present, the problem is likely the sensor heater element itself.
Step 5: Measure Heater Resistance
With the sensor disconnected, use a multimeter set to resistance (ohms) mode to measure the heater element’s resistance. A typical oxygen sensor heater should read between 2–14 ohms, depending on the manufacturer. An open circuit (infinite resistance) or very low resistance indicates a faulty sensor.
Step 6: Inspect Connectors and Clean if Necessary
Disconnect the oxygen sensor connector and inspect the pins. If corrosion is present, carefully clean the pins with electrical contact cleaner and a small brush. Reconnect and retest.
Step 7: Clear the Code and Test Drive
After repairs, clear the code using your scanner and take the vehicle for a 15–20 minute test drive to allow the oxygen sensor to reach operating temperature. Monitor for code recurrence.
Repair Cost Estimates
Oxygen Sensor Replacement
- Parts Cost: $40–$200 depending on the vehicle make/model and sensor quality
- Labor Cost: $75–$300 (typically 0.5–1.5 hours)
- Total: $115–$500
Wiring Harness Repair or Replacement
- Parts Cost: $50–$150
- Labor Cost: $100–$400
- Total: $150–$550
Connector Repair or Replacement
- Parts Cost: $10–$50
- Labor Cost: $50–$150
- Total: $60–$200
Fuse or Relay Replacement
- Parts Cost: $5–$30
- Labor Cost: $0–$100 (often DIY)
- Total: $5–$130
ECM Repair or Replacement (Rare)
- Parts Cost: $300–$1,500
- Labor Cost: $200–$800
- Total: $500–$2,300
Can I Still Drive With P0037?
Severity: Moderate. You can typically drive with P0037, but it’s not recommended for extended periods.
Safety: P0037 does not pose an immediate safety risk. The vehicle will not stall or lose power. However, the downstream oxygen sensor heater not functioning properly means the sensor takes longer to reach operating temperature, which affects fuel trim calculations and emissions control.
Drivability: In most cases, you won’t notice significant performance issues, though fuel economy may suffer slightly and the engine may run slightly rich or lean. Some vehicles may experience rough idle or hesitation, especially in cold weather.
Emissions: The vehicle may fail an emissions test due to increased NOx, CO, or HC emissions caused by improper fuel mixture feedback.
Recommendation: Repair the issue within a few weeks. Don’t ignore it for months, as continued operation with a faulty oxygen sensor can eventually damage the catalytic converter, leading to much more expensive repairs ($800–$2,000+).
Frequently Asked Questions
Q: What’s the difference between Bank 1 Sensor 1 and Bank 1 Sensor 2?
A: Sensor 1 (upstream) is located before the catalytic converter and measures oxygen content to help the ECM adjust fuel mixture in real-time. Sensor 2 (downstream) is located after the catalytic converter and monitors converter efficiency. P0037 affects Sensor 2, which is less critical for engine performance but important for emissions control.
Q: Can I drive with a bad oxygen sensor heater?
A: Yes, you can drive, but the sensor won’t heat up quickly, especially in cold weather. This causes delayed feedback to the ECM, potentially leading to poor fuel economy and rough running. It’s best to repair it within a few weeks to avoid catalytic converter damage.
Q: Is P0037 the same as P0036?
A: No. P0036 is “HO2S Heater Control Circuit High Bank 1 Sensor 2,” indicating excessive voltage or current. P0037 is “Low,” indicating insufficient voltage or current. Both point to heater circuit problems but suggest different root causes.
Q: How much does it cost to fix P0037?
A: Most commonly, replacing the oxygen sensor costs $115–$500 depending on your vehicle. Wiring or connector repairs may cost $60–$550. Always get a diagnosis before paying for repairs, as the exact cost depends on the root cause.
Q: Can I replace the oxygen sensor myself?
A: Yes, if you have basic mechanical skills and tools. The sensor is typically accessible and requires only a socket wrench and an oxygen sensor socket. However, the sensor may be tight and hot, so caution is needed. Consult your vehicle’s service manual for specific instructions.