If your OBD-II scanner displays P0037, your vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected that the heater control circuit for the Bank 1 Sensor 2 heated oxygen sensor (HO2S) is operating below its expected voltage range.
The generic SAE definition for P0037 is:
HO2S Heater Control Circuit Low Bank 1 Sensor 2
Unlike P0036, which indicates a general heater circuit malfunction, P0037 specifically means the ECM has detected a low-voltage or excessive-current condition in the heater circuit for the downstream oxygen sensor.
Depending on the manufacturer, Bank 1 Sensor 2 may also be referred to as the:
- Downstream oxygen sensor
- Rear oxygen sensor
- Heated Oxygen Sensor (HO2S)
- Post-catalytic converter oxygen sensor
- Lambda sensor
- Rear lambda sensor
- Catalyst monitor oxygen sensor
- Heated exhaust oxygen sensor
The heater inside the oxygen sensor allows it to reach operating temperature much faster after startup. When the ECM detects abnormal electrical characteristics—such as excessive current draw or low circuit voltage—it stores diagnostic trouble code P0037.
Common causes include:
- Shorted oxygen sensor heater
- Short to ground
- Melted wiring
- Damaged connector
- Water intrusion
- Blown heater fuse (depending on design)
- Failed heater relay
- Chafed wiring harness
- Incorrect replacement sensor
- ECM driver failure
Although P0037 usually does not cause severe drivability problems, it can prevent emissions readiness monitors from completing and may cause your vehicle to fail an emissions inspection.
For additional troubleshooting information, browse our diagnostic libraries:
- Complete OBD-II Code Library: https://my.prostreetonline.com/dtc-obdii/
- Body (B) Code Library: https://my.prostreetonline.com/dtc-doctor/b-code-obd-ii-codes/
- Chassis (C) Code Library: https://my.prostreetonline.com/dtc-doctor/c-code-obd-ii-codes/
P0037 Quick Facts
| Item | Information |
|---|---|
| OBD-II Code | P0037 |
| Description | HO2S Heater Control Circuit Low Bank 1 Sensor 2 |
| Category | Powertrain |
| System | Heated Oxygen Sensor |
| Sensor | Bank 1 Sensor 2 |
| Location | Downstream (After Catalytic Converter) |
| Severity | Low to Moderate |
| Safe to Drive? | Usually Yes |
| Typical Repair Cost | $100–700+ |
What Does P0037 Mean?
P0037 indicates that the ECM has detected a low-voltage condition in the heater circuit of the downstream oxygen sensor located on Bank 1.
Most manufacturers interpret a “Circuit Low” condition as:
- Excessive current draw
- Short to ground
- Low-resistance heater element
- Internal heater short
- ECM driver overload
The ECM continuously monitors:
- Heater voltage
- Heater current
- Circuit resistance
- Driver feedback
If current exceeds calibrated limits or voltage falls below specifications, P0037 is stored.
What Is Bank 1 Sensor 2?
Understanding oxygen sensor locations makes diagnosing this code much easier.
Bank 1
Bank 1 is the side of the engine containing cylinder number one.
Inline engines have only Bank 1.
V6, V8 and flat engines typically have:
- Bank 1
- Bank 2
Sensor 2
Sensor 2 is always the downstream oxygen sensor.
It is installed:
- After the catalytic converter
- Behind the exhaust catalyst
- In the rear exhaust pipe
Unlike the upstream oxygen sensor, Sensor 2 primarily monitors catalytic converter efficiency rather than controlling fuel mixture.
What Does the Oxygen Sensor Heater Do?
The oxygen sensor contains an internal heating element that rapidly warms the sensing element after startup.
Benefits include:
- Faster catalyst monitoring
- Reduced emissions
- Quicker readiness monitor completion
- Improved cold-start emissions performance
Without the heater, the downstream sensor may require several minutes before it begins operating correctly.
Why Does the Downstream Sensor Have a Heater?
Although the downstream sensor doesn’t directly control air-fuel mixture, it must still reach operating temperature quickly to monitor catalytic converter efficiency.
The heater helps the ECM:
- Perform catalyst tests sooner
- Reduce cold-start emissions
- Complete emissions readiness monitors
- Verify catalytic converter performance
How the ECM Detects P0037
The ECM monitors:
- Heater voltage
- Heater current
- Circuit resistance
- Warm-up time
- Driver feedback
- Heater duty cycle
P0037 may be stored if:
- Circuit voltage remains too low
- Heater current is too high
- Heater resistance is too low
- Circuit shorts to ground
- Driver overload occurs
P0036 vs P0037 vs P0038
These three codes all diagnose the downstream oxygen sensor heater.
| Code | Description |
| P0036 | HO2S Heater Control Circuit Bank 1 Sensor 2 |
| P0037 | HO2S Heater Control Circuit Low Bank 1 Sensor 2 |
| P0038 | HO2S Heater Control Circuit High Bank 1 Sensor 2 |
Generally:
- P0036 = General circuit malfunction
- P0037 = Low voltage or excessive current
- P0038 = High voltage or insufficient current
Symptoms of P0037
Common symptoms include:
- Check Engine Light
- Failed emissions inspection
- Incomplete readiness monitors
- Increased cold-start emissions
- Delayed catalyst monitoring
- Slight reduction in fuel economy
Most drivers notice no change in engine performance.
Common Causes of P0037
1. Shorted Oxygen Sensor Heater
The heater element may internally short.
This is one of the most common causes.
2. Short to Ground
The heater wiring may contact:
- Exhaust pipe
- Catalytic converter
- Chassis
- Heat shield
Resulting in excessive current draw.
3. Melted Wiring
The downstream oxygen sensor is exposed to high exhaust temperatures.
Harness insulation may melt against:
- Exhaust pipe
- Catalytic converter
- Muffler
- Heat shields
4. Damaged Connector
Inspect for:
- Melted plastic
- Bent terminals
- Broken locking tabs
- Loose pins
5. Corroded Connector
Moisture intrusion may create:
- Green corrosion
- White oxidation
- Terminal bridging
6. Water Intrusion
Water entering the connector may short adjacent terminals together.
7. Incorrect Replacement Sensor
Incorrect sensors may have:
- Wrong heater resistance
- Incorrect current draw
- Incorrect connector
Always use a direct-fit OEM-quality replacement.
8. Blown Heater Fuse
Some vehicles share heater circuits among multiple oxygen sensors.
Always verify fuse condition using a multimeter.
9. Failed Heater Relay
Some manufacturers use a dedicated relay to power oxygen sensor heaters.
10. Damaged Wiring Harness
Inspect for:
- Chafed wiring
- Pinched harnesses
- Previous repairs
- Rodent damage
11. Poor Ground
Excessive ground resistance may affect heater operation.
Perform voltage-drop testing.
12. ECM Driver Failure
Although uncommon, the ECM’s internal heater driver may short internally.
Only suspect ECM failure after eliminating wiring faults.
Is P0037 Serious?
Generally Low to Moderate.
The vehicle usually remains completely driveable.
However, prolonged operation may result in:
- Failed emissions inspections
- Increased cold-start emissions
- Delayed catalyst monitoring
- Persistent Check Engine Light
Can You Drive With P0037?
Yes.
Most vehicles drive normally.
Repairs should still be completed before emissions testing.
How to Diagnose P0037
Step 1
Scan for additional codes.
Related codes include:
- P0030 – HO2S Heater Control Circuit Bank 1 Sensor 1
- P0031 – HO2S Heater Control Circuit Low Bank 1 Sensor 1
- P0032 – HO2S Heater Control Circuit High Bank 1 Sensor 1
- P0036 – HO2S Heater Control Circuit Bank 1 Sensor 2
- P0038 – HO2S Heater Control Circuit High Bank 1 Sensor 2
- P0136
- P0140
- P0141
- P0420
Step 2
Confirm Bank 1 Sensor 2 location.
Verify the sensor is installed after the catalytic converter.
Step 3
Inspect the connector.
Look for:
- Heat damage
- Corrosion
- Loose pins
- Melted housing
Step 4
Inspect the wiring harness.
Pay close attention to wiring routed near:
- Catalytic converter
- Exhaust pipe
- Heat shields
Step 5
Check the heater fuse.
Test electrically rather than visually.
Step 6
Measure heater resistance.
Low resistance typically indicates an internally shorted heater.
Step 7
Check for a short to ground.
Inspect both heater wires carefully.
Step 8
Verify power supply.
Confirm battery voltage reaches the heater connector.
Step 9
Perform voltage-drop testing.
Inspect:
- Grounds
- Power circuits
- Connectors
- Fuse terminals
Step 10
Command the heater using a bidirectional scan tool.
Monitor:
- Current draw
- Heater activation
- ECM response
Step 11
Check Technical Service Bulletins.
Some manufacturers have updated oxygen sensors or revised harness routing.
Step 12
Verify repair.
After repairs:
- Clear codes.
- Perform a cold start.
- Complete a drive cycle.
- Verify readiness monitors complete.
- Confirm P0037 does not return.
Common Repairs
| Repair | Estimated Cost |
| Heater fuse replacement | $10–50 |
| Wiring repair | $100–400 |
| Connector replacement | $75–250 |
| Downstream oxygen sensor replacement | $180–550 |
| Heater relay replacement | $80–200 |
| ECM programming | $100–300 |
| ECM replacement | $1,000–2,500 |
Common Diagnostic Mistakes
- Replacing the catalytic converter
- Replacing the upstream oxygen sensor
- Ignoring melted wiring
- Skipping resistance testing
- Not checking for shorts to ground
- Using incorrect replacement sensors
- Overlooking shared heater fuses
- Replacing the ECM prematurely
Vehicles Commonly Affected
P0037 may appear on virtually any OBD-II vehicle equipped with heated oxygen sensors, including:
- Acura
- Audi
- BMW
- Chevrolet
- Chrysler
- Dodge
- Ford
- GMC
- Honda
- Hyundai
- Infiniti
- Jeep
- Kia
- Lexus
- Mazda
- Mercedes-Benz
- Nissan
- Subaru
- Toyota
- Volkswagen
- Volvo
How to Prevent P0037
Reduce the likelihood of P0037 by:
- Inspecting oxygen sensor wiring during exhaust repairs
- Keeping wiring away from hot exhaust components
- Replacing damaged heat shields
- Repairing oil leaks promptly
- Using OEM-quality replacement oxygen sensors
- Repairing damaged connectors immediately
- Avoiding poor aftermarket wiring repairs
- Keeping moisture out of electrical connectors
Frequently Asked Questions
What does P0037 mean?
P0037 indicates the ECM has detected a low-voltage condition in the heater circuit for the Bank 1 Sensor 2 oxygen sensor.
Where is Bank 1 Sensor 2 located?
After the catalytic converter on the engine bank containing cylinder number one.
Can a bad oxygen sensor cause P0037?
Yes.
An internally shorted heater element is one of the most common causes.
Can wiring cause P0037?
Absolutely.
Heat-damaged wiring is frequently responsible.
Will P0037 affect engine performance?
Usually not.
Most vehicles drive normally.
Can I drive with P0037?
Yes.
However, emissions readiness monitors may not complete.
Will P0037 fail emissions?
Yes.
A Check Engine Light or incomplete readiness monitors generally cause an emissions inspection failure.
Will replacing the catalytic converter fix P0037?
No.
P0037 is an electrical heater circuit fault rather than a catalyst failure.
Final Thoughts
The P0037 code indicates the ECM has detected a low-voltage condition in the heater circuit for the downstream oxygen sensor (Bank 1 Sensor 2). The problem is most commonly caused by a shorted heater element, melted wiring near the exhaust, damaged connectors, or a short to ground.
Start diagnosis by confirming the correct oxygen sensor, inspecting the wiring around the catalytic converter, measuring heater resistance, and checking for shorts before replacing any components. In most cases, replacing the downstream oxygen sensor or repairing damaged wiring resolves the issue.
Related Articles
Continue diagnosing oxygen sensor and emissions-related faults with these guides already published on Pro Street:
Upstream Oxygen Sensor Heater Codes
- P0030 Code Explained: HO2S Heater Control Circuit Bank 1 Sensor 1
- P0031 Code Explained: HO2S Heater Control Circuit Low Bank 1 Sensor 1
- P0032 Code Explained: HO2S Heater Control Circuit High Bank 1 Sensor 1
Downstream Oxygen Sensor Heater Codes
- P0036 Code Explained: HO2S Heater Control Circuit Bank 1 Sensor 2
- P0038 Code Explained: HO2S Heater Control Circuit High Bank 1 Sensor 2
You can also browse the complete diagnostic libraries:
- Complete OBD-II Code Guide: https://my.prostreetonline.com/dtc-obdii/
- B Code OBD-II Library: https://my.prostreetonline.com/dtc-doctor/b-code-obd-ii-codes/
- C Code OBD-II Library: https://my.prostreetonline.com/dtc-doctor/c-code-obd-ii-codes/
