P0037 Code: O2 Sensor Heater Control Circuit Low (Bank 1 Sensor 2)
No current flows through the heater of the sensor behind the bank 1 converter – open element or wiring.
At a glance
Severity: Minor
- Meaning
- O2 Sensor Heater Control Circuit Low (Bank 1 Sensor 2)
- System
- Fuel & Air Metering · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $0–$320
- DIY difficulty
- Easy
With P0037 the engine computer is reporting that the heater of the downstream oxygen sensor on bank 1 draws no current when commanded on, as if the circuit were broken. This sensor threads into the exhaust just behind the catalytic converter and hangs in the airstream under the car, so it lives through harsh temperature swings: a hot sensor hit by a splash of cold water can crack its ceramic heater, which then measures open. The other big source of P0037 is recent work near the exhaust. Converter replacement, muffler or hanger repairs, transmission removal or a lift pad placed in the wrong spot can leave the sensor unplugged, the pigtail torn or the connector hanging loose.
Can I keep driving? Safe to drive; fueling isn't noticeably affected. If the code appeared right after exhaust work, check it soon, because a dangling connector can get ripped off completely.
How to read P0037
- P Powertrain
- 0 Generic (SAE)
- 0 Fuel/air & emissions (aux.)
- 37 Specific fault
Symptoms
- Check engine light shortly after start-up on nearly every trip
- Code appeared right after converter, muffler or transmission work
- Downstream sensor data very slow to respond on short, cool trips
- Catalyst monitor stuck at incomplete
- Blown heater fuse with upstream heater codes logged as well
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Heater element open, often cracked by cold water hitting the hot sensor
- Connector left unplugged or pigtail torn during exhaust, converter or transmission work
- Shared heater fuse blown
- Feed or control wire broken where the harness crosses the transmission or floor pan
- Heater driver in the engine computer failed open
- Corroded terminal pushed back in the connector so it no longer makes contact
Diagnosis step by step
Check the obvious after recent work
Raise the car safely and follow the pigtail from the sensor to its connector. Is it plugged in, latched and clipped in place? Look closely at where the wires enter the connector body; a pigtail that was stretched when the exhaust was lowered often breaks right there.
Tools: Flashlight
Ohm-test the heater on the sensor side
Unplug the connector and measure across the two heater wires of the sensor (usually the two wires of the same color). A narrowband heater typically shows about 3 to 20 ohms depending on make. OL confirms an open element.
Tools: Multimeter
Load-test feed and control with a test light
A meter can show 12 volts on a wire that can't carry current. With the sensor unplugged and key on, a test light from the feed pin to ground should light brightly. Then connect it between the feed and control pins with the engine idling: it should glow or pulse when the computer commands the heater.
Tools: Multimeter
Check which heaters share the fuse
Look up the fuse that feeds this heater; it often also supplies the upstream sensor and sometimes the injectors or coils. If it's blown, P0037 is only the messenger; something else shorted it, and a heater code 'high' or a rubbed wire is the next place to look.
Tools: Multimeter
Remove the old sensor carefully
Downstream sensors are often seized. Run the engine briefly to warm the exhaust, use penetrating oil and a proper O2 sensor socket, and clean the threads in the exhaust with an M18 x 1.5 thread chaser before fitting the new one. Put anti-seize only on the threads, never on the tip.
Tools: O2 sensor socket, Torque wrench
Clear and verify
Clear the code, start the engine and check that the heater status reads on and the sensor starts switching after warm-up. Then complete a drive with steady cruising so the catalyst monitor can finish.
Tools: OBD-II scanner
Where the parts are
- 1Upstream O2 sensor
- 2Catalytic converter
- 3Downstream O2 sensor
- 4Diesel particulate filter
- 5Turbocharger
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Reconnect and clip the sensor connector | Yes | $0–$20 |
| Downstream O2 sensor, part only | Yes | $40–$140 |
| Downstream sensor replaced at a shop, including seized removal | No | $140–$320 |
| Splice a torn pigtail with heat-rated repair wire | No | $70–$200 |
| Repair damaged sensor threads in the exhaust | No | $50–$200 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
With P0037 stored the check engine light is on and an OBD-II smog check fails. Clearing the code the morning of the test won't help either, because the catalyst and heater monitors will show not ready.
Frequently asked questions
P0037 started right after I had a new catalytic converter fitted. Why?
The downstream sensor has to be removed or disconnected for that job. It's common for the connector to be left unlatched, for the pigtail to be stretched, or for the old sensor's heater to crack while being removed. Have the shop check the connection and the heater resistance.
Can a splash of cold water really kill the heater?
Yes. The heater is a ceramic element running at several hundred degrees, and a sudden quench from a deep puddle or snowmelt can crack it. That's why downstream sensors on cars driven in wet, salty conditions fail more often than you'd expect.
Can I use an upstream sensor in the downstream position?
Usually not. On many modern cars the upstream sensor is a wideband type with a different connector, and even when both are narrowband they often differ in cable length and heater rating. Order the part listed for the downstream position.
Why does a test light find problems a multimeter misses?
A meter draws almost no current, so a wire hanging on by a single strand can still show full voltage. A test light draws real current and dims or goes out on a weak connection, which is closer to how the heater loads the circuit.