P0037
HO2S Heater Control Circuit Low (Bank 1 Sensor 2)P0037 is a generic OBD-II powertrain diagnostic trouble code: HO2S Heater Control Circuit Low (Bank 1 Sensor 2). It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0037 means
P0037 is set when the PCM detects that the heater control circuit for Bank 1, Sensor 2 — the downstream (post-catalyst) oxygen sensor on the cylinder-1 side of the engine — is operating below its expected voltage or current threshold. Unlike the upstream Sensor 1 which drives fuel trim, Sensor 2's primary role is catalytic converter efficiency monitoring: the PCM compares Sensor 2's relatively stable output to Sensor 1's switching signal to evaluate whether the converter is functioning correctly.
A "Low" circuit condition on this downstream heater circuit typically indicates an open wire, a short to ground, a blown fuse, or a failed internal heater element. The PCM controls the heater via a ground-side driver or a controlled voltage feed and monitors the resulting circuit state; when the measured value stays below the calibrated minimum, the fault counter increments and P0037 is stored.
Because Sensor 2 is passive to fuel delivery, this fault rarely causes noticeable drivability symptoms. However, the MIL will illuminate and any downstream catalyst-efficiency monitor (P0420/P0430) may also be affected or suppressed while the heater fault is present. The vehicle remains driveable in most cases.
Common causes
Most-frequently reported root causes when P0037 is logged.
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1
Failed internal heater element inside the Bank 1 Sensor 2 downstream oxygen sensor (most common).
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2
Open circuit or broken wire in the heater supply or ground/control leg of the downstream sensor harness.
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3
Short to chassis ground on the heater control wire, dropping circuit voltage below the minimum threshold.
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4
Corroded, backed-out, or moisture-contaminated connector at the sensor or harness junction.
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5
Blown fuse in the downstream sensor heater supply circuit.
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6
Loose or corroded chassis ground strap adding resistance to the heater return path.
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7
PCM heater output driver degradation preventing sufficient drive to the heater circuit.
Symptoms drivers notice
How to diagnose P0037
A typical diagnostic flow when this code is present.
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1
Connect a scan tool, read all stored DTCs, and note freeze-frame data; check whether any catalyst-efficiency code (P0420) is stored alongside P0037.
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2
Visually inspect the Bank 1 Sensor 2 harness from the sensor — located after the catalytic converter — to the PCM connector, paying attention to heat damage near the catalyst or physical damage underneath the vehicle.
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3
Check the relevant heater circuit fuse against the fuse-box diagram and replace any blown fuse, then identify the root cause before condemning the sensor.
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4
With the sensor disconnected and ignition on / engine off, use a multimeter to confirm 12 V is present on the heater supply pin at the harness-side connector.
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5
Measure continuity and resistance on the heater ground/control return wire back to the PCM; excessive resistance or an open indicates a harness fault.
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6
Measure heater element resistance directly between the heater pins at the sensor (typically 4–30 Ω; infinite resistance confirms an open element).
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7
If all circuits test good, replace the Bank 1 Sensor 2 oxygen sensor with an OEM or quality equivalent, clear codes, and verify the heater monitor completes on the next drive cycle.
Related powertrain codes
Frequently asked questions
What does Bank 1, Sensor 2 do?
Bank 1 Sensor 2 is the downstream (post-catalyst) oxygen sensor on the cylinder-1 side of the engine. Its primary function is to help the PCM assess catalytic converter efficiency by comparing its output to the upstream Sensor 1 signal. It does not directly influence fuel trim.
Will P0037 cause a P0420 catalyst fault?
It can. While the downstream heater is inoperative, the PCM may be unable to run the catalyst monitor, so a P0420 could be suppressed or could set independently if the converter was already struggling. Fix P0037 first, then re-evaluate for P0420.
Is P0037 more or less serious than P0031?
P0037 is generally less urgent for drivability, because the downstream sensor does not drive fuel delivery. However, both codes illuminate the MIL and both indicate a fault that needs repair to keep emission monitoring functional.
Can exhaust heat cause P0037?
Yes. The downstream sensor is mounted near or behind the catalytic converter, which runs very hot. Wiring routed too close to the converter body can have its insulation melted, causing a short to ground or an open circuit that triggers P0037.
Disabling P0037 in software
RaceTune can permanently disable P0037 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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