OBD-II Code · Sensors
P0037
HO2S Heater Control Circuit Low (Bank 1 Sensor 2)
Severity
low
Lowest on our scale. Fix it when convenient.
Can you drive it
Only if running normally
A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety.
Indicative cost (USD)
$150–$400
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
Downstream O2 heater circuit reading low on bank 1.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
- Possible emissions failure
Likely causes
- Failed downstream O2 sensor heaterMost common
- Short to ground in wiring
- Blown fuse
Read the full diagnostic procedureP0037 means the downstream Bank 1 heater control circuit is pulled low — either the heater is internally shorted, the harness is grounded, or the PCM…
P0037 means the downstream Bank 1 heater control circuit is pulled low — either the heater is internally shorted, the harness is grounded, or the PCM driver is shorted on.
Cheapest test
disconnect the sensor, ohm pin-to-pin on the heater — narrowband downstream should read 2-10 ohms cold (Denso Toyota units run 11-14 ohms). Below 1 ohm indicates a shorted element. With the sensor unplugged, key-on, the harness-side control pin should float at battery voltage; if it reads zero, the harness is shorted to ground between connector and PCM. Verify the heater fuse and check for melted insulation routing past the catalyst heat shield. Scope ground-side PWM — pinned at 100% duty with collapsed voltage confirms a hard short. Heater current draw above 3A with the sensor connected means an internal short pulling excessive current — replace the sensor before it damages the PCM driver. Expensive misdiagnosis: replacing the PCM for a 'failed driver' when the real fault is a chafed harness shorting the control wire to chassis ground; always isolate the harness before module replacement.
Vehicle-specific patternsGM 5.3L/6.0L trucks (2003-2014) melt the downstream harness onto the cat heat shield, shorting the heater control to ground.
- 2003-2014GM 5.3L/6.0L trucks melt the downstream harness onto the cat heat shield, shorting the heater control to ground. Toyota 2GR-FE (Camry/Avalon/Sienna 2007-2012) downstream Denso sensors short internally on the heater element with age. Ford 4.6L/5.4L Modular (Crown Vic/F-150/Expedition 2004-2010) commonly shorts the downstream heater wire where the harness passes the transmission bellhousing bracket. Subaru EJ25 (Outback/Forester 2005-2012) sees downstream sensor internal shorts after extended rich-running events from a failing upstream sensor.
Estimated repair$120 to $380.
Look up another code
P0037 — frequently asked
What does a P0037 code mean?
Downstream O2 heater circuit reading low on bank 1.
What causes a P0037 code?
Common causes: Failed downstream O2 sensor heater; Short to ground in wiring; Blown fuse.
What are the symptoms of a P0037 code?
Typical symptoms: Check engine light; Possible emissions failure.
Is it safe to drive with a P0037 code?
Only if running normally. A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety. Estimated repair: $150-$400.
How do I diagnose a P0037 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
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