Failed heater element inside the downstream oxygen sensor (internal short to ground); Damaged, chafed or melted sensor wiring shorted to ground, often near the exhaust; Corroded or damaged connector or terminals at the sensor or in the harness; Blown fuse or faulty relay supplying the heater circuit, where fitted (depends on model); Fault in the heater driver within the engine control unit; Water ingress or contamination in the sensor connector causing a low reading.

P0037

HO2S Heater Control Circuit Low Bank 1 Sensor 2.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
0: AreaFuel and air metering, auxiliary emission controls
37: FaultThe specific fault in that area

What it means

P0037 means the control unit has detected a low voltage or low current condition in the heater control circuit of the downstream heated oxygen sensor (Bank 1, Sensor 2), which sits after the catalytic converter. The control unit drives the heater and monitors the circuit. If the circuit reads lower than expected, for example shorted to ground, the code is set.

Symptoms

Engine warning light on
Usually no noticeable change in driveability
Possible failed emissions test
Fuel economy may be slightly affected in some cases
Other oxygen sensor or catalyst monitor codes stored alongside it

Possible causes

Failed heater element inside the downstream oxygen sensor (internal short to ground)likely
Damaged, chafed or melted sensor wiring shorted to ground, often near the exhaustlikely
Corroded or damaged connector or terminals at the sensor or in the harnesspossible
Blown fuse or faulty relay supplying the heater circuit, where fitted (depends on model)possible
Fault in the heater driver within the engine control unitrare
Water ingress or contamination in the sensor connector causing a low readingrare

How to diagnose

Read all stored codes and freeze frame data, noting any other oxygen sensor or catalyst codes
Visually inspect the Bank 1 Sensor 2 wiring and connector for chafing, heat damage, corrosion and water ingress
Check the relevant fuse and relay for the heater supply, using the wiring diagram for the specific model and engine
Measure the heater element resistance at the sensor and compare it with the manufacturer's specification
Check the heater supply voltage and ground at the sensor connector with the ignition on
Check the control wire for a short to ground between the sensor connector and the control unit with the connector disconnected
View live data for the downstream sensor and confirm it warms up and switches as expected after repair
If wiring and sensor are good, have the control unit heater driver tested by someone with model-specific information

How to fix

Replace the Bank 1 Sensor 2 oxygen sensor if the heater element is shorted or out of specification
Repair or replace damaged wiring, securing it away from hot or sharp parts of the exhaust
Clean or replace corroded connector terminals and fix any water ingress
Replace the faulty fuse or relay after finding why it failed
Repair or replace the engine control unit only after all other causes are ruled out

Can I keep driving?

Low severity

The car is normally safe to drive for a short time, as this fault rarely affects driveability. Book it in soon, because a shorted circuit can blow a fuse and the fault may lead to an emissions test failure.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.