Emissions

P0037 — Downstream O2 Sensor Heater Control Circuit Low (Bank 1 Sensor 2)

Severity: low Safe to drive

What P0037 means

The PCM switches the heater in the bank 1 downstream (post-catalyst) oxygen sensor and monitors the circuit voltage. The heater brings the sensor up to operating temperature quickly and keeps it there when the exhaust is cool. P0037 sets when the control circuit reads lower than expected, which points to a shorted-to-ground wire, a failed heater element, a wiring fault, or rarely a PCM driver problem.

Symptoms

  • Check engine light on
  • Failed emissions test
  • Slightly worse fuel economy
  • Occasional unstable idle
  • Often no other noticeable symptoms

Possible causes

  1. Failed heater element in the bank 1 downstream O2 sensor
  2. Damaged wiring or connector in the heater circuit
  3. Heater control wire shorted to ground
  4. Poor or corroded ground connection
  5. Blown fuse or faulty heater relay
  6. Failed heater driver inside the PCM (rare)

How to diagnose

  1. Scan for codes and freeze frame data, and note any other O2 sensor codes
  2. Inspect the bank 1 sensor 2 wiring and connector for chafing, heat damage and corrosion
  3. Check the heater fuse and relay using the vehicle wiring diagram
  4. Measure the heater resistance at the sensor terminals and compare it with spec
  5. Check for power and a control signal at the harness connector with the key on
  6. Test the control wire for a short to ground and for an open circuit
  7. Look for exhaust leaks near the sensor
  8. If the wiring and sensor are good, test the PCM heater driver

Common fixes

  • Replace the bank 1 downstream O2 sensor
  • Repair the wiring or connector
  • Replace the blown fuse or faulty relay
  • Restore the ground connection
  • Repair or replace the PCM as a last resort

Questions and answers

Can I drive with a P0037 code?

Usually yes, because it rarely affects engine performance. Still, fix it soon to keep emissions in check and to pass inspection.

What most often causes P0037?

A failed heater inside the sensor or damaged wiring is the most common cause. Start by inspecting the connector and measuring the heater resistance.

Should I replace the sensor right away?

No. Check the fuse, wiring and ground first, because a harness short to ground sets the same code and a new sensor won't fix it.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.