Error Code P0038 is defined as HO2S (Heated Oxygen Sensor) Heater Control Circuit High Bank 1, Sensor 2. It’s a generic definition which usually means there’s a problem with the heater element circuit of the HO2S.

Different manufacturers may have different definitions and information about this error code, thus, it is important to know the specified information for the make and model of the vehicle.

Definition

Today’s engines come with oxygen sensors with heating elements (HO2S). The PCM (powertrain control module) uses the information from the HO2S to determine the oxygen level of the engine’s exhaust system. Bank 1 sensor 2 is located at the back of bank 1. The PCM uses the data from the HO2S mainly to monitor the catalytic converter’s efficiency, which is an extremely important component of the heater element.

The PCM sets the operating temperature of the engine by controlling the heater to warm it up. This is what allows the engine to enter its closed loop more efficiently, as well as emissions on a cold startup. The PCM will constantly monitor the circuit for any abnormal changes in the voltage, or even amperages (in some cases). Depending on the make of the vehicle, the O2 sensor heater is controlled by the PCM in one of two ways: the first way is that the PCM is able to directly control the voltage to the heater, either directly or via HO2S relay, while the common ground of the vehicle supplies the ground. Second way is that, a fused 12V battery feed (B+) which feeds 12V to the heater element at any time the ignition is on. The control for the

The PCM detects this error code when it sees an excessively high voltage through the HO2S.

Common Symptoms

Though symptoms of this error code are pretty much the same on all vehicles, their severity may differ from one make to another. Of course, it triggers the Check Engine light. Some of the other common symptoms are:

  • Reach-running or lean-running condition
  • Loss of power
  • Higher fuel consumption
  • Rough idling
  • Hard starting
  • Emission of black smoke on the tail pipe

Possible Causes

Common causes of this error code are:

  • Burnt wires (wires that runs too close to the hot components of the exhaust)
  • Short circuit caused by burnt wires
  • Bad ground connection
  • Bad connection due to impact damage from road debris or corrosion
  • Blown fuses on heater element circuit
  • Faulty or physical damage to HO2S
  • Heater control circuit open (for 12V PCM controlled systems)
  • Short in battery voltage (B+) in heater element circuit (for 12V PCM controlled systems)
  • Open ground circuit (for 12V PCM controlled systems)
  • Short to ground heater control circuit (for PCM ground control systems)

How to Check

As with error codes, troubleshooting for P0038 starts with a thorough visual check of all connectors and wirings associated with the troubled components. Check for any signs of damage, burnt, shorted or broken connectors and wirings. Fix and replace everything that is damaged.

Note that on some applications, fused circuit B requires input voltage. Make sure to check associated fuses in your initial inspection of the wiring.

If the error code is still there, perform the reference, continuity and resistance tests for all associated wiring.

Check the oxygen sensor for signs of discoloration or deposits. Aftermarket fuel and oil additives may contain compounds that are silicone-based, which can accumulate into the spark plugs and oxygen sensors. Note that, you can’t clean the oxygen sensor of any deposits. Your only viable remedy is to replace the sensor and use premium oil and fuel that guarantee no additives.

After replacing the sensor, retest and see if the code comes back again.

How to Fix

Aside from fixing damaged wiring and connectors, make sure you also check for bare wires, especially where wiring enters sensor. This usually causes shorts and fatigue. Wiring must be routed away from the exhaust. If necessary, repair or replace the sensor.

If wiring and connectors seem to be in good working condition, unplug the Bank 1, Sensor 2 HO2S and check whether it there is 12V B+ while the key is on and engine is off (or ground present, depending on the system). Check whether the heater control circuit is intact. If it is still intact, then remove the oxygen sensor and check it for any signs of damage. If you have access to the specs of the resistance, use the Ohmmeter and perform a resistance test to the heater element. Should you notice infinite resistance, open the heater. Replace the oxygen sensor if needed.

Note that, the overall condition and performance of the engine, has direct influence on the performance of the oxygen sensor. Thus, should there be any issues regarding poor combustion, exhaust leaks, vacuum leaks, excessive oil burning, etc., that affects the engine and exhaust system, there is little point in trying to diagnose and repair sensor-related problems. Thus, repair should be complete.