P0036: Heater Oxygen Sensor Control (HO2S) Circuit (Bank 1, Sensor 2)

What is P0036?

Code P0036 is one of the diagnostic trouble codes (DTC), defined as “Heater Oxygen Sensor Control Circuit (Bank 1, Sensor 2).” It’s a generic powertrain code that applies to OBD-II equipped vehicles.

Fault code P0036 is triggered when the Engine Control Module (ECM) detects a potential problem with the heater circuit (heater element) in the downstream oxygen sensor located near Bank 1 (the engine side with cylinder #1.) This sensor is placed past the exhaust manifold, behind the catalytic converter, which is why it’s also called a rear O2 sensor.

The downstream oxygen sensor is primarily used for post catalyst monitoring of the oxygen content in the exhaust gas. 

Most modern vehicles use a heated oxygen sensor (HO2S) with a heater element circuit that quickly brings the sensor to operating temperature. The PCM controls the HO2S heater circuit based on the signals from the engine coolant temperature and engine load. 

The heated downstream sensor has to reach the optimal operating temperature (typically 570°F) to ensure that it sends an accurate voltage signal to the PCM. 

The faster the heated oxygen sensor reaches the operating temperature, the faster the sensor will start sending an accurate signal. The heater circuit minimizes the time needed for this to happen.

So if the PCM detects a fault within the Bank 1 Sensor 2 heating element circuit, it will trigger code P0036 and illuminate the Check Engine Light.

Common symptoms

In most cases, the P0036 fault code will not display any physical symptoms apart from the Check Engine Light. 

However, you can still keep an eye out for these potential signs in case they show up: 

• Decreased fuel performance
• Decrease in catalytic converter efficiency
• Driveability issues like rough idling or engine noise
• Failed emissions test or smoke test
• PCM turns the Engine Light on, etc.

Can I still drive?

Fault code P0036 is generally not considered to be serious. So it’s pretty safe to momentarily drive with the P0036 code, at least until you can find a mechanic. 

However, code P0036 may sometimes cause the PCM to turn on the vehicle’s failsafe mode. In that case, you may face driveability issues such as rough idling, poor fuel performance, engine noise, etc.

P0036 causes

Code P0036 can be caused by several reasons, including a bad O2 sensor or damaged wiring. 

Here’s a list of possible P0036 code triggers: 

• The oxygen sensor heater circuit is open, short, or draws too much current based on coolant temperature
• The wiring to the O2 sensor heater circuit is damaged, frayed, or the heated oxygen sensor connector is loose
• The heated oxygen sensor has high resistance
• The heated oxygen sensor at Bank 1 Sensor 2 is faulty or malfunctioning
• The exhaust system ground strap may be worn or corroded
• A faulty Engine Control Module (ECM) or a Powertrain Control Module (PCM)

Diagnosis

Here’s how a mechanic would diagnose fault code P0036:

1. Connect the car to an OBD-II scanner. Reset the Engine Light codes and perform a road test to see if the Check Engine Light turns on. 
2. Check the wiring system of the sensor. Test the O2 sensor heater circuit wiring using a digital multimeter or DVOM (digital Volt-Ohm meter). If the reading says OL (over limit), that means there’s an open circuit.
3. Check the battery voltage of the fused battery. If there is no voltage, there might be a short in the circuit. Check the sensor heating element to determine whether it’s an open circuit fault or high resistance. If the circuit is working, your car probably has a bad heated oxygen sensor (HO2S).
4. Back-probe the connector’s ground wire and inspect for resistance between the connector to the O2 sensor and the resistance of the good ground. 
5. If both power and ground are good, inspect the heated oxygen sensor fuse and check if that may need replacement. 

Note: A wiring diagram of the O2 sensor heater circuit can help identify where to test the resistance.

Possible repairs for P0036 & Costs

Code P0036 is generally triggered by a faulty or melted wire caused by an overheated O2 sensor heater circuit. However, it also has several other causes. 

Here are the repairs you may need to fix code P0036: 

• Replace any blown or damaged heated oxygen sensor fuse in the O2 sensor heater circuit
• Repair any damaged or frayed wire within the circuit
• Replace or repair the rear O2 sensor (rare)
• Replace or repair the wiring harness (rare)

Repair costs:

The P0036 code can be pretty inexpensive to repair. However, if you ignore it for too long, it may quickly escalate to more costly repairs. 

In general, you can expect to pay anywhere from $50 to $150 (including labor costs) to replace a blown fuse or damaged wiring. 

Other repair costs include: 

• Faulty O2 sensor replacement: $561 – $590
• Wiring harness replacement: $1,300 – $1,700