Skip the auto shop - Our mechanics make house calls

P0030 OBD-II Trouble Code: HO2S Heater Control Circuit (Bank 1 Sensor 1)

check engine light logo

P0030 Trouble code definition

P0030 is the code for HO2S Heater Control Circuit (Bank 1 Sensor 1)

What the P0030 code means

P0030 indicates for the engine to operate properly, the engine exhaust should have a specific air-fuel ratio of 14.7 to 1 as determined by the heated oxygen sensors (HO2S) which detect the oxygen content of the exhaust. This information is then sent to the engine control module (ECM) to adjust the fuel delivered to the engine.

An HO2S is heated to ensure very rapid response of data to the ECM’s closed loop system which helps decrease emissions during start-up and when the engine is cold.

What causes the P0030 code?

Generally, if the code is cleared and reset, and the engine warning light comes back on along with the OBD-II code, this means that the HO2S sensor for the engine bank 1 and sensor 1 is not sending the proper signals to the ECM.

The ECM may be defective or has defective wiring. However, it is quite rare that the ECM is bad.

What are the symptoms of the P0030 code?

  • The Check Engine Light will come on.

  • With the O2 heater circuit not working the O2 sensor response time will be affected and the sensor will not respond to fuel and oxygen in the exhaust for the first 3 to 5 minutes of running or more.

  • The lack of response will affect the ECM ability to control the fuel mixture and it will go into a fixed fuel mix until the problem is fixed.

How does a mechanic diagnose the P0030 code?

P0030 is diagnosed with an OBD-II scanner. The mechanic can reset the OBD-II code and then test drive the vehicle to see if the engine warning light and code returns. If it comes back on, the mechanic should check both power and ground to the sensor, including inspecting the wiring and sensor.

Many of the problems for this code are wiring related, due to the heat of the exhaust.

Common mistakes when diagnosing the P0030 code

  • Do not assume that the HO2S is bad and replace the HO2S before checking that all of the related wiring and the connector closely.

  • The mechanic should ensure there are 12 volts to the sensor and the ground is good.

  • Both sides of the connector wiring need to be check to ensure that the connector is good and not damaged.

How serious is the P0030 code?

The P0030 code will usually be preceded by the engine warning light coming on the vehicle’s dash while it is in operation. The vehicle can still be driven but it should be properly diagnosed as soon as possible to prevent problems like the sensor loop failing, excessive fuel consumption, poor operation, or damage to other components.

Often times, if the engine warning light came on immediately at start up, the OBD-II system can be reset and the vehicle will operate normally.

What repairs can fix the P0030 code?

The most common repairs to address the P0030 code are as follows:

  • Have a certified technician from verify the code with a scanner. Reset the fault codes and perform a road test.

  • If the P0030 code returns, then follow the test procedure. It can have several problems, but wiring being damaged by excessive heat from the exhaust is most common. Make certain the wiring is in good condition and has proper voltage and ground to the sensor before replacing the sensor.

  • With key on and the engine off use a voltmeter to check for 12+ volts fused battery feed to the heater element. If there is no voltage present, repair open or short in the 12 volt feed circuit but first determine if it is necessary to replace any fuse blown from the short.

  • If the battery feed is correct, remove the ground (control) circuit from the ECM wiring connector and check for resistance on the circuit. If there is infinite resistance, repair the open in the circuit.

  • If the control circuit is good, suspect a bad O2 sensor. Replace and re-check.

The P0030 code is a relatively common situation as it is located in front of the catalytic converter and gets considerable heat generated from the converter.

In one instance, I found that after a visual and electrical test of the system that wires coming from the #1 HO2S were run above the exhaust pipe in a way that had no slack to put them on the wiring hanger. This caused all of the wires on the sensor to melt to the exhaust pipe and ground out the power and sensor wires causing the warning light to come on immediately.

During some maintenance service at another shop or dealer, someone had disconnected the sensor wires and apparently did not like the way the wires were routed, so they thought it would be better to run them above the pipe. The wires from the sensor were designed to go straight up and be held in place with a special bracket that supported the connector away from the pipe. I had to replace the sensor, reattach the wires correctly, reset code, then road test it with no issues noted. Many problems are created by the people who work on the vehicles.

Additional comments for consideration regarding the P0030 code

Many vehicles with mileage over 100,000 have momentary sensor problems that usually occur during start up or prolonged stress situations on the drive train. If the engine warning light comes on and the vehicle seems to be operating normally, the OBD-II system can be reset using the scanner and the problem may not reoccur. This is why it is important to verify the fault and reset it before doing any repairs.

Need help with a P0030 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.


Post a question and get free advice from our certified mechanics.


More related articles

Symptoms of a Bad or Failing Flexible Clutch Hose
Common signs include difficulty shifting, low clutch fluid, and feeling no resistance at the clutch pedal.
P0222 OBD-II Trouble Code: Throttle/Pedal Position Switch/Sensor B Circuit Low Input
P0222 code definition Throttle/Pedal Position Switch/Sensor B Circuit Low Input What the P0222 code means The manufacturer specifies a range of acceptable voltage to be produced from the throttle position...
Insurance Requirements for Car Registration in Kentucky
The Kentucky Transportation Cabinet requires that all drivers in Kentucky carry liability automotive insurance, or “financial responsibility” in order to operate a vehicle legally and maintain vehicle...

Related questions

Q: Getting a check Engine light and codes

Both of those codes are for oxygen sensor issues. Oxygen sensors needs to heat up before it gives good readings. In pre 1996 cars, the sensor would get heated up by the cars exhaust. This took about 2 minutes. Oxygen...

Q: Can I Look Up What Trouble Codes Mean?

When your Check Engine Light comes on or flashes on the dash for you it is indicating there is a problem in one of the vehicle systems and has set a trouble code stored in one of the modules’ memory....

Q: I recently had a new stereo installed in my mirage, and now the airbag light is on. How do i reset it or get it to go out.

The Air Bag Light would set a code in the computer and should be checked by the dealer since you are still under factory warranty unless the stereo installer damaged the wiring or something to do with the airbag. I...