OBD-II trouble code
P0042: HO2S Heater Control Circuit (Bank 1, Sensor 3)
SAE J2012: heater control circuit, bank 1 sensor 3. Sensor 3 is the third sensor in airflow order. The 2014 Golf specification book carries this code in the CBUA section and marks the low and high companions CBUA only. Many engines have no sensor 3.
Quick facts
- System
- Powertrain
- Category
- Oxygen Sensor
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $300 – $580 (oxygen sensor replacement, parts and labor)
- DIY difficulty
- Intermediate DIY
Browse every code in P0001–P0099, or start from the full code library.
What does P0042 mean?
SAE J2012 APR2002 names P0042 HO2S Heater Control Circuit, Bank 1 Sensor 3. Section 3.1 is the circuit/open description: a fixed value or no response. Section 3.6 numbers sensors in airflow order. Sensor 3 is the third. Figures 1 through 3 draw a third heated sensor farther down the pipe on those example engines. If the diagram shows only two oxygen sensors, this code is not the one that pipe uses.
The 2014 Volkswagen Golf, GTI, and Golf R Quick Reference Specification Book (NHTSA MC-10122269), engine codes CBTA and CBUA, has a row labeled P0042 O2 Sensor Heater Control Circuit Bank 1 Sensor 3, and the extract marks it CBUA only. The low and high rows under it, P0043 and P0044, are also marked CBUA only. The voltage cells in that extract do not stay tied to the code names, so no volt threshold is repeated. CBUA is the engine code that book is using for those rows. It is not a repair for every Golf.
The 2005 GM 3.8L L26 mode-6 file that defines P0030, P0036, P0053, and P0054 does not, in the pages read, define P0042. Do not move the 3.8L driver test onto sensor 3.
Bank 1 still means the bank with cylinder 1. On a single-bank engine, sensor 3 is the third sensor on that one pipe, not a second bank.
Common causes
- An open or a fixed heater-driver state on bank 1 sensor 3, which is the circuit/open definition
- A vehicle with two oxygen sensors being tested for a third sensor it does not have
- The CBUA-only rows in the 2014 Golf book used on a different engine code
- Connector or harness damage at the rearmost sensor, confirmed on this pipe
- Sensor 2 replaced because the count started at the wrong end of the exhaust
- A resistance code, P0055, diagnosed with this circuit code's steps
Symptoms
- Check engine light with P0042
- On a 2014 Golf with engine code CBUA, the heater-circuit row that book prints for sensor 3
- No sensor 3 on the diagram, which means the stored code needs the calibration checked before a part is ordered
- The rear sensor slow to heat after a cold start, if this monitor is the heater driver
- P0043 or P0044 stored beside it only on a calibration that separates low and high
- The underbody connector for the third sensor, when the diagram shows one
Diagnostic steps
- 1.Count the oxygen sensors on the diagram from the engine toward the tailpipe. Sensor 3 is the third. If the diagram stops at sensor 2, stop and confirm the code and the calibration before you order a part.
- 2.On a 2014 Golf, use the CBUA section of the January 2014 specification book only when the engine code is CBUA. That section is marked CBUA only for the sensor 3 heater rows. Other engine codes in the same book use other rows.
- 3.Ignition off. Unplug the sensor 3 connector. If it is under the vehicle, the vehicle is on a lift or stands and the exhaust is cool. Inspect the terminals.
- 4.Check supply, open, short to ground, and short to power on the heater control, module disconnected for the resistance checks. Circuit/open does not mean you skip the short-to-ground check.
- 5.Measure the heater only to a spec this procedure prints. No universal ohm band was found for P0042. The 2005 3.8L windows are for P0053 and P0054 on sensors 1 and 2 of that engine.
- 6.Replace sensor 3 only when the sensor side fails and the wiring passes. Clear the code and run the monitor. Do not replace a catalytic converter from a heater-circuit code.
Repair cost
$300 – $580 (oxygen sensor replacement, parts and labor)
RepairPal does not publish a separate price for sensor 3. The pair is the oxygen-sensor job: national average $440–$523, labor $93–$136, parts $347–$387, updated 3 September 2026. The low named example on the near-me page is a Chevrolet Silverado 1500 at $306–$407. The high named example is a Honda CR-V at $501–$578. Access for a third sensor changes the labor time in the service information. It does not have its own RepairPal line. A connector repair is outside the pair.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with oxygen sensor replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.