Failed oxygen sensor heater element (open circuit inside the sensor); Damaged or corroded wiring harness between the oxygen sensor and the engine control module; Blown fuse or faulty relay supplying power to the oxygen sensor heater circuit; Loose, corroded, or water-intruded connector at the oxygen sensor or at the engine control module; Open circuit in the heater ground path, including a poor chassis ground connection; Engine control module internal driver failure for the heater circuit (rare)

DTC codes / Volkswagen codes / P1120

P1120 · VolkswagenOxygen Sensor Heater Circuit Bank 2 Sensor 1 Open

Q: What does code P1120 mean?

Oxygen Sensor Heater Circuit Bank 2 Sensor 1 Open. P1120 on Volkswagen vehicles indicates that the engine control module has detected an open circuit in the heater element of the bank 2, sensor 1 oxygen sensor, which is the pre-catalyst sensor on the bank opposite cylinder one. The heater is responsible for bringing the sensor up to operating temperature quickly after a cold start, and an open circuit means the heater is not drawing current when commanded on.

P1120 on Volkswagen vehicles indicates that the engine control module has detected an open circuit in the heater element of the bank 2, sensor 1 oxygen sensor, which is the pre-catalyst sensor on the bank opposite cylinder one. The heater is responsible for bringing the sensor up to operating temperature quickly after a cold start, and an open circuit means the heater is not drawing current when commanded on.

SystemPowertrain

Code typeVolkswagen specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illuminated check engine light, often with no other noticeable symptoms
Slightly higher fuel consumption during the first few minutes after a cold start
A brief delay in entering closed-loop fuel control, which may cause a faint rich smell from the exhaust when cold
In rare cases, a rough idle or hesitation when the engine is cold
No drivability complaints once the engine is at operating temperature

Common causes, most likely first

Failed oxygen sensor heater element (open circuit inside the sensor)
Damaged or corroded wiring harness between the oxygen sensor and the engine control module
Blown fuse or faulty relay supplying power to the oxygen sensor heater circuit
Loose, corroded, or water-intruded connector at the oxygen sensor or at the engine control module
Open circuit in the heater ground path, including a poor chassis ground connection
Engine control module internal driver failure for the heater circuit (rare)

How to diagnose and fix it

Check the fuse and relay that supply power to the bank 2 sensor 1 oxygen sensor heater circuit and replace any failed component.
Inspect the oxygen sensor connector and the engine control module connector for corrosion, water intrusion, or loose pins, and clean or repair as needed.
Measure the resistance of the oxygen sensor heater element with a multimeter and compare it to the manufacturer's specification; an open circuit confirms a failed sensor.
Perform a voltage drop test on the heater power and ground circuits while the heater is commanded on to identify excessive resistance in the wiring.
Repair any damaged wiring or connectors in the heater circuit, then clear the fault memory and verify the code does not return.
If the wiring and connectors are good and the heater circuit tests correctly, replace the bank 2 sensor 1 oxygen sensor with a quality part.
After replacement, clear the fault memory, perform a road test with a cold start, and confirm the heater circuit monitor passes.

Why the heater circuit fails before the sensor does

The heater element inside the oxygen sensor is the most common failure point, but a corroded connector or chafed wire in the harness can mimic a failed sensor and lead to unnecessary replacement.
A blown fuse for the oxygen sensor heater circuit often indicates a shorted sensor heater or a wiring fault, so replacing the fuse without finding the root cause will usually result in the fuse blowing again.
On many Volkswagen models, the oxygen sensor heater circuit is powered through a relay that can fail intermittently, causing the code to set only under certain temperature or vibration conditions.
The engine control module may set P1120 even if the sensor heater still works intermittently, so a resistance check when the sensor is cold is more reliable than testing after the engine has warmed up.
This code does not always mean the sensor is completely dead; the sensor may still produce a signal, but the heater circuit open will prevent the system from entering closed-loop fuel control quickly, affecting emissions and fuel economy.

Can I keep driving with P1120?

You can usually continue driving with P1120, but the engine may run slightly richer during warm-up and fuel economy may suffer until the fault is repaired. Avoid extended idling from cold and have the circuit diagnosed soon to prevent increased emissions and potential catalytic converter damage over time.

Tools that help

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Guidance is general and written for Volkswagen vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.