P0155
O2 Sensor Heater Circuit Malfunction Bank 2 Sensor 1
The engine computer found a problem in the heater circuit for the front oxygen sensor on bank 2. That heater helps the sensor warm up quickly so the engine can control fuel mixture properly. When it fails, the engine may run richer, use more fuel, and set a check engine light.
- SEV
- 3/5
- DRIVE
- CAUTION
- DIY
- $20–$150
- SHOP
- $120–$450
Quick answer
AI-CITATION READYWhat it means
Can you drive with it?
Most common causes
- Failed bank 2 sensor 1 oxygen sensor heater element
- Damaged, corroded, or melted wiring near the sensor or exhaust
- Blown heater circuit fuse or shared power supply issue
Typical repair cost
DIY usually runs $20–$150. Typical shop repair lands around $120–$450, depending on the root cause.
01 / Definition
P0155 indicates the powertrain control module detected a malfunction in the heater circuit of the upstream oxygen sensor on bank 2, sensor 1. The fault may be an open circuit, short, blown fuse, failed heater element, damaged wiring, or poor electrical connection. Because the heater is needed for fast sensor warm-up, the code can affect closed-loop fuel control and emissions.
02 / Drive status
With caution. You can usually drive short distances, but the engine may use more fuel and run less cleanly. Have it checked soon, especially if the engine runs rough or the check engine light is flashing.
03 / Symptoms
- Check engine light on
- Reduced fuel economy
- Rough running during cold start
- Delayed closed-loop operation
- Failed emissions test
- Possible rich or lean fuel trim symptoms
04 / Causes
| 1 | Failed bank 2 sensor 1 oxygen sensor heater element | high |
|---|---|---|
| 2 | Damaged, corroded, or melted wiring near the sensor or exhaust | high |
| 3 | Blown heater circuit fuse or shared power supply issue | medium |
| 4 | Poor connector contact, loose plug, or water intrusion at the sensor connector | medium |
| 5 | Faulty relay, PCM driver problem, or related circuit control issue | low |
| 6 | Incorrect aftermarket sensor or installation problem | low |
05 / Diagnostic sequence
- 01Verify the code and check for related oxygen sensor or heater circuit codes.
- 02Inspect the bank 2 sensor 1 wiring harness and connector for heat damage, corrosion, looseness, or broken wires.
- 03Check the oxygen sensor heater fuse and any related relay or power feed.
- 04Measure heater circuit resistance at the sensor and compare it to manufacturer specifications.
- 05Check for battery voltage and ground at the heater circuit with the key on, if applicable.
- 06Inspect the harness routing near the exhaust for melted insulation or intermittent contact.
- 07If wiring and power are correct, test or replace the sensor and verify the code does not return.
06 / Repairs
| 1 | Repair damaged wiring, terminals, or connector at bank 2 sensor 1 | $20–$150 |
|---|---|---|
| 2 | Replace blown fuse or faulty relay if the heater circuit lost power | $10–$80 |
| 3 | Replace the bank 2 sensor 1 oxygen sensor if its heater has failed | $50–$250 |
| 4 | Diagnose and repair PCM control circuit issues if wiring and sensor test good | $150–$600 |
07 / Related codes
08 / FAQ
What is bank 2 sensor 1?
It is the upstream oxygen sensor on the side of the engine that does not contain cylinder 1.
Can a bad oxygen sensor heater cause poor gas mileage?
Yes. If the heater does not work, the engine may stay in warm-up fuel settings longer and use more fuel.
Is P0155 usually the sensor itself?
Often yes, but wiring, connectors, and fuse problems are also common and should be checked first.
Will clearing the code fix it?
No. The code will usually return until the heater circuit problem is repaired.
09 / Source and method
- DATA BASIS
- OBD-II REFERENCE + OBD2.HELP
- METHOD
- STATIC VALIDATION
- SAFETY
- INFORMATIONAL
This page combines OBD-II diagnostic reference data with OBD2.help generated diagnostic guidance for code meaning, likely causes, and repair direction.
Publishing uses deterministic schema and build validation, plus manual spot checks on representative pages before release.
Safety-critical diagnosis and repairs should be confirmed with a qualified mechanic, especially when the vehicle is misfiring, overheating, or losing power.