O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
What does P0155 mean?
The P0155 code means the vehicle's onboard diagnostic system has detected: O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1). This is a moderate severity code.
Common Symptoms
- Check Engine Light on
- Poor fuel economy during cold starts
- Engine runs rich during warm-up on bank 2
- Possible rough idle when cold
- Increased cold-start emissions
Probable Causes (Ranked by Likelihood)
- Failed O2 sensor heater element Very High
- Blown O2 sensor heater fuse High
- Open or shorted wiring in the heater circuit Moderate
- Corroded connector at the sensor Moderate
- PCM heater driver failure Low
Step-by-Step Diagnostic Procedure
-
Check the O2 sensor heater fuse and replace if blown.
-
Disconnect the bank 2 sensor 1 O2 sensor and measure heater resistance (2-15 ohms typical). Open or shorted readings indicate a failed heater.
-
Verify battery voltage at the heater power wire with the key on, engine off.
-
Check the ground circuit from the sensor connector to the PCM for continuity.
-
Inspect the wiring harness for heat damage, chafing, or breaks near the exhaust manifold.
Frequently Asked Questions
Can I drive with code P0155?
You can drive short distances. The O2 sensor on bank 2 will eventually warm up from exhaust heat alone, but this takes several minutes. During that time, the engine runs in open loop on bank 2, wasting fuel.
Is P0155 the bank 2 version of P0135?
Yes. P0135 is the heater circuit malfunction for bank 1 sensor 1, and P0155 is the same fault on bank 2 sensor 1. The diagnosis is identical.
Can a blown fuse cause P0155?
Yes. The heater fuse is one of the most common and easiest fixes. Check the underhood fuse box first. If the fuse is blown, replace it and check if it blows again, which would indicate a short in the circuit.