Chevrolet Equinox · Diagnostic Trouble Code
P0155 — O2 Sensor Heater Circuit Malfunction (Bank 2, Sensor 1)
What it means, how urgent it is, the most likely causes, and the exact order to diagnose it — with the repair guides that fix it.
What P0155 means
The internal heater brings the sensor to operating temperature within seconds of startup so fuel control goes closed-loop quickly. The PCM monitors the heater's current draw and sets P0155 when the circuit is open, shorted, or drawing abnormal current.
On V6 and V8 engines, Bank 2 is the side opposite cylinder 1. When P0155 appears together with P0135 (Bank 1's heater code), look at what the two banks share — usually a fuse, relay, or power feed — before buying two sensors.
⚠️ How urgent is it?
Repair before your emissions test. If P0135 is present too, check the shared heater fuse and relay first — one blown fuse explains both codes.
Most likely causes
- A burned-out heater element in the Bank 2 upstream oxygen sensor — the most common cause.
- Heater circuit wiring faults: blown fuse, damaged wires, corroded connector.
- Heat-related wiring degradation near the Bank 2 exhaust manifold.
- Rarely, a PCM heater-driver issue.
How to diagnose it — in order
-
1
Check the heater fuse — shared fuses can take out both banks' heaters at once.
-
2
Measure heater resistance at the Bank 2 Sensor 1 connector with the sensor unplugged; open circuit condemns the sensor.
-
3
Confirm battery voltage at the heater feed wire, key on.
-
4
Trace the Bank 2 harness for melted or chafed sections near the manifold.
-
5
If both P0135 and P0155 set together, suspect the shared fuse, relay, or power feed before replacing two sensors.
Reading the code is step zero
A basic OBD2 scanner plugs into the port under your dash and tells you exactly which codes are stored — plus freeze-frame data showing what the engine was doing when the code set.
View OBD2 scanners on AmazonAs an Amazon Associate we earn from qualifying purchases.
Repair guides that fix P0155
General diagnostic information, not a factory service procedure. If you're unsure, have a qualified technician confirm the diagnosis before buying parts.