What Does P0155 Mean?
The O2 sensor heater circuit for Bank 2, Sensor 1 (upstream, pre-catalytic converter) has been detected as malfunctioning. The heater is critical for bringing the sensor to its operating temperature (600-650°F) quickly after a cold start, enabling closed-loop fuel control. Without a functioning heater, the sensor takes several minutes to warm up from exhaust heat alone, during which the engine runs in open loop with richer fuel mixture. The driver may notice increased fuel consumption during warm-up.
Common Causes
40%
Burned-out or open O2 sensor heater element
20%
Blown heater circuit fuse or failed relay supplying power to the heater
20%
Wiring harness damage or open circuit in the heater power or ground wires
10%
Corroded or water-damaged connector at the O2 sensor causing high resistance
10%
PCM heater ground driver circuit failure
Diagnostic Steps
1
Measure the O2 sensor heater resistance at the sensor connector (disconnect sensor first) — typical range is 2-25 ohms; an open reading (OL) confirms the heater element has failed.
2
Verify 12V battery voltage is present at the heater power wire with key on, engine running — no voltage points to a blown fuse, bad relay, or wiring open.
3
Check the heater fuse in the underhood fuse box — if blown, inspect the heater circuit for shorts before replacing the fuse.
4
Verify the PCM provides a ground to the heater control wire by back-probing the connector and checking for ground with the engine running — no ground indicates a PCM driver issue.
5
Use an amp clamp on the heater wire to verify current draw (typically 0.5-2.0A) — zero current with voltage present and good ground confirms the heater element is open internally.
Estimated Repair Cost
$80 - $300
Parts + labor, varies by vehicle and location
The O2 sensor heater circuit for Bank 2, Sensor 1 (upstream, pre-catalytic converter) has been detected as malfunctioning. The heater is critical for bringing the sensor to its operating temperature (600-650°F) quickly after a cold start, enabling closed-loop fuel control. Without a functioning heat...
The most common cause of P0155 (O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 1)) is: Burned-out or open O2 sensor heater element
Typical repair costs for P0155 range from $80 to $300, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving. The sensor will eventually warm up from exhaust heat and function normally. The main impact is extended open-loop operation during warm-up (richer mixture, higher emissions, worse fuel economy). The vehicle will fail emissions testing.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0155 to identify the root cause.
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Quick Info
Category
Powertrain
System
Emissions / Exhaust System
Difficulty
Type
Generic (SAE)
Recommended Tools
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