HO2S Heater Resistance Bank 1 Sensor 3 (PCM)
The oxygen sensor heater for Bank 1, Sensor 3 (located after the catalytic converter) isn't working properly, like a faulty heating element in a toaster that won't warm up. The PCM detected the heater circuit is drawing too much current or has excessive resistance, preventing the sensor from reaching operating temperature quickly.
The PCM monitors the heater circuit's resistance and current draw during sensor warm-up. It expects the heater to pull a specific current range and reach operational temperature within a set time window. If resistance is too high or current draw is abnormal, the fault code sets.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Heater Circuit Current | 0.5–2.0 amperes | >2.0 A or <0.1 A (open circuit) |
| Warm-Up Time | <10 seconds to 0.6V output | >15 seconds or no voltage rise |
Code P0055 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0055 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.