Code
P0055
Generic
P — Powertrain
HO2S Heater Resistance Bank 1 Sensor 3
Views:
UK: 25
EN: 39
RU: 42
AI status
Completed
Completed
100%
Causes
- Open or high-resistance wiring in heater circuit
- Corroded, damaged, or disconnected oxygen sensor connector
- Failed heater element inside the oxygen sensor
- Blown fuse or failed relay supplying heater circuit
- Short to voltage or short to ground in heater wiring
- Poor ground or power distribution to the sensor heater
Symptoms
- Check Engine Light (MIL) illuminated
- Emissions test failure / readiness monitor not set
- Possible reduced fuel economy or rough idling (less common with downstream sensor faults)
- No obvious drivability symptoms in many cases
What to check
- Read and record freeze-frame and live data with a scan tool (heater status, oxygen sensor voltages, readiness monitors)
- Confirm code is current (not historic) and note drive cycle when set
- Visually inspect the sensor, wiring, and connector at Bank 1 Sensor 3 for damage, corrosion, heat damage, or contamination
- Check related fuses and relays for the oxygen sensor heater circuit
- Backprobe connector with connector disconnected to measure resistance of heater element
- Perform wiggle test on harness while monitoring for intermittent changes in the heater circuit status
Signal parameters
- Heater element resistance: typically low (single-digit to low tens of ohms) when good; open/infinite or high ohms indicates a problem (manufacturer spec varies)
- Supply voltage to heater circuit: battery voltage (~12 V) when power is present
- Control output: PCM may switch ground or apply a drive signal to energize heater — scan tool should show heater commanded on/off
- Current draw: when energized, heater draws noticeable current (hundreds of milliamps); abnormally low or zero current indicates open or high resistance
Diagnostic algorithm
- Verify DTC and note freeze-frame data with a scan tool. If multiple related heater codes exist, address the most likely common failure (fuses, relays, power/ground) first.
- Inspect sensor connector and harness for corrosion, heat damage, pin damage, or connector separation. Repair or clean as needed.
- Check relevant fuses/relays and verify power/ground at the sensor connector. Repair any blown fuses or corroded grounds.
- Unplug the sensor and measure heater resistance across the heater pins. Compare to manufacturer specification; infinite or very high resistance indicates failed heater element.
- If resistance is out of spec, check continuity from the sensor connector to the PCM for open circuit and for shorts to ground or battery. Repair wiring as required.
- With the connector back on, command the heater ON with a bi-directional scan tool and measure the voltage/current at the connector to confirm the PCM is commanding and the circuit is being supplied. If commanded but no supply, trace power feed. If supply present but no heater current, suspect sensor heater failure.
- If wiring and power/ground check good and heater element out of spec, replace the Bank 1 Sensor 3 oxygen sensor. After replacement, clear codes and perform a drive cycle to confirm the code does not return.
- If problems persist after sensor replacement, check PCM control output and re-evaluate wiring; consider PCM as last resort.
Likely causes
- Damaged connector or wiring harness to Bank 1 Sensor 3
- Internal heater failure of the downstream O2 sensor
- Corroded connector pins causing high resistance
- Blown fuse or damaged power/ground for heater circuit
Fault status
Status
Heater circuit for Bank 1 Sensor 3 has excessive resistance or open circuit. MIL may illuminate when the condition is confirmed by the engine control module.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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