If your OBD-II scanner displays P0055, your vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected that the heater resistance of the Heated Oxygen Sensor (HO2S) on Bank 2 Sensor 2 is outside the manufacturer’s expected operating range.
The generic SAE definition for P0055 is:
HO2S Heater Resistance Bank 2 Sensor 2
Unlike heater control circuit codes that monitor voltage or current, P0055 specifically indicates the ECM has determined the internal heater element resistance is either too high, too low, or completely outside specification.
Bank 2 Sensor 2 is the downstream oxygen sensor located after the catalytic converter on the side of the engine opposite cylinder number one.
Depending on the manufacturer, this sensor may also be called:
- Heated Oxygen Sensor (HO2S)
- Rear Oxygen Sensor
- Downstream Oxygen Sensor
- Post-Catalytic Converter Oxygen Sensor
- Lambda Sensor
- Catalyst Monitoring Sensor
- Rear Air/Fuel Ratio Sensor (some manufacturers)
Common causes of P0055 include:
- Failed oxygen sensor heater
- Aging heater element
- Open heater circuit
- High heater resistance
- Corroded connector
- Damaged wiring
- Incorrect replacement oxygen sensor
- Poor ground
- Weak charging system
- Failed ECM (rare)
Although P0055 rarely causes drivability issues, it can prevent catalyst monitoring, increase emissions, and cause your vehicle to fail an emissions inspection.
For additional diagnostic information, visit:
- Complete OBD-II Code Library: https://my.prostreetonline.com/dtc-obdii/
- Body B-Code Library: https://my.prostreetonline.com/dtc-doctor/b-code-obd-ii-codes/
- Chassis C-Code Library: https://my.prostreetonline.com/dtc-doctor/c-code-obd-ii-codes/
P0055 Quick Facts
| Item | Information |
|---|---|
| OBD-II Code | P0055 |
| Description | HO2S Heater Resistance Bank 2 Sensor 2 |
| Category | Powertrain |
| System | Emissions |
| Sensor | Bank 2 Sensor 2 |
| Sensor Location | Downstream (After Catalytic Converter) |
| Severity | Low |
| Safe to Drive? | Yes |
| Typical Repair Cost | $100–600 |
What Does P0055 Mean?
P0055 means the ECM has detected that the electrical resistance of the heater inside the downstream oxygen sensor on Bank 2 is outside the calibrated operating range.
Every heated oxygen sensor contains an internal electric heating element.
The heater allows the sensor to:
- Reach operating temperature rapidly
- Begin catalyst monitoring sooner
- Reduce emissions after startup
- Complete OBD-II readiness monitors
- Improve emissions testing accuracy
If the heater resistance changes beyond acceptable limits, the ECM stores P0055.
Unlike P0039 or P0056, P0055 does not necessarily indicate a wiring failure—it specifically points toward the heater element or excessive circuit resistance.
What Is Bank 2 Sensor 2?
Bank 2 refers to the side of the engine that does not contain cylinder number one.
Sensor 2 is the oxygen sensor positioned after the catalytic converter.
Its primary responsibilities include:
- Monitoring catalytic converter efficiency
- Verifying oxygen storage capacity
- Confirming emissions system performance
- Assisting OBD-II readiness monitors
- Detecting catalyst deterioration
Unlike upstream oxygen sensors, the downstream sensor generally does not directly control fuel trims.
Why Does the Downstream Oxygen Sensor Have a Heater?
Modern emissions regulations require catalytic converter monitoring shortly after startup.
Without an electric heater, the downstream oxygen sensor would require significantly more time before producing reliable readings.
The heater allows the ECM to:
- Complete catalyst monitoring sooner
- Reduce cold-start emissions
- Shorten emissions readiness time
- Improve diagnostic accuracy
- Detect catalyst problems earlier
How the Heater Resistance Is Monitored
The ECM continuously evaluates:
- Heater resistance
- Heater current
- Supply voltage
- Warm-up rate
- Sensor response
The ECM knows approximately what resistance the heater should have.
If resistance becomes:
- Too high
- Too low
- Open
- Intermittent
P0055 is stored.
This diagnostic is different from heater circuit codes because the circuit itself may still function electrically while the heater element has degraded internally.
P0055 vs Related Codes
| Code | Description |
| P0036 | Heater Control Circuit Bank 1 Sensor 2 |
| P0037 | Heater Circuit Low Bank 1 Sensor 2 |
| P0038 | Heater Circuit High Bank 1 Sensor 2 |
| P0054 | Heater Resistance Bank 1 Sensor 2 |
| P0055 | Heater Resistance Bank 2 Sensor 2 |
| P0056 | Heater Control Circuit Bank 2 Sensor 2 |
Generally:
- Circuit codes monitor electrical operation.
- Resistance codes evaluate heater health.
Symptoms of P0055
Common symptoms include:
- Check Engine Light
- Failed emissions inspection
- Catalyst monitor incomplete
- Increased cold-start emissions
- Readiness monitors not completing
Most drivers notice no change in performance.
Common Causes of P0055
1. Aging Heater Element
The internal heater gradually changes resistance after years of repeated heating and cooling cycles.
This is the most common cause.
2. Failed Oxygen Sensor
Internal heater damage eventually moves resistance outside specification.
Replacement is usually required.
3. Open Heater Element
The heater may fail completely, resulting in infinite resistance.
4. Corroded Connector
Connector corrosion increases circuit resistance.
Inspect for:
- Green corrosion
- Loose terminals
- Moisture
- Bent pins
- Broken connector locks
5. Damaged Wiring
Inspect the harness for:
- Heat damage
- Broken conductors
- Chafed insulation
- Previous poor repairs
- Road debris damage
6. Poor Ground
High resistance in the ground circuit can affect heater performance.
Verify ground integrity before replacing the sensor.
7. Incorrect Replacement Sensor
Universal oxygen sensors often use heater elements that differ from OEM specifications.
Direct-fit sensors are strongly recommended.
8. Weak Charging System
Low charging voltage may interfere with heater diagnostics.
Inspect:
- Battery
- Alternator
- Battery terminals
- Engine grounds
9. Failed Heater Relay
Some vehicles power several heater circuits through one relay.
A weak relay may reduce heater performance.
10. ECM Driver Failure
Extremely uncommon.
Only suspect the ECM after verifying:
- Heater resistance
- Wiring
- Connectors
- Voltage
- Ground
Is P0055 Serious?
P0055 is considered a low-severity diagnostic trouble code.
The vehicle generally remains safe to drive.
However, ignoring the code can result in:
- Increased emissions
- Failed emissions testing
- Catalyst monitor failure
- Additional oxygen sensor codes
- Reduced diagnostic capability
Can You Drive With P0055?
Yes.
Because Bank 2 Sensor 2 primarily monitors catalyst performance rather than fuel delivery, most vehicles continue driving normally.
The only thing likely to suffer immediately is your emissions readiness monitor—and perhaps your patience when inspection time arrives.
How to Diagnose P0055
Step 1: Scan for Additional Codes
Look for:
- P0054
- P0056
- P0057
- P0058
- Catalyst efficiency codes
- Battery voltage codes
Record freeze-frame data before clearing anything.
Step 2: Locate Bank 2 Sensor 2
Confirm:
- Cylinder number one
- Bank 2
- Downstream sensor
Replacing the wrong sensor remains surprisingly common.
Step 3: Inspect Wiring
Look for:
- Burned wiring
- Heat damage
- Chafing
- Broken insulation
- Previous repairs
Pay close attention to wiring near the catalytic converter.
Step 4: Inspect Connector
Inspect for:
- Moisture
- Corrosion
- Bent terminals
- Loose pins
- Broken locking tabs
Step 5: Measure Heater Resistance
Disconnect the sensor.
Measure resistance across the heater terminals.
Possible results include:
- Infinite resistance
- Excessively high resistance
- Very low resistance
- Within specification
Compare measurements with manufacturer specifications.
Step 6: Verify Power Supply
Check:
- Battery voltage
- Heater fuse
- Relay operation
- Ground integrity
Step 7: Perform Voltage Drop Testing
Voltage-drop testing helps identify:
- High-resistance connectors
- Corroded terminals
- Weak grounds
- Damaged wiring
Step 8: Compare With Bank 1 Sensor 2
If both downstream sensors are identical, compare:
- Heater resistance
- Warm-up rate
- Current draw
Differences often identify the faulty sensor.
Step 9: Replace the Sensor if Necessary
If heater resistance is outside specification, replace Bank 2 Sensor 2 with a quality OEM-equivalent direct-fit sensor.
Step 10: Verify Repair
After repairs:
- Clear all DTCs.
- Perform a cold start.
- Monitor heater operation.
- Complete a drive cycle.
- Confirm readiness monitors complete.
- Verify P0055 does not return.
Common Repairs and Costs
| Repair | Estimated Cost |
| Oxygen sensor replacement | $150–500 |
| Wiring repair | $100–400 |
| Connector replacement | $75–250 |
| Heater relay replacement | $50–200 |
| Fuse replacement | $10–50 |
| Battery or charging repair | $150–400 |
| ECM replacement | $1,000–2,500+ |
Common Diagnostic Mistakes
Avoid these common mistakes:
- Replacing Bank 1 instead of Bank 2
- Replacing Sensor 1 instead of Sensor 2
- Installing universal oxygen sensors
- Ignoring connector corrosion
- Skipping voltage-drop testing
- Assuming resistance automatically confirms heater performance
- Replacing the ECM before testing the circuit
Vehicles Commonly Affected
P0055 commonly appears on:
- Chevrolet
- GMC
- Ford
- Dodge
- Chrysler
- Jeep
- Toyota
- Lexus
- Honda
- Acura
- Nissan
- Infiniti
- Hyundai
- Kia
- Subaru
- Volkswagen
- Audi
- BMW
- Mercedes-Benz
- Volvo
Exact heater specifications vary by manufacturer.
How to Prevent P0055
Reduce the likelihood of P0055 by:
- Installing OEM-quality oxygen sensors
- Keeping heat shields intact
- Repairing oil and coolant leaks
- Protecting wiring from exhaust heat
- Cleaning electrical connectors
- Maintaining battery and charging system health
- Avoiding universal splice-in sensors
Frequently Asked Questions
What does P0055 mean?
P0055 indicates the heater resistance of the Bank 2 Sensor 2 oxygen sensor is outside the manufacturer’s specification.
Is P0055 serious?
Usually not.
Most vehicles continue operating normally.
Can I drive with P0055?
Yes.
The downstream oxygen sensor primarily monitors catalytic converter performance rather than fuel delivery.
What causes P0055?
The most common causes include:
- Aging heater element
- Failed oxygen sensor
- Damaged wiring
- Corroded connector
- Incorrect replacement sensor
Will replacing the oxygen sensor fix P0055?
In most cases, yes.
However, wiring and connectors should always be inspected before replacing components.
Is P0055 the same as P0056?
No.
P0055 monitors heater resistance.
P0056 monitors the heater control circuit.
Does P0055 affect fuel economy?
Usually very little.
The downstream sensor has minimal influence on fuel control.
Can P0055 cause a failed emissions inspection?
Yes.
If readiness monitors cannot complete or catalyst monitoring is affected, the vehicle may fail inspection.
Final Thoughts
The P0055 code indicates the ECM has detected abnormal heater resistance in the Bank 2 Sensor 2 heated oxygen sensor. In most cases, this points to an aging heater element inside the downstream oxygen sensor, although damaged wiring, corroded connectors, poor electrical connections, and incorrect replacement sensors can produce the same fault.
Because the downstream sensor primarily monitors catalytic converter performance, most drivers won’t notice any changes in engine performance. However, ignoring P0055 can delay readiness monitors, increase emissions, and prevent the vehicle from passing an emissions inspection. A careful inspection of the wiring, connector, and heater resistance before replacing the sensor will help ensure an accurate repair.
Related Articles
Bank 2 Sensor 2 Heater Codes
- P0056 Code Explained: HO2S Heater Control Circuit Bank 2 Sensor 2
- P0057 Code Explained: HO2S Heater Control Circuit Low Bank 2 Sensor 2
- P0058 Code Explained: HO2S Heater Control Circuit High Bank 2 Sensor 2
Heater Resistance Codes
- P0053 Code Explained: HO2S Heater Resistance Bank 1 Sensor 1
- P0054 Code Explained: HO2S Heater Resistance Bank 1 Sensor 2
- P0059 Code Explained: HO2S Heater Resistance Bank 2 Sensor 1
Browse the complete Pro Street diagnostic libraries:
- Complete OBD-II Guide: https://my.prostreetonline.com/dtc-obdii/
- B-Code Guide: https://my.prostreetonline.com/dtc-doctor/b-code-obd-ii-codes/
- C-Code Guide: https://my.prostreetonline.com/dtc-doctor/c-code-obd-ii-codes/
