P0135 means the PCM did not observe expected electrical behavior from the heater in Bank 1 Sensor 1, the upstream feedback sensor. Honda may name it a primary heated oxygen or air/fuel ratio sensor depending on year. Verify the exact connector and diagram, then test loaded battery feed, shared fuse/relay, terminal grip, heater resistance/current and PCM-controlled side. A resistance value or universal sensor copied from another CR-V generation can be wrong. Multiple heater codes strongly favor a shared feed or harness problem.
Match the symptom
Select the closest observation. The result changes the first test; it does not name a part to replace.
Capture heater command/current before exhaust heat changes resistance.
What can set P0135—and how to separate it
The order below is evidence-driven, not a universal probability ranking. Vehicle year, repair history, companion codes and the operating condition in freeze frame change where diagnosis should begin.
| Possible cause | Evidence that supports it | First useful test |
|---|---|---|
| Open upstream heater element | VIN-correct cold resistance/current test fails | Element resistance and current |
| Missing fused power | Voltage absent or collapses under load | Fuse/relay/feed voltage drop |
| PCM-control wire fault | Command exists but control path fails | Loaded control-circuit test |
| Heat/chafe/corrosion at harness | Visual or wiggle/temperature dropout | Connector/loom inspection |
| Incorrect replacement sensor | Fault began after repair; part/calibration mismatch | VIN part verification |
Honda sensor names evolved
Generic scanners may say oxygen sensor while Honda service information calls the upstream unit an A/F sensor.
Identify function and wiring, not only the generic label.
Loaded voltage exposes weak connections
A corroded terminal can show battery voltage with no current and fail when the heater turns on.
Voltage-drop and current tests reveal circuit capacity.
A blown fuse is a clue
Repeated opening points toward a shorted heater, chafed loom or another load on the branch.
A larger fuse can turn the fault into harness damage or fire.
Save these scan-data clues
Freeze frame is a snapshot of conditions when the PCM matured the fault. It can distinguish an idle-only problem from a load, cold-start or monitor-completion problem. Clearing first throws that context away.
- Battery voltage, ECT and time since start
- Heater command/current if supported
- All heater/voltage codes
- Fuse state
- Recent exhaust/engine work
- Engine, emissions label and sensor part
A practical diagnostic workflow
- 01Identify upstream sensor
Bank 1 Sensor 1 is before the monitored catalyst; connector route varies.
- 02Read every code
Shared heater or low-voltage codes change the first test.
- 03Inspect cold
Check for melted/chafed loom and terminal damage near hot exhaust.
- 04Test supply under load
Open-circuit voltage can hide resistance that collapses during heater current.
- 05Test element and PCM control
Use the exact model-year pinout and specification.
- 06Verify from cold soak
Confirm normal heater behavior and no pending P0135.
Do not buy a sensor before testing its feed and control, and do not substitute the downstream sensor. Never upsize a fuse. A manifold-mounted sensor and harness remain hot after shutdown.
Why the model year changes the test
CR-V diagnostics span the first-generation B20, K24-powered second through fourth generations, 1.5L turbo and 2.4L fifth-generation versions, newer 1.5L turbo models and 2.0L hybrid systems. AWD does not create another engine bank, but engine management, direct injection, turbo plumbing, EVAP packaging, VTEC oil hardware and hybrid operating modes change. Confirm the VIN, market, engine, build plant, emissions label and current Honda campaign status before selecting a flowchart or part.
- B20, K24, 1.5T and hybrid sensors differ in type, location and heater specification.
- The inline-four has one bank, but Sensor 1 versus Sensor 2 remains critical.
- Aftermarket universal wiring can introduce resistance or reversed connections.
- Use VIN/emissions calibration rather than thread size to select a sensor.
P0135 FAQ
Which sensor is B1S1?+
The upstream feedback sensor before the monitored catalyst.
Does P0135 prove the sensor signal is bad?+
No. It identifies the heater circuit.
Can I drive?+
Usually briefly if operation is normal and wiring/fuses are safe.
Can a fuse cause it?+
Yes, but determine why it opened.
Can I test resistance?+
Yes, with the exact Honda spec and correct heater terminals.
Why several heater codes?+
They may share a fuse, relay or supply branch.
Will a universal sensor work?+
It risks incorrect heater/signal characteristics.
What confirms repair?+
Normal cold-start heater current and no pending P0135.
Ford diagnostic references
These documents explain Ford monitor operation. Exact pinpoint tests, connector views and specifications must be selected for the truck's VIN and model year in current service information.
01Honda ServiceExpressHonda VIN-specific service information, DTC flowcharts, wiring and service publications↗02Honda Owners — CR-V manualsOfficial model-year warnings, fuel, maintenance and operating information↗