P0135

Code

Generic P — Powertrain

O2 Sensor Heater Circuit Bank 1 Sensor 1

Brand: Generic

Type: P — Powertrain

Views: UK: 58 EN: 62 RU: 187

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Page language: EN

Causes

Open or short in the heater circuit wiring
Blown fuse or bad relay supplying heater power
Failed O2 sensor heater element
Corroded or loose connector/terminals
ECM/PCM driver fault

Symptoms

Check Engine Light (MIL) illuminated
Failed emissions test or high HC/CO readings
Poor fuel economy or unstable fuel trims, especially on cold start
Rough idle or increased warm-up time
Possible hard starting when engine cold

What to check

Read and record freeze frame and live PID data with a scan tool; confirm P0135 and related codes
Visual inspection of sensor, wiring, and connector for damage, corrosion, or contamination
Check fuse(s) and relays that supply heater power
Measure voltage at the sensor connector (battery voltage on heater supply with key ON)
Measure resistance of the heater element at the sensor (with sensor disconnected)
Backprobe control/driver side to verify ECM switching/grounding when commanded (use scan tool to command heater ON if supported)

Signal parameters

Heater element resistance (approx): typically 2–15 ohms (varies by vehicle and sensor type) — consult vehicle spec
Supply voltage: battery voltage (~11–14 V) present on the heater power feed with key ON (fused)
Control signal: ECM typically switches the other heater terminal to ground (verify switching with scope or DVOM while commanding heater)
Current draw (approx): 0.5–2 A when heater powered (depends on resistance and voltage)
Warm-up time: heater should reach operating temp quickly (often within a few seconds to a minute depending on design)

Diagnostic algorithm

Verify P0135 stored and note any related codes (other O2 heater or sensor codes).
Perform a visual inspection of Bank 1 Sensor 1, connector, and wiring for obvious damage, contamination, or corrosion. Repair as needed.
Check relevant fuses/relays for the heater power feed; replace any blown fuses and retest.
With the sensor disconnected, measure heater resistance across the heater pins. Compare to vehicle specification. An open or infinite reading indicates a failed heater.
With key ON (engine OFF), verify battery voltage at the heater power pin of the sensor connector. If absent, trace back to fuse/relay/power feed.
Command the heater ON with a scan tool (if supported) and backprobe the control pin to verify the ECM is switching/grounding the circuit. If the ECM does not command, confirm scan tool capabilities and inputs.
If the supply and control signals are correct but heater resistance is open/short, replace the O2 sensor.
If supply is missing or intermittent, trace and repair wiring (replace damaged harness, clean/replace connector) and retest.
If supply and wiring are good but control side not switching, suspect ECM driver fault—verify with manufacturer procedures before ECM replacement.
After repair, clear codes and perform drive cycle to confirm P0135 does not return and the heater reaches operating condition.

Likely causes

Broken or chafed heater supply wire near the sensor
Failed sensor (internal heater open or shorted)
Blown fuse for sensor heaters or related power feed
Corroded sensor connector (pin corrosion, water intrusion)
Control side open/short to ground due to damaged harness
ECM driver transistor failure (less common)

Fault status

⚠️ Status

P0135 - O2 Sensor Heater Circuit Bank 1 Sensor 1: Heater circuit fault (open, short, or control failure) preventing the upstream O2 sensor from reaching operating temperature.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours