AutoFixDB - Free OBD-II diagnostic trouble code lookup. Find causes, symptoms, diagnostic steps and repair solutions.

Overview

P0135 indicates a malfunction in the heater circuit of the Bank 1 Sensor 1 oxygen sensor; causes include failed heater element, wiring/circuit faults, blown fuse, or rare ECU driver failure. Diagnosis includes scan tool, visual and electrical tests (voltage/resistance). Typical repair: fix wiring or replace sensor.

Common Symptoms

Check Engine Light illuminated
Reduced fuel economy
Rough idle during cold start
Delayed closed‑loop operation

Most Common Causes

Heater element failure inside the oxygen sensor high

Internal heater open or short causes ECM to detect insufficient heating

High resistance or open/short in heater circuit wiring/connectors high

Corroded, damaged, or loose wiring interrupts heater circuit

Blown fuse supplying the O2 heater circuit medium

Fuse protecting heater power can open, cutting power

ECU/PCM heater driver circuit malfunction low

Rare failure of ECU driver can lead to circuit not being energized

Diagnostic Steps

Confirm presence of P0135 using an OBD‑II scanner and note freeze frame data

Expected: P0135 stored; no other conflicting codes

Interpretation: Verifies heater circuit fault before further diagnosis
Perform visual inspection of Bank 1 Sensor 1 harness and connector

Expected: No frayed wires, corrosion, or loose connections

Interpretation: Damaged wiring/connectors likely if abnormalities are found
Test fuse for heater circuit continuity

Expected: Fuse intact

Interpretation: Blown fuse indicates circuit protection action
Measure resistance of oxygen sensor heater element with multimeter

Expected: Resistance within manufacturer spec (varies by vehicle)

Interpretation: Open or out‑of‑range resistance suggests failed heater
Verify voltage supply from ECU to heater circuit with ignition on

Expected: Proper 12 V supply and good ground

Interpretation: Lack of voltage/ground indicates wiring or ECU driver issue

Repair Solutions

Repair/replace damaged wiring or connectors medium

Estimated Cost: $20 - $150

Depends on extent of wiring damage

Replace oxygen sensor (Bank 1 Sensor 1) easy

Estimated Cost: $80 - $350

Sensor replacement often resolves heater circuit faults

Replace blown fuse easy

Estimated Cost: $1 - $10

Check for underlying short before replacing

Repair or reflash faulty ECU/PCM hard

Estimated Cost: $200 - $800

Rare and usually last‑resort after confirming other causes

Common Misdiagnoses

Avoid these common diagnostic mistakes:

Assuming general O2 sensor failure without checking heater circuit wiring first
Misidentifying related O2 sensor codes (e.g., P0141 or P0155) as P0135

Frequently Asked Questions

What does the P0135 code mean?

Technically, the P0135 code represents Oxygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1). It usually points to a fault within the Sensors.

Is it safe to drive with a P0135 code?

You should treat P0135 as a medium issue. Sets Check Engine Light; may cause extended open‑loop operation, reduced fuel economy, rough idle mainly on cold start

What are the symptoms of P0135?

You may experience the following: Check Engine Light illuminated, Reduced fuel economy, Rough idle during cold start.

Why is my car throwing a P0135 code?

Potential culprits include: Heater element failure inside the oxygen sensor, High resistance or open/short in heater circuit wiring/connectors, Blown fuse supplying the O2 heater circuit. A proper diagnosis is recommended.

Repair cost breakdown for P0135

Repair costs depend on the specific failure. A simple Replace blown fuse replacement is relatively affordable ($1-$10), whereas a Repair or reflash faulty ECU/PCM repair is more expensive, potentially reaching $800.

Does P0135 affect Ford, Toyota, or Honda?

The P0135 code is a generic powertrain code, meaning it applies to almost all makes and models, such as Honda, Toyota, VW, Ford, and Chevy.

P0135: Oxygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)