P0135
O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)P0135 is a generic OBD-II powertrain diagnostic trouble code: O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1). It is logged by the engine control unit when the o2/lambda monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0135 means
DTC P0135 is a SAE generic powertrain code that indicates a malfunction in the heater control circuit of the oxygen sensor located on Bank 1, Sensor 1 — the upstream (pre-catalytic converter) O2 sensor on the same side of the engine as cylinder number one. The Engine Control Module (ECM/PCM) monitors the sensor's heater circuit and sets this code when the heater element fails to bring the sensor up to its operating temperature within an expected time window, based on inputs such as coolant temperature and ambient conditions at startup.
Modern heated oxygen sensors (HO2S) incorporate an internal resistance heating element that accelerates warm-up from cold starts, allowing the sensor to begin generating accurate voltage signals within seconds rather than waiting for exhaust heat alone. When this heater circuit is open, shorted, or drawing current outside the PCM's expected range, closed-loop fuel control is delayed or degraded. This means the ECM must rely on open-loop fuelling maps for longer than normal, which can increase fuel consumption and exhaust emissions.
P0135 is closely related to P0141 (Bank 1 Sensor 2), P0155 (Bank 2 Sensor 1), and P0161 (Bank 2 Sensor 2), all of which describe the same heater circuit fault on their respective sensors. The fault is generally moderate in severity: the vehicle remains drivable, but the MIL illuminates, emissions tests will fail, and a prolonged fault can mask additional problems or degrade catalytic converter efficiency over time.
Common causes
Most-frequently reported root causes when P0135 is logged.
-
1
Failed or open internal heater element inside the O2 sensor
-
2
Blown fuse in the O2 sensor heater supply circuit
-
3
Open or short circuit in the heater power or ground wiring
-
4
Corroded, damaged, or loose O2 sensor connector/harness
-
5
High resistance in the heater circuit due to chafed or heat-damaged wiring
-
6
Poor engine ground connection affecting sensor circuit reference
-
7
Internal short within the O2 sensor causing excessive current draw
-
8
Faulty ECM/PCM heater circuit driver (rare)
Symptoms drivers notice
How to diagnose P0135
A typical diagnostic flow when this code is present.
-
1
Connect a scan tool, read all stored DTCs, and note freeze-frame data to confirm P0135 is active and to check for related codes (P0131, P0141, etc.)
-
2
Inspect the O2 sensor wiring harness and connector on Bank 1 Sensor 1 for heat damage, chafing, corrosion, or water intrusion; repair any visible damage before proceeding
-
3
Locate and inspect the heater circuit fuse (refer to vehicle-specific fuse diagram); replace if blown and retest
-
4
With the sensor unplugged, use a multimeter to verify battery voltage (approximately 12 V) on the heater supply pin and a clean ground on the ground pin — both measured at the harness side, not the sensor
-
5
With the sensor unplugged, measure the heater element resistance across the two heater pins on the sensor itself; compare to manufacturer spec (typically 2–30 Ω depending on sensor type); an OL reading indicates an open element — replace the sensor
-
6
Check engine ground straps for looseness or corrosion and repair as needed, then clear the code and run a cold-start drive cycle to confirm the fault does not return
-
7
If wiring, fuses, and grounds all test good and the code persists after sensor replacement, suspect an ECM heater driver fault and consult vehicle-specific diagnostics
Vehicles where we've handled P0135
Platforms in our catalogue with confirmed P0135 coverage.
Related powertrain codes
- P0040 — Upstream Oxygen Sensors Swapped From Bank To Bank
- P0041 — Downstream Oxygen Sensors Swapped From Bank To Bank
- P0130 — O2 Sensor Circuit Malfunction (Bank 1 Sensor 1)
- P0131 — O2 Sensor Circuit Low Voltage (Bank 1 Sensor I)
- P0132 — O2 Sensor Circuit High Voltage (Bank 1 Sensor 1)
- P0133 — O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)
Frequently asked questions
Can I drive my vehicle with a P0135 code?
Yes, the vehicle is generally safe to drive short-term as P0135 does not typically cause limp mode or stalling. However, fuel economy may suffer and the MIL will remain on, which can mask other faults. Repair should be completed at the earliest opportunity.
Will P0135 cause me to fail an emissions test?
Yes. An active MIL or a pending P0135 code will cause an automatic failure on OBD-II emissions inspections (MOT, smog check, etc.) regardless of whether exhaust gas values are within limits.
Is the O2 sensor itself always the cause of P0135?
Not always. A blown fuse, damaged wiring harness, corroded connector, or poor ground connection can all trigger P0135 without the sensor being faulty. Always check fuses, wiring, and grounds before replacing the sensor to avoid an unnecessary part expense.
What is the difference between P0135 and P0130?
P0130 indicates the O2 sensor signal voltage on Bank 1 Sensor 1 is out of range (the sensor itself is not responding correctly), whereas P0135 specifically faults the heater circuit that warms the sensor up. The sensor element and the heater element are separate circuits inside the same sensor body.
Disabling P0135 in software
RaceTune can permanently disable P0135 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
ECUs with a P0135 disable in our catalogue
Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.
- Bosch EDC17C50 verified 1 software version
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
Got P0135 in your scan?
Upload your ECU file — we'll identify the exact software version and confirm whether a disable is available for your car.
Upload your file