Failed oxygen sensor heater element inside the downstream sensor on bank 1 or bank 2; Corroded, burnt, or disconnected wiring or connector pins at the sensor or harness; Blown fuse that supplies power to the oxygen sensor heater circuit; Open or shorted wire in the harness between the sensor and the engine control module; Faulty engine control module driver for the heater circuit, though this is less common; Oil or coolant contamination that has damaged the sensor's internal heater

DTC codes / Volkswagen codes / P1135

P1135 · VolkswagenOxygen Sensor Heating Circuit Bank 1 + 2 Sensor 2 Electrical Malfunction

P1135 on Volkswagen vehicles indicates that the engine control module has detected an electrical fault in the heater circuit for the downstream oxygen sensor on both banks of a V-style engine. The computer monitors the current flow through the sensor's heating element and flags this code when the circuit is open, shorted, or drawing current outside the expected range.

SystemPowertrain

Code typeVolkswagen specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Slightly higher fuel consumption during cold starts because the sensor takes longer to reach operating temperature
Occasional rough idle or hesitation when the engine is cold
A pending or stored fault that may cause the vehicle to fail an emissions inspection
In rare cases, a slight decrease in fuel economy over time if the sensor remains cold and the system stays in open loop longer

Common causes, most likely first

Failed oxygen sensor heater element inside the downstream sensor on bank 1 or bank 2
Corroded, burnt, or disconnected wiring or connector pins at the sensor or harness
Blown fuse that supplies power to the oxygen sensor heater circuit
Open or shorted wire in the harness between the sensor and the engine control module
Faulty engine control module driver for the heater circuit, though this is less common
Oil or coolant contamination that has damaged the sensor's internal heater

How to diagnose and fix it

Check the fuse that protects the oxygen sensor heater circuit and replace it if blown
Inspect the sensor connectors and harness for corrosion, chafing, or loose pins, and repair as needed
Measure the resistance of the heater element in both downstream sensors and compare to the manufacturer's specification
Test for power and ground at the sensor connector with the key on to confirm the circuit is complete
If resistance is out of spec or the circuit tests faulty, replace the affected oxygen sensor
Clear the fault codes and perform a road test to verify the repair and ensure the code does not return

What the heater circuit test really reveals

A P1135 can be set by a heater circuit that is electrically intact but drawing slightly too much or too little current, so a simple continuity check may not find the fault.
Volkswagen often groups both downstream sensors under one code, so technicians must check both banks even if only one sensor is suspected.
The downstream sensor heater is powered through a fuse that also supplies other components, so a blown fuse may cause additional codes that point away from the oxygen sensor.
Aftermarket sensors with incorrect heater resistance are a common cause of repeat P1135 codes even when the original sensor was replaced.
The engine control module may set this code intermittently if the heater circuit is affected by vibration or temperature changes, so a wiggle test of the harness is essential.

Can I keep driving with P1135?

You can usually continue driving with this code because the engine will still run, but the vehicle may fail an emissions test and cold-start fuel economy will suffer. Avoid long periods of idling from cold and have the fault repaired soon to prevent damage to the catalytic converter from unburned fuel.

Tools that help

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Guidance is general and written for Volkswagen vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.