DTC P0135 (Diagnostic Trouble Code P0135) is defined as “O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)”.
It occurs when the Powertrain Control Module (PCM) or Engine Control Module (ECM) tests the oxygen sensor heater circuit in Bank 1 and detects a problem. Here, ‘Bank 1 Sensor 1’ refers to the upstream oxygen sensor located closest to the engine on the side with cylinder #1.
Without a functional oxygen sensor or heater element, the PCM or ECM won’t adjust the engine’s fuel injectors to maintain an air-fuel balance for each combustion cycle. As a result, the engine will run rich and affect your vehicle’s fuel efficiency.
This problem is more common in older vehicles and is typically triggered by a short circuit or excessive resistance in the heater circuit.
The P0135 code doesn’t have many obvious symptoms, but here’s what you may notice:
Yes, you can still drive with a P0135 code. However, it’s a moderately serious issue and is best addressed promptly.
A functional O2 sensor heater helps maintain efficiency and engine power. So, extended driving with this issue can lead to:
Here are a few instances that can cause code P0135:
Several issues could trigger engine code P0135 apart from a malfunctioning oxygen sensor heater circuit. This is why it’s important to properly diagnose the code and implement relevant repairs.
Here’s what a mechanic would do to diagnose the problem:
Note: This diagnosis helps identify the core of the problem before needlessly replacing any expensive parts, like the O2 sensor. For example, installing a new sensor won’t resolve wiring or harness connector issues.
Here are the steps your mechanic may take to address code P0135:
Note: The vehicle manual will have a circuit description and wiring diagram of the O2 heater circuit. A mechanic will refer to this guide while replacing the wiring, the heated oxygen sensor connector, and other circuit components.
Code P0135 can have several root causes, from wiring issues, a blown fuse, to a faulty heated oxygen sensor. So, the cost of the repairs depends on the action needed.
Depending on the mechanic’s labor rate, the diagnosis can cost around $75-$150. After the diagnosis, the mechanic will quote the repair cost.
Here’s a general estimate of the cost of some repairs and replacement parts:
Note: The repair cost can vary depending on your car’s make and model. And if the Check Engine Light still flashes after the above replacement and fixes, you should consider having the PCM or ECM checked.
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