P0135: O2 Sensor Heater Circuit — Bank 1 Sensor 1
What to do
No urgent driveability impact. Closed-loop fuelling is delayed after every cold start, so economy suffers on short trips and it will fail an emissions test.
What this code means
A fault in the heater circuit of the upstream bank 1 sensor. This overlaps in meaning with P0030 — different modules favour different codes for the same condition, and some store both. Practically they are diagnosed identically: check the fuse, the connector, and the heater element's resistance across its dedicated pins.
Likely causes
Start here
Less common
- Open circuit in heater wiring · moderate
- Exhaust heat damage to sensor harness · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
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