P0030 P0xxx · Powertrain (P) Medium severity
HO2S Heater Control Circuit (Bank 1 Sensor 1)
The upstream oxygen sensor's internal heater is not drawing the expected current. The sensor then warms slowly, so fuel control stays open-loop longer and emissions and consumption rise.
Severity guidance: Medium — drivability or emissions affected, book it in this week
Symptoms you will notice
- Higher fuel consumption
- Rich or lean fuel trims
- Failed emissions test
- Rotten-egg smell
Common causes
Ordered from most to least likely — start at the top.
- 1 Burnt-out heater element inside the sensor (most common)
- 2 Blown heater fuse or open wiring
- 3 Corroded connector near the exhaust
- 4 Aftermarket sensor with wrong resistance
How to diagnose it
Cheapest and least invasive first — most of these codes are not a parts problem.
- ✓ Check the heater fuse first — a lot of these are a 15 A fuse.
- ✓ Measure heater resistance across the two same-coloured wires at the sensor connector.
- ✓ Confirm battery voltage reaches the harness side with the key on.
- ✓ Watch O2 sensor warm-up time in live data; a dead heater never reaches closed loop quickly.
Repair options
- Replace the oxygen sensor
- Repair wiring or connector
- Replace the heater fuse and find why it blew
P0030 — frequently asked questions
Can I just replace the fuse? +
If it blows again the heater or wiring is shorted. Find the cause before throwing fuses at it.
Does it affect the catalytic converter? +
Yes — prolonged rich running overheats and eventually destroys the catalyst.
Confirm the diagnosis before you buy parts
Send us the code, freeze-frame data and the vehicle — our engineers will tell you what to test first.