P1105

Code

PORSCHE P — Powertrain

Heating of HO2S 1 behind TWC

Brand: PORSCHE

Type: P — Powertrain

Views: UK: 3 EN: 4 RU: 6

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Page language: EN

Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
Possible inability to complete catalyst monitoring / failed readiness
Failed emissions test due to incomplete OBD readiness
Usually no noticeable driveability loss (downstream sensor heater commonly does not control fuel trim)

Retrieve freeze frame and live data; confirm bank and sensor number, and whether heater status is reported as fault
Check for related DTCs (upstream sensor, other heater circuit codes, P0420/P0430)
Inspect sensor wiring and connector for corrosion, damage, heat exposure or water ingress
Check fuses/relays supplying O2 sensor heaters
Measure battery voltage with ignition ON (heater supply should be near battery voltage)
Measure resistance of the sensor heater (with sensor disconnected and engine cool)

Heater cold resistance: typically a few ohms (varies by sensor; commonly ~2–20 Ω). Refer to manufacturer spec for exact value.
Supply voltage to heater: approximately battery voltage (~11–14 V) when powered
ECM may switch ground or use a PWM to modulate heater current; expect pulsed control rather than steady DC
Heater current draw: low amperage (typically under 5 A) — high current indicates short, zero/very high resistance indicates open circuit
Downstream O2 voltage signal (sensor output) is not used for closed loop fuel control but should be present once sensor is hot

Verify freeze frame and read all DTCs. Note ignition state and conditions when fault set.
Visually inspect the downstream O2 sensor (Bank 1 sensor 2) connector and harness for corrosion, damage, chafing, or heat damage. Repair any obvious issues.
Check related fuses/relays for O2 heater circuits; replace if blown and investigate cause.
With ignition OFF, disconnect the sensor connector. Measure heater element resistance across heater terminals; compare to manufacturer specification. Infinite/very high resistance = open heater. Very low/near zero = short.
With connector connected and ignition ON (engine OFF), backprobe the heater supply pin to verify battery voltage is present or present as expected by the vehicle design.
Backprobe the heater control pin while cranking or with engine running (as required) to verify ECM is switching/grounding the circuit (look for pulsed waveform with an oscilloscope or duty/voltage changes with a DVOM if applicable).
If wiring and power are good but heater element resistance is out of spec, replace the downstream O2 sensor.
If sensor heater is within spec but supply/control are absent or ECM output is not switching, inspect wiring for hidden damage and repair. If wiring is good, consider ECM/PCM as potential fault and consult manufacturer service information before replacement.
After repairs, clear codes and confirm that the MIL does not return and that OBD readiness tests complete for catalyst monitoring.

⚠️ Status

Heater circuit malfunction detected for heated oxygen sensor located downstream of the three‑way catalyst on Bank 1 (HO2S 1 behind TWC).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours

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P1105 — Heating of HO2S 1 behind TWC