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DTC codes / Jaguar codes / P1191

P1191 · JaguarO2 Sensor Heater Circuit Open, HArdware Fault

P1191 on a Jaguar indicates that the engine control module (ECM) has detected an open circuit or internal hardware fault in the oxygen sensor heater circuit, typically for a specific bank. The heater is responsible for bringing the sensor up to operating temperature quickly, and an open circuit means the ECM sees no current flow when it commands the heater on.

SystemPowertrain
Code typeJaguar specific
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms.
  • Extended warm-up period before the engine runs smoothly, especially in cold weather.
  • Slightly higher fuel consumption during the first few minutes of driving.
  • Intermittent rough idle or hesitation when the engine is cold.
  • Failed emissions test due to the heater monitor not completing.
  • In rare cases, a stored pending code without the light if the fault is intermittent.

Common causes, most likely first

  1. Failed oxygen sensor heater element (open circuit inside the sensor).
  2. Damaged or corroded wiring between the ECM and the oxygen sensor heater circuit.
  3. Blown fuse or faulty relay supplying power to the oxygen sensor heater.
  4. Poor electrical connection at the oxygen sensor or ECM connector.
  5. Internal hardware fault within the ECM driver for the heater circuit.
  6. Aftermarket oxygen sensor with incorrect heater resistance.
  7. Rodent damage or chafed wiring harness causing an open circuit.

How to diagnose and fix it

  1. Check the fuse and relay for the oxygen sensor heater circuit and replace if faulty.
  2. Inspect the oxygen sensor connector and wiring for corrosion, damage, or loose pins.
  3. Measure the resistance of the oxygen sensor heater element with a multimeter and compare to specification.
  4. Perform a voltage drop test on the heater circuit while commanding the heater on with a scan tool.
  5. Check for continuity between the ECM and sensor connector to rule out an open in the harness.
  6. If all wiring and fuses are good, replace the oxygen sensor with a quality OEM or equivalent part.
  7. If the fault persists after sensor replacement, diagnose the ECM driver circuit or replace the ECM as a last resort.

Don't overlook the heater fuse and relay

  • A blown fuse for the oxygen sensor heater is often caused by a shorted sensor or wiring, so replacing the fuse without finding the root cause will lead to a repeat failure.
  • The ECM may set P1191 even if the sensor heater is functional but the circuit has high resistance due to corroded terminals, which can mimic an open circuit.
  • On some Jaguar models, the oxygen sensor heater circuit is shared with other components, so a fault in a related system can trigger this code.
  • A scan tool that can read live data for heater current and voltage is invaluable for confirming whether the ECM is commanding the heater on and whether current is flowing.
  • After replacing the sensor, clear the code and perform a drive cycle to complete the heater monitor; otherwise the code may reappear as pending.

Can I keep driving with P1191?

You can generally continue driving with this code, but avoid extended idling and cold-weather short trips until repaired, as the engine may run richer during warm-up and emissions will be affected. If the check engine light flashes or drivability issues appear, stop driving and seek service.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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

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