What Does P1191 Mean?
The downstream oxygen sensor heater circuit has an open condition preventing current flow. The sensor cannot reach operating temperature, affecting catalyst monitoring accuracy.
Common Causes
40%
Open circuit in heater element within oxygen sensor
30%
Broken or disconnected wire in oxygen sensor heater circuit
15%
Blown fuse for oxygen sensor heater circuit
10%
Failed oxygen sensor heater relay
5%
Corroded or loose connector at oxygen sensor or ECU
Diagnostic Steps
1
Step 1: Check oxygen sensor heater fuse and relay for proper operation
2
Step 2: Disconnect downstream oxygen sensor and measure heater element resistance (should show continuity, typically 3-30 ohms)
3
Step 3: Check for battery voltage at heater power supply wire with key on
4
Step 4: Verify ground circuit continuity from sensor connector to ECU or ground point
5
Step 5: If wiring and power are good but sensor shows infinite resistance, replace oxygen sensor
Estimated Repair Cost
$100 - $400
Parts + labor, varies by vehicle and location
The downstream oxygen sensor heater circuit has an open condition preventing current flow. The sensor cannot reach operating temperature, affecting catalyst monitoring accuracy.
The most common cause of P1191 (Oxygen Sensor Heater Circuit Open Downstream) is: Open circuit in heater element within oxygen sensor
Typical repair costs for P1191 range from $100 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive but catalyst monitoring will be disabled, potentially masking catalyst deterioration and increasing emissions.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1191 to identify the root cause.
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Quick Info
Category
Powertrain
System
Emissions Control
Difficulty
Type
Manufacturer
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