What Does P1158 Mean?
This code indicates the downstream heated oxygen sensor (HO2S) on bank 2 is stuck indicating a rich exhaust condition and is not switching properly. The post-catalyst sensor is reading a consistently high voltage (above 0.6V) without the expected stable plateau, or it is fixed at a rich reading. This can indicate a sensor fault, a saturated catalyst on bank 2, or a persistent rich running condition that the fuel system cannot correct.
Common Causes
30%
Failed downstream HO2S on bank 2 (internally biased rich or contaminated with silicone/coolant)
25%
Catalytic converter on bank 2 saturated with unburned hydrocarbons or failing
20%
Persistent rich fuel condition on bank 2 (leaking injector, high fuel pressure)
15%
Sensor wiring shorted to voltage source or damaged connector
10%
Coolant leak into combustion chamber contaminating the sensor (head gasket issue)
Diagnostic Steps
1
Monitor bank 2 downstream HO2S voltage in live data; verify if the reading is fixed above 0.7V or showing minimal switching.
2
Check bank 2 upstream fuel trims; large negative LTFT values indicate the PCM is compensating for a persistent rich condition.
3
Create a controlled lean condition (briefly remove a vacuum hose) and verify the downstream sensor voltage drops in response; a non-responsive sensor is faulty.
4
Inspect for signs of coolant consumption (white exhaust smoke, coolant loss, fouled spark plugs) which could contaminate both the catalyst and sensor.
5
If fuel trims are normal and the sensor does not respond to lean conditions, replace the bank 2 downstream HO2S.
Estimated Repair Cost
$120 - $450
Parts + labor, varies by vehicle and location
This code indicates the downstream heated oxygen sensor (HO2S) on bank 2 is stuck indicating a rich exhaust condition and is not switching properly. The post-catalyst sensor is reading a consistently high voltage (above 0.6V) without the expected stable plateau, or it is fixed at a rich reading. Thi...
The most common cause of P1158 (Lack of Downstream Heated Oxygen Sensor Switch - Sensor Indicates Rich - Bank No. 2) is: Failed downstream HO2S on bank 2 (internally biased rich or contaminated with silicone/coolant)
Typical repair costs for P1158 range from $120 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
No immediate safety risk to occupants. A persistent rich condition can cause catalyst overheating over time, potentially increasing fire risk if the converter becomes extremely hot near undercarriage components.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1158 to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel / Air Metering (Catalyst Monitoring)
Difficulty
Type
Manufacturer
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