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Error Code P0158 is defined as O2 Sensor Circuit High Voltage Bank 2 Sensor 2. This refers to a trouble in the Bank 2 Sensor 2 of the O2 (oxygen) sensor, which is located near the backside of the exhaust, behind the catalytic converter. The code is set when the PCM (powertrain control module, also known as ECM or engine control module in some makes) detects the voltage signal of the oxygen sensor has remained in high voltage for too long.
It’s a generic trouble code, meaning it appears in all vehicles equipped with OBD-II code, or vehicles made since 1996 to present. Specifications on the definition, troubleshooting and repair vary from one make/model to another.
This error code refers to the O2 sensor behind the catalytic converter, at the back side of the exhaust. The main function of this sensor is to regulate the amount of oxygen that gets inside the catalytic converter and sends that information to the PCM for the efficiency and the oxygen level released by the catalytic converter. Lean mixture of O2 and gas means there is too much oxygen in the exhaust, while rich mixture of O2 and gas means there is not enough oxygen in the exhaust.
The Oxygen sensor is made up of four wires; with the PCM providing reference/signal voltage of around 0.5V to the sensor, as well as ground for the two wires. These vary according to the O2 level content in the exhaust. The other two wires are for the heater element of the O2 sensor, and it works by allowing the sensor to warm up faster, and ultimately get the engine to enter closed loop faster, reducing startup emissions. This heater element is supplied (usually) with 12V feed from power distribution center and ground. Changes in the resistance affect the 0.5 V supplied by the PCM. It is capable of changing between 0.1V and 0.9V. The former indicates full lean, while the latter explains full rich. Changes in voltage are monitored by the PCM.
There should be a perfect balance in the mixture level of oxygen and gas, as neither lean nor rich is good for the catalytic converter as both can cause it to fail prematurely.
This code appears when the voltage on the signal circuit is higher than normal for a longer period of time specified by the PCM. Not though that, a post-catalyst oxygen sensor normally switches fewer times and slower than front pre-cat O2 sensors.
Check Engine light is the most obvious symptom for Error Code P0158, as it will not usually cause drivability issues, since it only suggests an input that measures the efficiency of the catalyst (unlike the front Oxygen sensors). However, there’s a good chance that other error codes may be present as well, such as lean condition codes or pre-O2 sensor codes, which may cause drivability issues, such as the Error Code P0143. For some cases with symptoms, the common symptoms will be:
- Engine performance problems
- Rough running
- Poor idle
- Engine dies
- Poor fuel efficiency
- Loss of power and misfires intermittently
- Engine running rich (happens when the PCM tries to compensate by adding fuel for low oxygen sensor voltage reading)
Potential causes of this error code are:
- Bad Oxygen sensor
- Exhaust holes causing the PCM to read over-rich which results to abnormally high reading in Bank 2 Sensor 2
- Wiring in close contact with exhaust components causing it to chaff or melt and exposed
- Engine running rich
- Short to voltage in signal circuit
- Bad PCM
How to Check
As with other trouble codes, mechanics diagnose this code with the help of an OBD-II scanner to get all present codes that have been stored to the PCM.
Also, the OBD scanner will show the live stream data of the O2 sensor, where the mechanics can use to check the voltage reading and see if the sensor switches from low to high voltage every few seconds.
When there is a trouble code that represents engine coolant temperature problem, the live data on the scanner will be checked for the engine’s temperature.
Then mechanics will check the wiring of the rear O2 sensor and look for signs of breaks, shorts and exposures.
They will then test the fuel pressure to see if it’s higher than normal.
In many cases, a manufacturer’s diagnosis is needed for the PCM to determine whether the problems should be repaired or simply needs an update.
How to Fix
As with most error codes that concerns the O2 sensor, repairs for this one is pretty straightforward, which include:
- Replacement of the rear O2 sensor
- Repair broken, exposed or shorted out O2 sensor wires
- Repair excessive fuel pressure
- Replace engine coolant temperature sensor, if necessary
- Replace or update the PCM, if necessary
Error Code P0158 is quite a serious trouble code that needs attention ASAP, as it causes drivability issues, such as stalling which can be dangerous when driving.
When conducting a repair for this error code, the O2 sensor set and propane tank are needed to remove the O2 sensor if it is difficult to reach or has ceased in the exhaust.