Which Codes Will This Page Cover?
- P0136 O2 Sensor Circuit – Bank 1 Sensor 2
- P0137 O2 Sensor Circuit Low Voltage
- P0138 O2 Sensor Circuit High Voltage
- P0139 O2 Sensor Circuit Slow Response
- P0140 O2 Sensor Circuit no Activity Detected
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What Is the P0136 Code?
Symptoms
Causes
Seriousness
Can I Still Drive?
Diagnose
Difficulty of Inspecting
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A P0136 code relates to the oxygen sensor 2 which lies post the catalytic converter and monitors the catalytic converter for the bank 1 side of the engine. It gathers voltage readings based on the oxygen level in the exhaust and relays it to the Engine Control Module (ECM), which uses it to regulate your engine’s fuel injection levels. Whenever the P0136 code appears, the ECM has determined that Sensor 2 located behind your car’s catalytic converter is malfunctioning.
Sensor 2 on the Bank 1 side means that it is located on the side of the engine that contains the #1 cylinder. The sensor 1 is tasked with reading the amount of oxygen in the exhaust system and then emitting a voltage measurement between 0.1 and 0.9 volts. It monitors these voltage readings and determines if the exhaust is lean – meaning there is more oxygen than expected – or rich – meaning that there is more fuel than air present. The ECM then increases or decreases fuel injector pulse width according to the air-to-fuel ratio that is set on the vehicle from the factory. It sets the P0136 code when the sensor 2 voltage is low for longer than two minutes. The wave form produced by the secondary O2 is much more gradual with a lower frequency bounce between 300 – 750 mv. The ECM will set codes P0139 or P0140 if it detects a slow response or no response from the O2 sensor, respectively. The P0138 code is set when the ECM detects a higher than average voltage reading (usually about 1.2 volts).
You may also be interested in:
P013C O2 Sensor Slow Response – Rich to Lean Bank 2 Sensor 2
P013E O2 Sensor Delayed Response – Rich to Lean Bank 1 Sensor 2
More About P0136 And Its Related Codes
As we mentioned, the P0136 code signifies the oxygen sensor that is located downstream from the engine, or behind the catalytic converter. These sensors operate with heaters that help the sensors get warmed up to operating temperatures quicker than they otherwise would by relying on the heat being emitted from the exhaust system. This is crucial to the sensor operating efficiently because the sensor needs to warm up so that the ECM can help the engine reach closed-loop operation. Under closed-loop operation, the engine will receive cues from the ECM as to the specific air/fuel ratio needed to operate efficiently.
The ECM continuously monitors the oxygen sensor’s voltage and determines if the exhaust is running lean or rich and will continue to adjust the fuel injection system to make sure that the engine’s air-to-fuel ratio is optimal for peak performance. While the primary sensor is tasked with adjusting fuel trim, the secondary O2 sensor is monitoring the catalyst’s performance during this time and the readings from Sensor 2 are vital in this operation. So the P0136 and its related codes can also be tied to the catalytic converter and its performance and is why they are important codes to note and know about.
What Are the Symptoms of a P0136 Code?
One of the first symptoms of the P0136 code is that you will notice your vehicle triggers the Check Engine Light on your dash. Usually, you won’t notice immediate physical symptoms once the light comes on but that’s not to say that symptoms don’t arise with this code. One of these symptoms is that your engine may start running excessively rich if it is not able to get out of open-loop mode. As we stated before, the closed-loop mode is when the engine can take in commands from the ECM on how much air and fuel to use. In turn, the open-loop mode is the converse of the closed-loop mode. This means that the engine is operating with an air/fuel ratio that is not defined by any inputs from the ECM and is highly inefficient to its performance. This will usually lead to your engine misfiring if the spark plugs get fouled out from the extended and excessive use caused by the prolonged open-loop mode. Another symptom is that your exhaust may be leaking and losing power, so you may notice a rough idle or a lack of ability of your car to efficiently accelerate.
What Are Some Causes of a P0136 Code?
One of the most common causes of a P0136 code setting, or any of its related codes setting, is simply a faulty oxygen sensor or a leak in the exhaust portion that is close to the sensor. Another possible cause is that the oxygen sensor circuit is shorting out because of corrosion in the sensor connector or wiring harness surrounding the sensor. These conditions will cause a short in the circuit or the circuit resistance to be open. Often the condition of the wiring to the sensor or from the sensor to the PCM is the cause of the P0136 code setting.
How Serious Is the P0136 Code?
The P0136 code and its related codes can become serious issues in that they can point to exhaust problems causing the O2 sensor to give erratic output voltages. The sensor also may not read correct measurements if the catalyst is damaged in front of the sensor. Also, if the engine stays in open-loop mode for extended periods of time this can cause significant damage to the engine internals, like pistons and valves. This all points to high repair bills that can be avoided and is why the P0136 can be considered a serious code.
Can I Still Drive with a P0136 Code?
While the P0136 won’t lock up your engine immediately or cause symptoms that prevent you from operating your vehicle, we still don’t recommend that you drive with the code present. You should take your car to a certified service center when you see the P0136 or its related codes so that it can be immediately diagnosed and fixed. You don’t want to potentially cause more damage to your engine than is needed by forcing it to operate with the wrong air and fuel ratios. This puts unnecessary pressure on your engine internals and can lead to very high repair bills.
How Easy Is It to Diagnose a P0136 Code?
Since the P0136 code can lead to further and more significant engine issues, we recommend that you allow qualified technicians to diagnose and inspect your vehicle. What a technician will first do is monitor the vehicle’s oxygen sensor freeze frame data to verify the problem and confirm that the voltage is low. They will then physically inspect the sensor’s wiring and connectors, as well as the wiring harness, for evidence of damage or corrosion. It’s also important to note that you should check for any contaminants on the sensor, like oil or coolant from the engine, that may be caused by engine leaks. Also, checking the O2 sensor’s heater circuit is important because the resistance should be to the vehicle’s factory specifications. They will also check the catalyst in front of the oxygen sensor to see if it’s damaged, while also checking for exhaust leaks around the sensor.
How Difficult Is It to Inspect a P0136 Code?
Because the inspection process for a P0136 involves multiple steps and a variety of vehicle systems, we don’t recommend that you try and perform this process yourself. This is best left to qualified technicians with the required prior experience dealing with these sorts of issues. With that said, what a technician will do to repair the issue is replace the sensor if that is what’s needed. They may also repair or replace the wiring or connectors surrounding Sensor 2 if that is found to be the issue. They will also repair any exhaust leaks first before addressing the sensor. This process requires tools like voltage meters and advanced scanners and is best left to technicians that have experience using these tools.
Need Additional Help with Your P0136 Code?
While the P0136 can be considered moderate in nature, it shouldn’t have to be. Following the information our experts provided you should be able to have your car running in peak condition as long as you know when to take your vehicle to a service center.
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