P0327 and P0322 codes: Diagnose and fix like a mechanic [how-to guide + videos]

P0327 CODE & P0332 CODE
Knock Sensor 1 Circuit Low Input (Bank 1 & Bank 2)

Is your Check Engine light on, and you have a code P0327 or P0332, but you don’t know what that means? 

Our mechanic explains what these “Knock Sensor Circuit Low Input” OBD2 codes mean, what can cause them, and shows you how to diagnose your car’s knock sensors by reading their signals and inspecting their wiring harnesses in this video. Watch now: 

Check Engine Light? Knock Sensor Low Input – Code P0327 P0332 

What are codes P0327 and P0332, and what do they mean? 

P0327, “Knock Sensor 1 Circuit Low Input (Bank 1),” and P0332, “Knock Sensor 1 Circuit Low Input (Bank 2),” usually mean your knock sensors are bad—they’re malfunctioning—and need to be replaced

P0327 Code
P0332 Code
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What is engine knock? 

During a vehicle’s combustion process, which you can read about in “How to diagnose a misfire: Expert help from our mechanics,” if a spark plug ignites the fuel too early, or if the fuel used in a vehicle is incorrect, that can create too much pressure inside the engine, which results in an internal explosion outside of the normal combustion process. This engine knock results in a knocking or tapping sound. 

The purpose of knock sensors is to monitor and alert your car’s computer, or the powertrain control module (PCM), if engine knocking occurs. 

How serious are P0327 and P0332—can I drive with these codes? 

If left unaddressed, engine knocking can damage your engine and lead to more costly repairs, so it’s best to resolve a P0327 or P0332 as soon as possible and avoid driving with it. 

What are typical P0327 and P0332 code symptoms? 

  • Your Check Engine light is on 
  • Drivability issues can include difficulty accelerating, unsteady RPM, or loss of engine power 
  • A knocking or tapping sound 

What causes a P0327 or P0332 code? 

  • Bad or faulty knock sensor 
  • Faulty, open, or shorted knock sensor circuit wiring 
  • Corroded knock sensor wire connector 

How do I diagnose and fix P0327 or P0332? 

In the video above, the knock sensors in the vehicle our mechanic works on are located under the intake, so he removes the intake to access them. 

Test your knock sensors’ data readings 

  • With the meter set to AC voltage for the range millivolts, put one of the leads on one of the knock sensors and ground the other lead.
  • Use a screwdriver to tap near the sensors and watch the meter reading while you do this. 
  • If the readings don’t change at all while you do this, that means the problem triggering a P0327 or 332 is an open circuit in the knock sensor. 
  • You can also check the knock sensor’s resistance with a multimeter (2:19). Set the meter to ohms (which looks like a little horseshoe), place one of the leads on the ground, and the other on one of the knock sensors. 
  • If your meter’s reading says, “OL,” that means there’s an open circuit in one of the sensors, which means that knock sensor isn’t working. 

Check your knock sensor wire connectors for corrosion 

  • If a knock sensor connector is corroded, you’ll need to replace both the sensor itself and the wire. 
  • After inspecting the knock sensors, our mechanic recommends replacing your wiring harness at the same time you replace other parts in this area, such as a bad knock sensor that needs to be replaced. Wiring harnesses aren’t expensive parts, which makes it worth replacing them since they become brittle over time. 

Mechanic tip: Be careful when replacing knock sensors because they’re sensitive—you don’t want to accidentally drop and damage them. 

How to Replace Knock Sensors

Once you’ve determined what triggered a P0327 or P0332 in your car, and replaced any bad parts, clear the code, and drive your car to make sure everything’s running correctly. 

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P0420 and P0430 codes: Diagnose and fix like a mechanic [how-to guide + videos]

P0420 Code
P0430 Code
Catalyst System Efficiency Below Threshold (Bank 1 & Bank 2)

So, your Check Engine light is on, and you’ve got either a P0420 or a P0430, “Catalyst system efficiency below threshold” OBD-II code that is triggered when your car’s computer (the powertrain or engine control module (PCM or ECM)) detects a catalytic converter issue. 

In this video, our mechanic explains how a catalytic converter’s efficiency is reduced when it’s clogged, which triggers one of these two error codes. Watch now: 

Check Engine Light? Catalyst System Efficiency Below Threshold – Code P0420, P0430 

You can watch more videos like this in our video library.

What are codes P0420 and P0430, and what do they mean? 

What are these “Catalyst system efficiency below threshold” codes, and how do they differ? Each code indicates where the problem triggering them is located: 

  • P0420, “Catalyst System Efficiency Below Threshold (Bank 1)” means the problem causing it is happening in Bank 1 (where your vehicle’s cylinder number 1 is located). 
  • P0430, “Catalyst System Efficiency Below Threshold (Bank 2)” means the issue triggering it is happening in Bank 2 (where your vehicle’s cylinder number 2 is located). 

According to our mechanic, “Generally, this code means that you need a new catalytic converter.” 

When your car’s catalytic converter is working correctly, it breaks down pollutants that result during the combustion process so that they’re less toxic and less are released by the time they’re emitted as exhaust. 

A code P0420 or P0430 means a catalytic converter isn’t performing as efficiently as it should. When this happens, it’s not able to break down all those harmful pollutants, and still releases them. 

In the video above, our mechanic shows us two catalytic converters—one that’s clogged, and one that isn’t. She explains that the clogged catalytic converter’s filter, often referred to as “honeycomb,” prevents the correct amount of air from getting through, which can trigger a P0420 or P0430. 

How serious are P0420 and P0430 codes—can I drive with them?

Usually, by the time you’re aware of one of these codes, it’s too late—the damage is done to your catalytic converter. If it isn’t replaced, it can get worse, becoming more plugged, which can cause weak acceleration. 

What are common P0420 and P0430 symptoms? 

  • Your Check Engine light is on 
  • Rough-running engine or lack of power 
  • Poor fuel economy 

What causes P0420 and P0430? 

The most common P0420 and P0430 cause is a clogged catalytic converter filter, which requires replacing the entire catalytic converter. 

Other causes can include: 

P0420
P0430
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Can a bad o2 sensor cause a P0420 code?

In this video, our mechanic explains how a bad o2 sensor can trigger a P0420 code.

Check Engine Light? Catalyst System Efficiency Or Bad O2 Sensor? – Code P0420/P0430 

Our mechanic Andy says that a bad o2 sensor, or one that’s reading incorrectly, can cause a P0420 or P0430. However, too much fuel from a leaky fuel injector could be what caused the o2 sensor to go bad in the first place. He said they can also sometimes get stuck. Even if it’s clear that your catalytic converter needs to be replaced because its filter is clogged, Andy says it may be best to replace your o2 sensors at the same time, rather than take a chance. 

If the downstream o2 sensor detects a limited amount of carbon dioxide, which means the catalytic converter isn’t able to effectively break down pollutants, she says that’s when a P0420 code is triggered. 

To learn more about the difference between downstream and upstream o2 sensors from one of our mechanics, watch this video: 

O2 Sensors is it Upstream or Downstream? 

How do I diagnose and fix P0420 and P0430? 

Our mechanic Andy says the reason the 2009 Chevy Malibu he works on in the video below has a P0420 code is that the two o2 sensors’ readings are off, and detect an issue in the catalytic converter. 

Watch the full video for his expert help diagnosing and resolving a code P0420: 

P0420 Check engine light how to fix it yourself 

Video from Andy The X Tech

Check your catalytic converter for leaks 

Andy recommends inspecting the back of your catalytic converter for leaks. That could cause a faulty reading from the downstream, or back, o2 sensor. 

Inspect your catalytic converter’s filter, or screen, for clogging 

Andy’s catalytic converter filter is plugged up, and he compares it to the one in a new catalytic converter, which doesn’t have anything obstructing it. 

Other items to check out 

Even though as Andy tells us, 99.9 percent of the time, a code P0420 or P0430 means you’ll need to replace your catalytic converter, he recommends checking out a few other items before replacing it: 

  • Make sure your engine is running properly. 
  • Check for any exhaust or intake leaks, including any that are past the MAF sensor, or for any other intake or MAF sensor problems. 
  • Make sure your spark plugs are in good shape and working right in order to avoid a misfire, which will only make matters worse by allowing fuel to get into the catalytic converter. If it looks like they could be causing the problem, replace them. 
  • Keep up on regular maintenance. This may sound obvious, but if you don’t properly maintain your car with regular oil and filter changes, your car is more likely to experience issues that trigger trouble codes like P0420 or 430. 
  • Inspect your o2 sensors. As Andy says in his video on P0420, it’s probably best to replace them at the same time you replace your catalytic converter if you know it’s clogged. 
  • If you have any other OBD-II codes, check those before replacing your catalytic converter! Catalytic converters are not cheap parts, so you should definitely check out any other codes your car has before buying one in case there’s actually something else causing the problem. 

How much does it cost to fix codes P0420 or P0430? 

Depending on your vehicle, catalytic converters can range from a low of about $110 to upwards of $1,000. And that doesn’t include labor costs if you’re planning to have it replaced by a mechanic. Combined part and labor prices can range from about $400 to upwards of $2,000. 

Depending on how many oxygen sensors you replace, the cost could be minimal, but you can find out how much it will cost for your year, make, and model on 1aauto.com. 

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P0141 code: How to diagnose and fix it [guide + video]

P0141 Code
02 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)

What does it mean if you have a P0141 code and your Check Engine light is on? P0141, “O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2),” means something is preventing your car’s Bank 1 number 2 o2 sensor’s heated circuit from working correctly.

In this video, our mechanic shows you how to inspect and test your oxygen sensors, their circuits and wiring, fuses, and other areas to help you figure out what’s triggering the P0141 code.

Watch now: 

Check Engine Light? O2 Sensor Heater Circuit Malfunction – Code P0141 

You can find more videos like this in our video library

What is code P0141 and what does it mean? 

When your car has a P0141 diagnostic trouble code, that means the heated circuit found in the downstream o2 sensor 2 in Bank 1 is malfunctioning. Our mechanic explains that heated circuit’s role beginning at :17 in the video above. 

That heated circuit isn’t heating up, which means the o2 sensor itself may be faulty or failing, or that its circuits, wiring, or connectors could be faulty or broken. A blown fuse or Powertrain Control Module (PCM) issue could also prevent the circuit from heating properly. 

Can I drive with P0141? How serious is this code? 

Depending on what’s causing the issue that triggered P0141, your engine may become stuck in “open loop” mode, which means more fuel is burned than usual. It’s best to address a P0141 code as soon as possible to avoid other related repairs. 

What are typical P0141 code symptoms? 

What are the common causes of P0141? 

  • Power circuit wiring issue or damage, such as a wiring break or something else preventing power from getting to the fuse box 
  • Blown fuse 
  • PCM circuit break or other wiring issue 
  • PCM issue 
  • Faulty or failing Bank 1, o2 Sensor 2 heated circuit 
  • Faulty or failing Bank 1, o2 Sensor 2 
  • Remote starter not sending power to the o2 sensor’s circuits 
P0141 Code
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How do I diagnose and fix code P0141? 

Inspect and run power circuit tests 

  1. Use a test light to check the fuse to determine if the issue is power-related 

You’ll want to turn your key to the on position (your car doesn’t have to be running). Use a test light to test both o2 sensor fuses (depending on your vehicle, these two fuses will be referred to as fuse 1 and fuse 2 or fuse A and fuse B). Our mechanic walks you through how to do this test at 1:44 in the video above. If the test light lights up, you’ll know that particular fuse isn’t causing the problem that triggered P0141. 

If the power circuit isn’t working, there could be a break in its wiring, or another issue preventing power from getting to the fuse box, or you could even have a blown fuse. 

  1. Inspect Bank 1, Sensor 2’s wires and connector for fraying or damage 

Our mechanic shows you how to locate your o2 sensors, and the Bank 1, o2 sensor 2 specifically, beginning at 2:17. The vehicle our mechanic works on in the video has four o2 sensors: Two on the driver’s side and two on the passenger side. The Bank 1 sensors are referred to as Bank 1, Sensor 1, and Bank 1, Sensor 2; the Bank 2 sensors: Bank 2, Sensor 1, and Bank 2, Sensor 2. 

Check Bank 1, Sensor 2’s wiring (2:59)—our mechanic notices some “chafing” on the outside part of one wire, but it doesn’t look like any of the wires are broken. 

Also, inspect this sensor’s electrical connector (3:12). Disconnect the connector and look at its terminals to see if they look like they’re spread apart or green, either of which indicates an issue. 

  1. Use a test light to check the fuse to determine if the issue is ground-related 

With your key still on, use a test light to test the ground (our mechanic shows you how to do this beginning at 3:29). 

Inspect and run PCM circuit tests 

Use a multimeter or test light to test the resistance 

As our mechanic explains at 4:11, you could test the ground circuit using a multimeter, but the results aren’t always as accurate as using a test light (4:21). 

If the test light doesn’t light up, this could mean that there’s a break in the wiring, or that something is wrong internally in the PCM. 

If both circuits are working, then it’s the oxygen sensor’s heated circuit that’s causing the problem and triggering the P0141 code, which means you’ll need to replace that o2 sensor. 

In a case when your car has all four heater circuit control codes (list them here), you probably don’t need to replace all four o2 sensors. It’s more likely that something else is causing the problem, such as an aftermarket remote starter not powering the circuits that turn on the controls. 

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P2138 code: Diagnose and fix it like a mechanic [how-to guide + video]

p2138 code
Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation

Your Check Engine light is on and you’ve got a code P2138, “Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation.” What does that mean? In this video, our mechanic breaks down the P2138 code, its symptoms, including poor acceleration and reduced power mode, and shows you how to diagnose the potential causes so you know what to do to clear the code.

Watch now: 

Check Engine Light? Weak Acceleration or Reduced Power – Code P2138 

Want to watch more videos like this? Visit our video library for thousands of automotive diagnostic and how-to videos.

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P0300 code: Mechanic advice to diagnose and fix

Our mechanic shows you how to diagnose and fix the problem causing a P0300 code (“Random/Multiple Cylinder Misfire Detected”), and uses an OBD2 scan tool, like this one, to help.

So, your car has a P0300 code, or P0301 code or 302, etc., —your Check Engine light is on, your car is likely running rough, maybe even sputtering, or you’re experiencing bad gas mileage. 

In this video, our mechanic shows you how to diagnose and fix the ignition coil that may have triggered the P0300 code (“Random/Multiple Cylinder Misfire Detected”). Watch now:

Check Engine Light? Misfire Detected – Code P0300 – Ignition Coil Diagnosis

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P0496 code: Mechanic advice to diagnose & fix

P0496 Code
Evap Flow During a Non-Purge Condition

If your Check Engine light is on and your scan tool lets you know your car has a P0496 code, which is an Evaporative Emission Control (EVAP) System code, this means something is causing fuel vapors to escape from your car that shouldn’t. 

In this video, our mechanic shows you how to diagnose the problem that triggered P0496 using common EVAP purge valve tests. Watch now:

Check Engine Light? EVAP Flow During Non-Purge Condition – Code P0496 

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