P0140 Diagnostic Trouble Code: An In-depth Analysis

When you start your vehicle in the morning and hit the road for your daily commutes, the last thing you want to see is that ‘little panic-inducing engine warning light. Unfortunately, this warning light pops up on millions of car dashboards on the road every year.

Of course, you’ll want to scan the car and pull out the engine code. If the scan tool pulls out a P0140 error code, you’ll start wondering what P0140 causes are and how to diagnose and fix the leading cause.

Here, we’ll explain the meaning, symptoms, causes, and how to track and resolve the culprit. We have good news for you. A P0140 will not leave you stranded on the road or dig a hole in your pocket.

p0140 vw

What does P0140 mean?

Every internal combustion piston engine has at least two O2 sensors—one before the catalytic converter and the second after the catalytic converter. The O2 sensor measures the number of toxic gases in the exhaust system. Then, it relates this data to the powertrain control module to determine how effective the cat con is running every time.

If the car computer shows the error code P0140, it means that it cannot determine how effective the catalytic converter is running at that moment. This doesn’t necessarily mean the cat con or a lousy oxygen sensor is bad, just that it is not getting any reading from this sensor and component.

For this reason, the car computer is left behind the curtain. And it has to inform you that there’s an underlying issue by illuminating the engine warning light and logging the error code P0140 on VW or your respective car models. So let’s look at the possible P0140 symptoms you should watch out for.

What are the symptoms of error code P0140?

Most of the time, if your vehicle logs a P0140 trouble code, it’ll only project the engine warning light on the driver information center. You won’t have any other noticeable symptoms unless you take a smog check.

You’ll likely fail the emission test whenever your vehicle has a check engine light from an emission-related issue. Since the car computer can’t read the emission information, the emission tester won’t give an accurate reading, causing the vehicle to automatically fail the emission test.

Here’s what you need to know. If the bank 1 downstream oxygen sensor is not sending information to the engine control module, it may raise the Nox emission levels. Of course, this does not affect the vehicle’s performance, but it is not good for the environment.

What could cause a P0140 code?

There are two common causes of a P0140 code on Chevy Silverado and other car models. This includes damaged, burnt, or frayed wiring or faulty oxygen sensor. A faulty catalytic converter and lousy MAF sensor can also cause it, though it’s unlikely.

This wiring issue can occur when road debris or object cuts the wiring or a technician forgets to plug the oxygen socket after working on the car.

  • Defective catalytic converter
  • Faulty wires or connections
  • Lousy MAF sensor.
  • Faulty O2 sensor

How serious is error code P0140?

I understand you don’t want to see that ‘little monster light’ on your dashboard, but a P0140 is a common issue compared to other engine codes. In fact, there’s a chance everything is functioning as it should.

It is very important to fix a P0140 error code to clear the engine warning light so that you can know when the car computer detects a more serious issue and triggers the engine warning light.

Driving with this code will keep you unaware of what’s happening within different car components. And this can lead to premature wear on several system units. However, a P0140 code has no major direct effect on your vehicle performance.

How to diagnose error code P0140

If you love checking and fixing faulty underhood components, you may want to track the root cause of a P0140 on Chevy or your respective car models at home. You’ll need a proper guide to avoid spending unnecessary cash. This simplified P0140 how-to-fix guide will walk you through the entire process.

Tools and items Needed.

  • Multimeter
  • Scan tool

Step 1: Scan the vehicle

As always, run a scan check on the vehicle to ensure there are no other logged trouble codes. If you see other codes, fix them before proceeding.

Step 2: Examine the wires and connectors

Slide underneath the vehicle with a lying board and examine the O2 sensor wires and connectors. Focus more on the bank 1 downstream sensor wiring and connectors and look for burnt, frayed, or lousy wires and connectors.

Step 3: Inspect the exhaust system

While under the vehicle, examine the pre-catalytic converter, exhaust necks, and pipes. Afterward, proceed to the underhood and inspect the exhaust manifold for leaks. If you see any leaks, fix them, erase the pending trouble code, and test-run the vehicle for 20-30 minutes and see if that solves the problem.

Step 4: Test the Oxygen sensor

Slide under the vehicle again with your multimeter. Locate the downstream O2 sensor (the one after the catalytic converter) and test it with the multimeter. Turn on the ignition key and disconnect the oxygen sensor socket. Do not revolve around the car. Test the sensor by following the instruction in your car service manual.

Step 5: Inspect the mass airflow and the engine ground

Test the mass airflow and ensure it is working as supposed. After that, locate the motor ground and check for loose fittings and connections.

Step 6: Seek professional help

If none of the above steps resolves the problem, consult your service technician to track and proffer a solution to the culprit.

Common P0140 diagnosis mistakes

The most prominent mistake amongst DIYers and mechanics is not checking the mass airflow sensor for proper operation. If the mass airflow sensor is faulty and not measuring the air entering the intake, it can cause the P0140 issues. While this is unlikely a probable cause, do not ignore it during diagnostics.

p0140 code

How do I fix code P0140?

After diagnosis and clearing all the fault codes, you’ll likely need to do one or more of the following to fix the P0140 on a VW Golf or any car model.

  • Replace defective oxygen sensor
  • Clean the mass air flow sensor and see if that fixes the issues
  • Replace faulty mass air sensor
  • Replace defective cat con.

Approx. Repair Cost

Several issues can likely cause the P0140 trouble codes. This makes it impossible to estimate accurate repair costs without a proper diagnosis. So, if you want to take the vehicle to a repair shop, budget to pay for an hour of diagnosis. Most shops charge $75 to $150 per hour.

During the diagnosis, they’ll pinpoint the exact cause of the problem and can accurately say the repair cost of the issue. In the case of a P0140 on Hyundai or other car models, the repairs needed to fix the problem and the costs are outlined below. Note that it may require one or more of the following.

  • Replacing a defective cat con $350 to $2,000
  • Replacing a faulty oxygen sensor is $100 to $310
  • Fixing exhaust leaks is $750 to $200 (if welded).

Final Words

Regardless of the leading cause of a check engine light on the driver information center, do not ignore it. Yes, we explained that a P0140 is a common issue but ignoring it may indirectly lead to a catastrophic breakdown.

Hence, it is important to fix any issues that cause the car computer to trigger the engine warning light on the dashboard. We’ve outlined the probable causes, symptoms, severity, and how to diagnose and fix the problem. Follow the guide religiously to track and fix the leading cause of a P0140.

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Osuagwu Solomon

Osuagwu Solomon is a seasoned automotive technician for the past 9 years, and a technical writer. He loves writing about auto professional repair guides, DIY repair guides, and buyer’s guide. After spending six years in the automotive workshop, he decided to impact his knowledge to people aside his domain, and he has achieved this by centering his Automotive writing skills on REPAIRS.

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