We had a regular customer stop by the house with a check engine light on. I whipped out my Innova 3100i that I keep at home and pulled a code P0131.
This is a pretty common code that stands for oxygen sensor voltage low. Often people want to try replacing the sensor, but this is just one reason the code will set.
I would say only about 50 percent of the time, replacing the part solves the problem. This article covers the quick story of diagnosis and repair of this code and includes some screenshots from the diagnostic tree chart. My customer’s car is a 2008 Nissan Altima with a 3.5 L engine.
The P0131 is a generic code and can set on any car. A quick sidebar, most of these cars are the four-cylinder version with a 2.5 L.
This Gentleman special ordered one with the V-6 that you can find in the older 350 Z. Anyone considering purchasing a Nissan Altima should drive one with the V-6 before they settle for the four-cylinder model. What a difference 2 cylinders makes on this light weight car.
Diagnosing O2 Sensor Problems
When you pull up a diagnostic tree chart for code P0131 in Mitchell 1 or a similar auto repair manual first impression is this code can be pretty complicated to resolve.
If you hang in there and start to go through the steps it’s not as bad as it looks. One thing I was surprised about is Nissan refers to the sensor as an AF sensor.
Although I get it, because this component is actually measuring the air fuel ratio and making adjustments to it I’m just from the old school where we called it an O2.
Another thing to get past was in the manual they talked about using the specialized diagnostic tool that Nissan technicians use at the dealership level. I was able to accomplish the same goals and retrieve the needed information with my extremely simple innova scan tool.
When diagnosing this code it often boils down into two common problems. Either the sensor has failed and isn’t producing voltage or there’s a problem in the wiring harness that supplies power, ground and returns reference signals to the PCM.
The conditions that set the code P0131 are constant low voltages or sensors that are fixed at 0 V. As I have discussed in previous O2 sensor diagnosis articles the voltage that’s monitored by the PCM (Powertrain Control Module) should be constantly fluctuating.
At the high and low points of these changes it should reach a maximum of 900 mV and a minimum of about 100 mV. This exhaust gas sensor should never be fixed at a particular voltage.
And it should never read 0 V. A quick test of the voltage on terminal four of the harness side should read battery voltage. I checked this with a $25 meter that I’ve had around for a decade. There was 0 V at that terminal.
Discovering What Happened to this Car
As we all know, sometimes troubleshooting car problems is like solving a mystery. I had 0 V going to the oxygen sensor and a diagnostic tree chart indicates that the most likely cause is an open in harness.
As I looked at the underside of the vehicle I could see that this car had a story to tell. The car was clean and shiny from the outside but the undercarriage of the vehicle was packed with mud and dirt and there were dents and signs of damage to the floorboards.After showing the customer, he told me that his son borrowed the car the day before. Next morning the check engine light was on. After careful interrogation of the young driver he told the true story.
He took the 2008 Nissan Altima out into the woods to do some four wheeling. He said it kept up with his friend’s bronco and the trails weren’t too harsh.
One of the possible causes of the P0131 code is an open in the harness that runs to the sensor. This is exactly what happened to this 2008 Nissan. Something jumped up from the trail and literally cut the harness.
In closing I have two things to mention. When you’re repairing a harness to an oxygen sensor circuit, you really don’t want to use quick crimp connectors.
This circuit operates on millivolts and some resistance can develop in a crimp connector as time goes on. No. 2 is I would be happy to sell you a new sensor.
On the left is one that fits the Nissan product line. But what I wanted readers to get from this story is when you set an oxygen sensor voltage low code this doesn’t mean the part should be replaced automatically.
In the end a dead sensor can cause this problem but it needs to be diagnosed. Please like and share this page with a friend. Also visit the main check engine light page for more articles about specific codes. Visit the YouFixCars.com homepage to find out what else we cover.