CODE PO401 : Insufficient EGR Flow

The Exhaust Gas Re circulation (EGR) system is designed to reintroduce exhaust gas into the combustion chambers, thereby lowering combustion temperatures and reducing the formation of Oxides of Nitrogen (NOx). The amount of exhaust gas that is reintroduced into the combustion cycle is determined by several factors, such as: engine speed, engine vacuum, exhaust system back pressure, coolant temperature, throttle position. All EGR valves are vacuum operated. The EGR vacuum diagram for your particular vehicle is displayed on the Vehicle Emission Control Information (VECI) label. The EGR system is Differential Pressure Feedback EGR (DPFE) system, controlled by the Powertrain Control Module (PCM) and composed of the following components: DPFE sensor (also referred to as the back pressure transducer), EGR Vacuum Regulator (EVR) solenoid, EGR valve, and assorted hoses. The P0401 code means that OBD detected an insufficient amount of EGR. Symptoms There may be drive-ability issues such as pinging ( pre-ignition knock , similar to cheap gas) when the vehicles engine is under heavy load or the vehicle is climbing a steep grade. There may also be other symptoms. Causes A code P0401 most likely means one or more of the following has happened: The DPF (differential pressure) sensor is faulty and needs to be replaced There is a blockage in the EGR (most likely carbon buildup) The EGR valve is faulty The EGR valve may not be opening due to a lack of vacuum Possible Solutions In fixing this code, it is quite common for people to just replace the EGR valve only to have the OBD code return. The EGR valve is not always the cause. If you replace all 3 components the like is all but guaranteed to go away . Or you can test each component . Use a vacuum pump and pull the EGR valve open while monitoring engine RPM's. There should be a noticeable difference in RPM's with the EGR open Clean out the EGR valve to remove deposits Replace the DPF sensor Replace the EGR valve

Diagnosing Your Brakes

Brake problems vary greatly with the make and model of a car, the age of the car and other variables. If your car is experiencing brake problems, bring it to a mechanic. You may, however, be able to narrow down some of the possible problems yourself. Below are some general guidelines. Followed by some helpful troubleshooting hints.

1. Step off the brakes, with the car's engine turned off. A soft or mushy brake pedal indicates that you may be low on brake fluid, or may need to bleed your brakes.
2. If it is safe, drive the car at low speed, braking as needed. You may need new brake pads, or to clean the brakes, if they squeal.
3. In a clear area, step sharply on the brake pedal. If the brakes do not stop the car effectively, several things may be wrong, including worn pads, contaminated brake fluid or contaminated brake pads.
4. If the brakes pull the car to one side, you may need to adjust the brake's clearance, may have to replace the pads or rotors, or may have insufficient hydraulic pressure in one part of the brake system.
5. Begin driving forward slowly. If the brakes bind or drag, it may be due to grease on the pads or scored rotors. Visit a mechanic if you do not know how to fix brakes. Describe the car's performance to the mechanic in as much detail as you can. Check brake fluid regularly. If you have determined that your brakes are bad, avoid driving the car until they are fixed. Computerized brakes, which are standard in many cars, need to be fixed by a mechanic.

MAINTENANCE

Benefits of Proper Maintenance The automobile is a truly amazing machine. It is expected to function under a wide range of weather conditions and other adverse conditions, yet it often is subjected to careless hard driving and indifferent maintenance. Recommended service intervals are often ignored by the same vehicle owners that wouldn't let a week go by without vacuuming all the rugs in the house. Today the automobile is an integral part of our life. We have come to rely on the proper functioning of the family vehicle and seldom, if ever, make a time allowance in case the vehicle should fail to start. We expect it to start and move every time, and fortunately, most of the time it does. However, the rare instance that it doesn't, causes the owner to forget the thousands of times it started without a problem. The irony is that, chances are, the vehicle failed to start because of neglect. A periodic maintenance program such as the one in this book can keep the vehicle owner more aware of the condition of his or her vehicle and will save money in three important areas-fuel economy, emissions and performance.

Oxygen Sensors

OXYGEN (O2) SENSORS

General Information An Oxygen (O2) sensor is an input device used by the engine control computer to monitor the amount of oxygen in the exhaust gas stream. This information is used by the computer, along with other inputs, to fine-tune the air/fuel mixture so that the engine can run with the greatest efficiency in all conditions. The O2sensor sends this information to the computer in the form of a 100–900 millivolt (mV) reference signal, which is actually created by the O2sensor itself through chemical interactions between the sensor tip material (zirconium dioxide in almost all cases), the oxygen levels in the exhaust gas stream, and ambient atmosphere gas. At operating temperatures, approximately 1100°F (600°C), the element becomes a semiconductor. Essentially, through the differing levels of oxygen in the exhaust gas stream and in the surrounding atmosphere, the sensor creates a voltage signal which is directly and consistently related to the concentration of oxygen in the exhaust stream. Typically, a higher than normal amount of oxygen in the exhaust stream indicates that not all of the available oxygen was used in the combustion process, because there was not enough fuel (lean condition) present. Inversely, a lower than normal concentration of oxygen in the exhaust stream indicates that a large amount was used in the combustion process, because a larger than necessary amount of fuel was present (rich condition). Thus, the engine control computer can correct the amount of fuel introduced into the combustion chambers.

Since the control computer uses the O2sensor output voltage as an indication of the oxygen concentration, and the oxygen concentration directly affects O2sensor output, the signal voltage from the sensor to the computer fluctuates constantly. This fluctuation is caused by the nature of the interaction between the computer and the O2sensor, which follows a general pattern: detect, compare, compensate, detect, compare, compensate, etc. This means that when the computer detects a lean signal from the O2sensor, it compares the reading with known parameters stored within its memory. It calculates that there is too much oxygen present in the exhaust gases, so it compensates by adding more fuel to the air/fuel mixture. This, in turn, causes the O2sensor to send a rich signal to the computer, which then compares this new signal, and adjusts the air/fuel mixture again. This pattern constantly repeats itself: detect rich, compare, compensate lean, detect lean, compare, compensate rich, etc. Since the O2sensor fluctuates between rich and lean, and because the lean limit for sensor output is 100 mV and the rich limit is 900 mV, the proper voltage signal from a normally functioning O2sensor consistently fluctuates between 100–300 and 700–900 mV.

NOTE: The sensor voltage may never quite reach 100 or 900 mV, but it should fluctuate from at least below 300 mV to above 700 mV, and the mid-point of the fluctuations should be centered around 500 mV.

To improve O2sensor efficiency, newer O2sensors were designed with a built-in heating element, and were called Heated Oxygen (HO2) sensors. This heating element was incorporated into the sensor so that the sensor would reach optimal operating temperature quicker, meaning that the O2sensor output signal could be used by the engine control computer sooner. Because the sensor reaches optimal temperature quicker, modern vehicles enjoy improved driveability and fuel economy even before the engine reaches normal operating temperature.

On-Board Diagnostics second generation (OBD-II), an updated system based on the former OBD-I, calls for additional O2sensors to be used after the catalytic converter, so that catalytic converter efficiency can be measured by the vehicle's engine control computer. The O2sensors mounted in the exhaust system after the catalytic converters are not used to affect air/fuel mixture; they are used solely to monitor catalytic converter efficiency.