Emissions Archives - Page 24 of 24 - UnderhoodService
Diagnostics Through CAN Networks

Since model year 2003, a growing number of domestic and import vehicles have been built with a new onboard communications protocol called CAN (Controller Area Network). CAN is essentially an engineering standard for how computers and modules talk to one another via the serial data bus in a vehicle’s wiring system. It’s a high speed

Better Breathing: EGR Improvements

So Why Do We Have EGR? By Glen Beanard, technical contributor The Exhaust Gas Recirculation (EGR) system was created in the early 1970s for the same No. 1 ranking motivation that drives every other engine management system design — to reduce emissions. The EGR valve targets one specific pollutant, oxides of nitrogen (NOx). Under normal

Tech Update: A to VSV…Troubleshooting Toyota/Lelxus EVAP Systems

When I first had to diagnose a Toyota EVAP code, I found the available information a little lacking. So I decided to do a little homework…and the following article is the result of what I’ve learned. I hope it helps you diagnose and repair these systems a little easier. First, a word on basic EVAP

VW OBD II Revisited: Good Vehicle Service History Helps Determine Causes of Repeat Failures

After 10-plus years of dealing with OBD II, it should be apparent that we are on a learning curve that probably has no end. Almost daily we have a VAG model come into the shop with a check engine light on, or a “state OBD II failure” form. Although we have the latest scanner software

Exhaust & Emissions: Converters & O2 Sensors

What’s the most important emissions control device on a vehicle today? The catalytic converter, because it cleans up any exhaust pollutants that exit the engine. It’s a hot job (literally) with operating temperatures running between 600 to 1,000

Exhaust Parts

Too Much Weight

Diagnostic Solutions: Air Flow Sensors…Understanding Their Function & Potential Problems

Most of us remember the “good old days” when an engine’s air/fuel (a/f) ratio was controlled by a mechanically operated carburetor. Due to the inherent design limitations of mechanical systems, however, carburetors don’t respond efficiently to changes in barometric pressure, temperature and humidity. In the quest for improved fuel economy and reduced exhaust emissions, import

Replacing Oxygen Sensor: Saving the Environment and Your Customer’s Catalytic Converter

The oxygen (O2) sensor is the master switch in the fuel control feedback loop. The sensor monitors the amount of unburned oxygen in the exhaust and produces a voltage signal that varies from about 0.1 volts (lean) to 0.9 volts (rich). The computer uses the O2 sensor’s signal to constantly fine tune and flip-flop the

OBD II Diagnostics: Checking into Mode $06

In this scan tool diagnostics article, we take a look at Mode $06 functions which govern non-continuous monitors (EVAP, catalyst, EGR, etc.)

Monitoring Emission Efficiency With O2 Sensors

As modern OBD II technology marches on, it’s clear that the zirconia-based oxygen sensor now is being sold more as a basic repair part than as a preventive maintenance part, and it changes the way we diagnose and sell oxygen sensors. To illustrate the difference, let’s remember that an oxygen sensor replacement used to be

Checking into Mode $06

Mode 06 is the actual system test data that OBD II looks at when it decides to set a pending code or a current fault code. If the test data is within the limits established by the vehicle manufacturer, the item gets a PASS and no codes are set. But if a value is out of range, OBD II flags it with a FAIL and keeps an eye on the component until the system monitor has run at least twice. Then, if the problem is still there, a DTC is set and the MIL light comes on.