OBD 2 diagnostic system

What is the difference between OBD 2 and OBD 1? The communication speed known as the baud rate is much faster on the newer system. Also with OBD 1 each car maker used their own codes and definitions for identifying failures in the computerized engine management system. This made it difficult for auto mechanics servicing multiple vehicle brands. Note: The Equus 3140 is available below. It scans many OBD I and all OBD II cars(Check application chart before purchase).

With OBD2 "generic" or common code definitions where developed to identify all basic emissions related failures regardless of make, model, foreign or domestic. This standardization simplified diagnosis and the tools that interface with the control module. OBD 2 trouble codes consist of one alpha character followed by a four digit description.

The alpha character indicates the area of the vehicle were the failure occurred. This includes B for body, C for chassis, P for power-train, and the letter U for network.

The network would be considered a manufacturer specific code used only on a specific model or brand. The body includes the airbag system codes.

This includes all discriminating crash sensors, clock spring and the air bag deployment module. The chassis would include ABS codes as well as suspension codes if the vehicle is equipped with active suspension. The power train includes the transmission and engine codes.

This is by far the most common system to set computer trouble codes. The first digit of the diagnostic trouble code denotes the origin of the code. Check engine light codes authored by the Society of automotive engineers or, SAE are identified by zero.

Generic OBD 2 codes

These codes are known as generic diagnostic trouble codes since they are the same for every vehicle. A generic P0301 code stands for cylinder misfire detected on cylinder #1 regardless if the failure is on an Asian, German or Domestic car.

If the first number is a one, this could indicate a manufacturer specific code. These diagnostic trouble codes are part of the manufacturers influenced diagnostic software and vary among car makers.

The second digit in the diagnostic trouble code identifies the system where the malfunction is occurring. The number 4 is used for the fuel vapor recovery system and the number 3 is used for the ignition system (as in the example above). The last two digits correspond to specific codes.

OBD 1 and OBD 2 are similar in that both systems check sensor and actuator circuits for opens, shorts, high resistance in ohms and out of range values returned to the ECM.

However, the failure limits for OBD one are far more forgiving, since a circuit or component must fail completely before the check engine light is illuminated or a diagnostic trouble code is stored. Some would call these the good old days.

In contrast obd2 use a series of high speed monitors or diagnostic tests that conduct performance evaluations on mostly emission components. If a monitored circuit fails to meet minimum standards the malfunction indicator lamp is turned on even though the circuit may still be operating.

OBD II sensors and subsystems

The power train control module will illuminate the check engine light to notify the driver and store a diagnostic trouble code to aid in the mechanics diagnosis.

This capability makes it possible for emissions related problems to be identified and corrected before excessive pollutants are discharged in the atmosphere via the tailpipe. This of course only works if the driver heeds the warning light and seeks service. On the big bang theory Penny has been driving around with her service engine soon light on for five seasons.

OBD2 will monitor lots of stuff like misfire detection, fuel control, exhaust gas recirculation (ERG functions), catalyst efficiency, oxygen sensors and all O2 sensor heating circuits, evaporation emissions system (fuel vapor), plus AC refrigerant levels on some models that have climate control. OBDII monitors are said to be continuous or non-continuous. As the name indicates continuous monitors run at all times.

These monitors include EGR (exhaust gas recirculation) components, misfire detection and fuel control. The remaining monitors or noncontinuous, since they do not run until certain criteria has been met.

Enable criteria will include specific driving and engine operating conditions that must occur before the PCM (Power-train control module) will execute or activate the MIL (malfunction indicator light) and store a hard code. PCM's can also store pending codes where multiple failures are required before activating the warning light.

Consequently, if the vehicle is driven in a way that does not satisfy the enable criteria for a particular non-continuous monitor that monitor will not run and no codes will be set even if a real time circuit problem exists.

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After you pull your code the quickest way to a successful repair is to follow a diagnostic chart. Take a look at video demonstration I put together using web based service manuals to fix cars at home.

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