OBD2 for Dummies....

We see several references to code reader being "as good" as scanners for less money..... so let's take a look at what OBD2 codes really are.....
The ones that most are familiar with are "memory codes"... These are the only ones that a code reader can retrieve. Continuous Memory codes (CMDTCs) are a concern that the PCM has seen in the past but may not be present at the time codes are scanned.... This can be a real problem since many codes are present as a symptom of the concern and not as a cause of the concern.
Spending the extra money to step up to a scan tool allows us to perform OnDemand testing. OnDemand codes are concerns that actually exist at the time of the test. The KOEO OnDemand test has us command the PCM to conduct a self test routine and report any problems that exist at the time of the test.... some caution is required - if the engine is cold, the PCM will report back that the engine is cold (not at operating temp). If no OnDemand codes are retrieved, we move on to the KOER OnDemand test - there are several outputs and inputs that the PCM cannot accurately test unless the engine is running.
At the same time, we need to consider any codes retrieved carefully before we act on them... Some codes can be just a response (a symptom) to a concern.... P0171 and P0174 are good examples of these.... These codes are lean exhaust indicators and can have many, many causes other than the O2 sensors. Other codes can be causal codes.... A P1124 can indicate an open or short in the throttle position sensor or circuit.
This should be a decent start for some discussion....
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On Sun, 14 Jan 2007 21:49:59 GMT, "Jim Warman"

I picked up an "auto xray" scanner - it reads set codes as well as current codes, and reads the data from all the sensors. On OBD2 it does not have quite as much detail access as some of the OBD1 systems (my 1994 Pontiac gives me more info than my '96 Mystique). There is a CAN upgrade available, but it will not "exercise" or control anything.
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that's strange. I have an auto-x-ray scanner, and it only reads basic obd1 info. but it will do all kinds of obd2 stuff, including runtime monitoring of the engine. <clare at snyder.on.ca> wrote in message wrote:

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I have an OTC OBDI scanner. It can read data streams and allows you to display four at one time. Had a "no spark" problem on my Dodge pickup. The OTC has a test where it sends a spark every two seconds. After I determined the coil was good I checked the signal from the distributor. The OTC said no spark signal. Took no time at all to find a broken wire in the distributor. My OBDII reader is just that. Worthless.
Al
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Back in the 80s, Dodge had about the best OBD1 system going with "Actuator Test Mode"... With this, we could cycle several of the PCM outputs.... This would tell us if the PCM was capable of controlling things like the ignition coil, fuel injector and some others (been too long to remember).
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wrote:

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clare at snyder.on.ca wrote:

Most (if not all) OBD2 systems are really two systems in one box. One side is the OBD2 that you're seeing on your scan tool, it's pretty basic. Even then, many tool manufacturers leave off certain $ mode capabilities. On the other side is the OEM enhanced, it contains a lot more information than the OBD2 side. The PID list on any domestic enhanced system is very extensive, and like OBD1 entirely at the discretion of the OEM to utilize. The ability to access the enhanced side is largely dependent on how advanced the tool is and [usually] directly proportional the price paid. One can spend enormous amounts of money with the major equipment players and -still- not have full access to all the $modes, PIDS and/or bi-directional controls the OEM has embedded. From what I've seen, Auto X-Ray sells a variety of OBD2 capable scan tools over a range of prices which no doubt means differing levels of capability.
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