Ok, obscure questions coming up: some folks on here are familiar with OBD noncontinuous monitors (OBD-NCM). OBD-NCM are sensor data recording certain events as they randomly occur during the drive cycle.

(Answers in below posts) I suspect that if (for example) the OBD-NCM "value" for the catalytic converter, or O2 sensor, or whatever, reach a certain threshold, it'll trigger a code. Can anyone confirm that it works this way?

Question 1. What does "Passed" Mean? Why is the "value" Min/Max between 0 and 65000 in all cases? Why is (apparently) anything in this range listed as "Passed"?
OR: does "Passed" simply mean that the noncontinuous monitor works, and is NOT a comment on the "value" or "0-65K range" at all -- it would say "passed" whatever the values are, as long as the sensor works?

Question 2: Is there a source for the correct "value" ranges? Most of the "value" reading in the each of the MIDs are 0. Some, like this cylinder 5 misfire count of 15, are something else than 0. Some, like an O2 sensor MID, are in the range of 2500. I understand the (obvious) misfire count, but have no reference for other "values" that are non-zero. Anyone know where there data that measures normal and non-normal values for the OBD-NCMs? Is a O2 sensor "Value" of 2500 good, bad or meaningless?

Question 3: The easy one. In the top pic below is a capture of my Cylinder 5 misfire noncontinuous monitor (MID $A6 and $A7) from my OBD scanner. The misfires identify Cylinder 5 -- the only one with misfires. The second pic is a cylinder map for the 4.2 engine Is this correct that cylinder 5 is as it is labeled in this pic?

Yeah, I'm a car geek, but the NCMs have some pretty interesting data...if I can figure out what the data means......

Thanks!

 

The min 0 and max 65535 reading just tells me that your device is reading with a 16 bit resolution.
OBD data should be post-calculated with a formula dedicated to the type of reading in order for the data to make sense.

See the formula column in the table on this site:
https://en.wikipedia.org/wiki/OBD-II...w_current_data
Some formulas contains this same 65535 number. ((2^16)-1)

 

Thanks, Bob. Great info reference.

So, the "range" is just up to 16 bits wide of data memory.
The value within the range is generally determined by a formula, some of which are listed in the Wiki reference you offered.
At some point, level unknown, a value may change enough to trigger a code. The actual trigger is sometimes standard within the OBD spec, or sometimes manufacturer specific.
For example, the fact that there's, say, 15 misfires in the MID is something to note, but we have no idea what the misfire formula is to trigger a code. (The only example I foundan answer to is that LT fuel trim triggers a code at +/-20%, when the "correct value" is 0% and typical is +/- 5% or so.)
"Passed" means that it met some formula-driven setpoint in the range, meaning both that the sensor works, and that the data captured is acceptable.

Thanks -- that answers it.

Panthera

 

I think you're using a meaning of NCM I've not met before. I wouldn't get too attached to it.

I'm pretty sure it does not work that way.

The various values/thresholds are in Jaguar documents, some variants of which we have on here or are on the net. Try words such as

JAGUAR ON-BOARD DIAGNOSTICS V8 ENGINE MANAGEMENT SYSTEM

very possibly with

DENSO

they're usually PDF files.

Some are in the large file area IIRC.

 

Thanks, outstanding document from May 2004, but it does cover the 4.2L engine I use. I've attached it below for those who don't have it.

The document does support my process description above, though my language isn't as precise as it could be as I learn more. I'm referring to the Wikipedia article provided by Cabrio Bob, an excellent introduction to the subject, plus the much more detailed triggering and calculation information in the doc attached below.

ODB Continuous Monitor: A condition monitored continuously by one or multiple sensors >>> analyzed through program routines in the ECU >>>generates a DTC if out of designed range. LT Fuel trim is an an example. The designed range that triggers a code is listed in the doc below.

ODB Non-continuous monitor: A single test of a specific set of sensor conditions >>>analyzed by the ECU program >>> result recorded in the format specified in the Wikipedia article, in memory as specified by SAE.J1979 (or more current engineering spec) The single test and result may be repeated once or more in a drive cycle. A result outside criteria set by the designers will trigger a DTC. So, my use of "randomly" is not precise, since the test iterate from very specific triggering conditions. An example is the catalyst efficiency measurement starting on pg 14. Again, designed range is often listed in the doc below.

Also, this is correct, since the NCM test sequences reach an error condition and trigger a DTC : "I suspect that if (for example) the OBD-NCM "value" for the catalytic converter, or O2 sensor, or whatever, reach a certain threshold, it'll trigger a code. Can anyone confirm that it works this way?" Yes, it works that way, albeit in more complex patterns, according to the document below.

The doc below also answered my curiosity about how many misfires it takes to trigger a code. For my engine, at 1000 rpm, it takes around 150 misfires in 200 engine revolutions to trigger a catalyst damage misfire code.So my minimal 15 misfires in cylinder 5 is pretty damn trivial -- though it might indicate the very beginnings of a weakening coil.

Again, many thanks for the doc. It's a great addition to my library and answered a lot of questions about how the monitors worked.

Best, panthera.

 

I'm glad you found that. BTW there's a newer & bigger version (4/2008, 152 pages) but I think it's too big for this site's limits. It's essentially the same of course.

I think it has more of the "mode 6" stuff but unless you're really keen it's not exactly exciting.