What is the actual use of the OBD2 Mode 9 Calibration ID (0904) and Calibration Numbers (0906)? Are they constant or do they change? If so, under which circumstances?

I have read the standard, but I'm afraid besides explaining the decoding, it's not very helpful in the actual meaning of these PIDs.

(Background is: I'm developing an iOS ScanTool and wonder whether there is any use in displaying them).


This mode really only serves one general purpose with a few sub-modes:

  • Lock/Assign the ECU to a particular VIN
  • Display the CALID or CALibration IDentification which is basically the "software version" of the ECU, which reflects specific parameters of that particular vehicle. This could be changed by reprogramming or "flashing" the ECU, and might change as a result of an emissions-related recall or other service which changes any part of the engine operation which affects emissions (basically anything). In rough IT equivalency terms it tracks a "Windows Update ID". It will likely also be vastly different on the same physical ECU hardware used in different vehicles and/or engines.
  • Display the CVN or Calibration Verification Numbers, which are internal checksums the ECU uses to prove it has a valid calibration software flashed. The CVNs (there can be several) are intrinsically linked to the CALID and every bit of the ECU flash. A kind of validation "crypto lock" basically, similar to a "Windows COA code", but is generated from a checksum routine. It's worth noting this internal checksum is computed and verified every drive cycle.
  • Display IUPR or In Use Performance Ratio numbers which indicate how real-life driving triggers the OBD monitors compared to a theoretical model of a drive cycle. There are two numbers for each monitor, the first is the numerator and is an accounting of how many times conditions were met for monitoring a particular emissions vector (e.g. HO2S, Evap, misfire, etc.) during valid drive cycles. The second number is the denominator, which counts how many total times the vehicle was driven. The ratio can be resolved as a percentage, which assures ECU programmers that their drive cycle is reasonable.

I believe that all four of these sub modes may be used by Federal and CARB type agencies to certify the vehicle meets current legal standards and can be certified and sold. As an aside, this in part is how Volkswagen got into so much trouble with their "tweaked" diesel ECU flashes. The software recognized the emissions drive cycle dyno test, and shifted into a totally different set of reduced power and performance lower-emissions parameters that would almost never occur in any actual driving condition. Pitbull becomes toy poodle when under testing scrutiny. A Volkswagen "Kobayashi Maru" for you Star Trek fans...

NONE of these items have much service-related scantool value, in my opinion. Tuners are well aware of these numbers, as a misstep can render an ECU inoperable if certain parts of this information are not updated correctly. Usually the flashing software knows how to make any ECU flash tune "valid". New York State emissions inspections use Mode 9 to verify the ECU expected VIN is identical to the registration, and flags if there is a difference - e.g. in some vehicles this means you can't grab a junkyard Mercury Mountaineer ECU and throw it into a Ford Explorer. While the ECU works, the NYS emissions software knows immediately this isn't the proper ECU, and may not have the correct emissions calibration. (Perhaps the Mercury features 10 extra HP as an OEM marketing ploy?)

This is not a rumor or tale; NYS DMV moved to revoke my Inspection License because I unwittingly passed inspection on an Explorer who's owner had done a junkyard ECU swap but did not get the proper calibration reflash. Their suspicion was that I was scanning a different vehicle than the one that was being inspected. I digress...

It's also a cheap (but easily defeated) way to provide a stumbling block to tuners and "hotrodders" tweaking an engine for greater output while sacrificing emissions performance. It could also be used to by a Dealer as reason to dishonor a vehicle warranty if unauthorized changes are detected.

In any event, might be a nice feature to have in a scan tool, especially the VIN and CALID, but the information would be display-purposes FYI at best.

Mode/Service $09 – Request Vehicle Information

The purpose of this diagnostic service is to enable the external test equipment (scantool, tester) to request vehicle specific information such as:

Vehicle Identification Number (VIN) Module Calibration Number (CALID) Calibration Verification Number (CVN) In-use Performance Ratio (IUPR) values The VIN is a unique number which identifies the vehicle. It’s defined by an international standard and every vehicle in use has an unique VIN.

A unique CALID is required for each emission-related calibration of the electronic control unit (ECU). Even if only one value of the ECU calibration data is changed, a new CALID must be generated.

A CVN is linked to each CALID. It’s basically a checksum of the ECU calibration, which is calculated at every driving cycle and stored in the non-volatile memory of the ECU, so that it can be read with the the engine ON or OFF.

IUPR are counters which display how often OBD monitors are triggered in real driving conditions compared to a standard homologation cycle. These are required for the most of the OBD monitored systems (exhaust catalysts, oxygen sensors, exhaust gas recirculation (EGR), secondary air, etc.).

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