OTC Monitor 2000 & the GM Herd

Padgett (C) 2005-2009


Fig. 1 OTC Monitor 2000 was available with a broad array of options


For my computer cars, I find the OTC Monitor 2000 to be both ideal and inexpensive. While lacking some of the features of a Tech-1 or Snap-On scan tool and replaced by the OTC 4000, for someone fascinated by odd-ball GM two seaters of the 1980s (Fiero, Allante, Reatta) or the Buick powered Vixen motor home the 2000 provides everything needed and less.

GM has produced computer cars in three basic flavors, the original Computer Command Control (CCC) of approximately 1981-1988, the P4 used from 1988 to 1995, and those OBD-II compliant from 1995-on. All were based on the Motorolla 680X architecture (some say GM's massive consumption of 6800s in 1981-83 delayed availability of the 68000 used by the Macintosh and allowed the PC to become dominant but that is another hobby). There was some overlap as new engines received the new architectures first while older lines continued until replaced. For this reason, all Fieros are CCC while all Reattas are P4. To the scan tool this is not important since both are handled implicitly.

Since 1981, GM has used a serial data link called the Assembly Line Data Link or ALDL to move engine information from the computer to scan tools in the form of a string of data bytes. The sequence of these bytes and their contents are different for each engine series. For this reason the scan tool must know the model year and the engine code (VIN 8) to be able to interpret the data stream. This also means that the scan tools cartridge must include the carline, model year, and understand the engine code (though there is some overlap - a 1989 GM cartridge may be used for a 1990 Bonneville).

The data stream includes a wealth of data about how the engine is "feeling" including recode of all trouble codes, RPM, battery voltage, coolant temperature, whether fans are on or off, whether the Transmission Controlled Clutch (TCC or "lockup") is active, the transitions of the O2 sensor, MAF or MAP flow rate, injector pulse width, mixture correction factors, and many more - everything needed to accurately diagnose problems often before they are noticeable.

For over a decade I have had one or more OTC Monitor 2000s. The first was given to me by a friend who was a Snap-On dealer and had taken it in trade and used it for several years for our Bonneville and assorted Fieros. It has proven very useful for the herd here since my newest is a 1992 Pontiac TranSport.

Since all of my cars are GM I just tape the GM ALDL adapter to the unit but optional pieces are available for Ford, Chrysler, and a number of Imports as well.

The best part is that 2000's regularly appear on eBay for prices ranging from $10 to $30 for a serviceable unit with GM cartridge, adapter, and cards. For slightly more you might find a complete set with books, adapters, and case. The rarest item is a cable that can connect the OTC 2000 to an RS-232 serial port on a PC for snapshots and sequence capture.

But all that is really needed are the three items mentioned and the monitor itself.

The Pieces

  1. The Monitor
    The OTC Monitor 2000 is a handheld device somewhat larger than a PDA with a front panel consisting of a digital (LED) display, a selection of specific indicators surrounding the OTC logo, a keypad, connectors for ALDL adapters and power (12vDC), and a slot in the bottom to insert a configuration cartridge.

    Fig. 2 OTC Monitor 2000 Device
  2. The Adapter

    There are many adapter cables for the OTC Monitor 2000 to allow connection to the many different carlines but in this case we need only be concerned with one: the GM two row adapter. This is a cable with a round connector on one end to attach to the Monitor and a two row twelve pin connector for the GM ALDL socket.

    Fig. 3 - the GM ALDL adapter cable

  3. The Cartridge

    The information pertaining to how to interpret the data stream from the ALDL is contained in a cartridge. You will only need one but it must cover the model year of your vehicle(s). A 1988 GM cartridge will cover any year Fiero or the Vixen.

    Fig. 4 Various Cartridges that may be used with GM Vehicles

    Year is important element. May be "GM", "3-in-1", or "Pathfinder", later will include "Domestic".

    Fig 5 - GM, Ford, Chrysler, and Import Cartridges

  4. The Cards
    There is really only two cards needed depending on the vehicle. Of the interesting cars, only the 4-cyl Fiero used a TBI (throttle body injection), other used either SFI (sequential fuel injection) or TPI (tuned port injection). These fit into a holder in the back of the device. Many more cards exist for other car lines.

    Fig. 6: Sample GM Cards (note - later years have more information and are divided into TBI, Carb, and PFI After 1990 there was also a transmission card for the THM "E" transmissions.

    In practice, the unit is very intuitive, often the hardest part is finding the ALDL connector in the vehicle (on a Fiero is is behind the plate on the console that covers the cigarette lighter, on a Vixen, it is in the front fuse box).

    With the ignition off, plug in the ALDL connector, then the power plug into the cigarette lighter (if an APU is used, the ground must be connected to the vehicle chassis).

    The 2000 display will display stars and the panel with flash then the logo and a request for vehicle information. Once all data is input select "standard display" and it will probably show "no data". Turn the ignition on and all values will start to display but will be of a stopped engine (rpm=0000). Starting the engine will display run time information selected. For example mode 1 will show rpm and battery voltage. Mode 3 will display any stored trouble codes and the PROM ID (most displays will have two different data points - see card or book for other modes and displays).

    ps The Pathfinder modules have the most complex setup but can also remember the last set of parameters. When the setup is done, there will be a series of statements and comments, often just pressing "1" repetitively will skip to the next. Also since many modes have more than one digit, after entering to mode number it is necessary to push "Enter" to finalize.

    Weasel words: The methods described above worked for me on my cars but may not work for everyone.  I do not speak for GM and they do not speak for me. Your mileage may vary. Notary sojack y'all.

    contents copyright Padgett 2002-2009 except as noted.

    OTC Monitor 2000 is copyright OTC Corp

    Pontiac, Fiero, Reatta are copyright GMC

    Vixen, Vixen SE are copyright Vixen Motor Corp.