Pin 13 is the pin use use to ground to check codes.
If you did indeed ground #13 the 4wd light will blink
Code "1" is "RAM standby power" and is considered normal, may be caused by clearing the codes.
Code "2" is "Encoder fault"
Code "3" is "TCCM motor circuit"
Code "4" is "RAM/ROM failure"
Ground pin 13 at the data connector under the dash. The lights on the switch should flash. You are only going to have a choice of 4 codes as mentioned above. Here is the procedure to further clarify.
Diagnostic Trouble Code (DTC) Displaying:
The transfer case shift control module is equipped with the ability to store diagnostic information, which is useful to a technician in the event of module, component or wiring failures. This information can be retrieved from the transfer case shift control module by way of flash codes, which are displayed on the three transfer case shift control switch buttons. These buttons are located on the instrument panel to the right of the steering wheel Before obtaining DTCs, perform the following transfer case control module (TCCM) Self-Test.
Observe the transfer case shift control switch indicators while turning the ignition switch to RUN. A properly operating system will flash all indicators and then will return to the current gear. If the system is operating normally, then proceed to Displaying Codes.
If the TCCM failed the Self-Test, then test the following circuits.
Battery Positive Voltage, and Ignition Voltage for battery voltage
Ground Circuit for ground
Diagnostic enable circuit for an open or high resistance
Transfer case shift control switch connector
If the above circuits are normal but the TCCM still fails the Self-Test, replace the TCCM.
Turn OFF the ignition for 10 seconds.
Connect PIN 13 on the data link cable (DLC) to a ground. The DLC is located in the cab under the instrument panel on the driver's side.
Turn ON the ignition, with the engine OFF.
Observe the transfer case shift control switch select buttons for flashing codes. Refer to Diagnostic Trouble Code (DTC) List above.
Important: If the transfer case shift control switch buttons all blink only once and then stop, no fault codes are stored in the transfer case shift control module.
When one DTC is stored in memory, that code will blink that number of times followed by a 3 second pause and then repeat.
If more than one code is stored, the first code will blink, followed by a 3 second pause and then the second code will blink.
This sequence will continue until PIN 13 on the DLC is no longer grounded.
If the TCCM will not communicate the presence or absence of DTCs, test the above circuits in Self-Test Step 2. If the circuits are complete, then replace the TCCM.
Here is a break down of your 4WD system::D
1) let's start off with the easy things -- have you checked your fuses? Don't assume that just because the fuses are labeled 4WD that they are the only ones for your 4WD system! Fuse 10 (on the Jimmy/Blazer) is for the courtesy lights but guess what? It also controls the logic side of the TCCM (+5VDC). Pin 6 (thinner orange wire) should produce +5VDC and should be HOT AT ALL TIMES (meaning you should be able to read +5VDC on the line anytime, key on or off). The two large orange wires are your +12VDC lines and are controlled from the 10A fuse located in spot #15.
Check your LARGE orange wires as you are getting +5VDC logic as the lights are coming on on the dash. The +12VDC is used for the encoder motor, check to make sure you have +12VDC at both the large orange wires (they are right beside each other, and there are two large black wires beside them that are ground).
Notes: All black wires are ground -- all orange wires are power (hot). There is a 10A fuse (#15) for the 4WD system, located in the fuse panel. There is a 20A fuse, located under the hood, that is also for the 4WD system (I'll have to look up the fuse number). The 4WD system also pulls from the 10A courtesy lamp fuse (#10).
2) The vacuum switch (located on the firewall http://www.kylestubbins.com/files/bl...uum_switch.jpg
) or vacuum diaphram (located under the battery) could be malfunctioning. The job of these components is to pull on a cable which engages the front, right 4WD hub. I don't think this is likely to be your problem as you should probably hear the encoder motor running (changing the drive mode from 2Hi to 4Hi/4Lo) but there is a sensor on the hub to tell the TCCM when it is engaged, so it could be problem.
3) the encoder motor/module is bad. This is the module/motor that is mounted directly to the transfer case, who's job it is to physically move the gears of the transfer case to put the TC into the various modes (2Hi, 4Hi, 4Lo). You also want to check the wires at the encoder motor as they are exposed to the elements and could be damaged by something flying up under your vehicle (not likely, but possible).
4) The TCCM (located under the passengers kick panel) has wires that are corroded / broken. Poor connections anywhere along the route will cause problems and most times intermittently, which are a real PITA to find. The TCCM could be bad as well. If I had to guess either your encoder motor is shot, or bad wires on the TCCM.
If you're really into it, I'll post the schematics for the wiring of the system -- this will allow you to trace and test points along the system to pinpoint the problem. I hope I have given you some direction to be able to start troubleshooting your 4WD system. ;)
Here is a picture of your wire harness to your TCCM that you need to inspect for corrosion and damaged wires. http://kylestubbins.com/files/images...r_tccm_01d.jpg