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99 Blazer,4.3 (VIN W), 4WD, auto trans, four button electronic transfer case (I believe it’s the autotrac option. I can say for sure the right option code is NP8 and it’s a NP236 transfer case. ), with code C0387 – transfer case failed to shift. I’m going to throw you some back story before I get to the symptoms. It might be a necessary evil.
I put a newer transmission out of a 2000 Blazer into it last week along with a brand new shift cable. After the initial replacement, I can’t remember if I tried hitting the buttons to engage 4HI or 4LO. I do recall that I failed to connect the vehicle speed sensor connector and had no speedometer or shifting capability on the first test drive. Once I found that connector, the transmission has performed flawlessly since. During the trans replacement, I dropped a cap on the front u-joint and lost the needle bearings. Auto Stoned sent me a u-joint that was missing two of the rubber seals for its caps. Time and other circumstances forced me to install the u-joint anyway. Today, I decide that I’m going replace that u-joint at home in the driveway. I tried engaging the 4WD to lock the front driveshaft when I get a nasty clang out of the transfer case.
With the vehicle back on the ground, running, and attempting to shift the transfer case, it will allegedly shift from 2HI to 4HI just fine. By saying allegedly, I mean that the indicator lights by the buttons will say that I’ve successfully shifted from 2HI to 4HI. If I were to shift from two to four, the light on four will blink a few times and then turn solid amber. I never hear or feel anything to suggest that the axle or the transfer case is physically engaged in 4HI. I tried engaging 4HI on the dry pavement once and driving forward. I’m no expert in 4WD anything, but I thought I should have felt some binding from the driveline on dry pavement. (I was otherwise on the lawn for most other 4WD engagements.)
In trying to shift into 4LO, I consistently get a clank/clang when it tries to engage, and then another clank once it tries to retract to the previous range once the shift fails. The clank is consistent whether trying to shift from 2HI or 4HI, The 4LO button will always blink until the module gives up and returns to the previous selected range. The transfer case did shift into 4LO once only and that was while at a crawl on the pavement. The C0387 is my only code.
About the only other things I can think to tell you is that I didn’t use a paper gasket to rejoin the transfer case to the trans, and I replaced the transfer case fluid with the blue GM fluid that belongs in it. I did test the transfer case when I got the Blazer last September with all the wheels elevated off the ground on a drive on lift. I also tried out the 4HI during the winter as needed. I think it worked then because it was a lot harder to throw the Blazer into an oversteer condition around the corners.
So this is where I’m stuck. Thanks in advance for your help.
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