I have a 2002 Trailblazer and the only drive mode working is a4wd. When I put it in 2hi it will sometimes work for a bit but kick out when I stop at a stop light or similar. When I switch it to 4hi the light on the switch act normal but the front axle does not engage, drives like I only have 2wd. When I switch to 4lo the light just blinks and I have only 2 wheel drive. In a4wd it seems to function perfect. Took to my mechanic who is a whiz at diagnosis issues and they ended up replacing the switch in the dash and it worked fine for a week and then went right back to the same issue. Took it back and after spending a day with it they told me that I needed to take it to a transmission shop as the transfer case "may" have issues. Any ideas?
2002 Trailblazer only a4wd working properly
- Thread starter oper8or
- Start date
Roadie I am sure will answer shortly, but generally if your A4WD is working and the 4HI is not, the encoder motor needs to be replaced (a sensor in there is not working which can be cleaned, but I think it is quite a bit of work). Remember, 4LO only works if you are stopped (or moving less than 2 mph, which is pretty difficult to do).
Plus, you have to be in neutral to make the 4LO switch.linneje said:
My first impression is the encoder motor, also, Generally deactivating A4WD will disconnect the front axle halves, and remove the torque from the front side of the transfer case. But I may be wrong - usually an encoder motor identified as being in the wrong position by the TCCM would throw a Service lamp, but I may be wrong on that.
2002 TCCMs are highly suspect, but usually present with different symptoms.
On offroadtb.com we have had a rash of encoder motor issues related to a bad brake solenoid. A4WD mode operates as expected, but 4HI doesn't STAY engaged because the brake isn't holding it engaged. You can bench test for this if you know the theory of operation of the encoder motor, or just swap it.
On offroadtb.com we have had a rash of encoder motor issues related to a bad brake solenoid. A4WD mode operates as expected, but 4HI doesn't STAY engaged because the brake isn't holding it engaged. You can bench test for this if you know the theory of operation of the encoder motor, or just swap it.
the brake solenoid is in the encoder motor along with your faulty sensor , just replace the unit but do not buy a doorman product
No I dont believe so, what you have described is classic encoder motor sensor issues.
Also Encoder motor = Transfer case motor
Also Encoder motor = Transfer case motor
Wiring flakiness is always suspect.
Is it misbehaving now? Can you describe EXACTLY what you see on the switch and hear from underneath the truck (you can do this with the ignition on and the engine off) in each mode transition:
2HI->A4WD
A4WD->4HI
4HI->4LO
4LO->4HI
4HI->A4WD
A4WD->2HI
Is it misbehaving now? Can you describe EXACTLY what you see on the switch and hear from underneath the truck (you can do this with the ignition on and the engine off) in each mode transition:
2HI->A4WD
A4WD->4HI
4HI->4LO
4LO->4HI
4HI->A4WD
A4WD->2HI
As I posted prior you need to replace that motor, and this is why,
- The TCCM monitors the case motor AND the 4wd disconnect
- The TCCM than makes decisions based on its inputs
- As your video verified the switch and the case motor are working and the TCCM appears to be working because it stops the case motor from running
- It is the sensor in the case motor that is faulty
- What is happening is that the TCCM is seeing a change in the case sensor that it is happy with based on a variance such as a half or three quarters of a volt, but than when it stops and reads the actual voltage it does not agree with its software so it does not know if to engage the 4wd disconnect or not and does not know what lights to display on the switch
- Also because of this it may not always fully engage the case itself and could case premature t-case failure
- Hence you need a new Encoder Motor
AND DO NOT BUY A DORMAN
- The TCCM monitors the case motor AND the 4wd disconnect
- The TCCM than makes decisions based on its inputs
- As your video verified the switch and the case motor are working and the TCCM appears to be working because it stops the case motor from running
- It is the sensor in the case motor that is faulty
- What is happening is that the TCCM is seeing a change in the case sensor that it is happy with based on a variance such as a half or three quarters of a volt, but than when it stops and reads the actual voltage it does not agree with its software so it does not know if to engage the 4wd disconnect or not and does not know what lights to display on the switch
- Also because of this it may not always fully engage the case itself and could case premature t-case failure
- Hence you need a new Encoder Motor
AND DO NOT BUY A DORMAN
I'd say it is probably something in the encoder, too. That 2HI-Auto switch time was horrible. Sat there buzzing for what, 10 seconds? Not sure if it only has one speed, or it varies speed as appropriate, but it sounds either like it was struggling against something or that it was hunting to get the proper position for a while.
I'm not the expert though. But that video ought to help the real experts out.
I'm not the expert though. But that video ought to help the real experts out.
Oh lol I should add my experience,
- Automotive diagnostic technician
- Specializing in wiring and transmission rebuilds
- four years with chev
- Three years with dodge junk
- Ten years self employed
- Automotive diagnostic technician
- Specializing in wiring and transmission rebuilds
- four years with chev
- Three years with dodge junk
- Ten years self employed
I cringed through all of that. 
The encoder motor has only one speed. Your front axle actuator is making exactly the right short and high-pitched whine.
The encoder motor is either hosed, or prevented from moving quickly by a gummed up or damaged transfer case.
I don't believe I failed to ask this in my first post, but how many miles do you have, and what's the maintenance history of the transfer case fluid? Has it been changed religiously every 50K as required?
The encoder motor has only one speed. Your front axle actuator is making exactly the right short and high-pitched whine.
The encoder motor is either hosed, or prevented from moving quickly by a gummed up or damaged transfer case.
I don't believe I failed to ask this in my first post, but how many miles do you have, and what's the maintenance history of the transfer case fluid? Has it been changed religiously every 50K as required?
If you watched the video you would hear that the front diff only engaged in AWD , which is typical of a encoder sensor.
Hes also does not complain of any noises and or clunking.
Im willing to wager that its the motor
Hes also does not complain of any noises and or clunking.
Im willing to wager that its the motor
Funny thing, after helping me make the video so that I could show what sound the motor was making, my wife left the switch in 2wd. I did not notice for 2 days and the truck never kicked out of gear. Tried 4hi and 4lo and now all is fine. Must have been just gummed up or something, or possibly a weak motor, but with all the switching back and forth everything is working as it should. Changed the transfer case fluid today. Thanks for all the positive input. At least now I know what to look for if it happens again.
Wow. Didn't see this coming. Thanks for the report.
I'll repeat here what I said for years back on trailvoy - exercise your 4WD system at least once a quarter through all the modes at least ten times. It cleans your switch and makes sure the rest of the parts are there to save your life if you ever depend on the system to work.
I'll repeat here what I said for years back on trailvoy - exercise your 4WD system at least once a quarter through all the modes at least ten times. It cleans your switch and makes sure the rest of the parts are there to save your life if you ever depend on the system to work.
On an even funnier side note, I drove it in 4hi today just to make sure it was functioning and I was pulling into a parking spot at the market I felt the tires grabbing telling me that it was. before I came to a stop I flipped the switch to 2wd and shut it off and went in the store. When I came out my trailblazer had rolled ahead about 40 feet coming to a stop about 6 inches from the side of a Cadillac. Apparently I didn't allow enough time for in to engage before I shut it off and it was in a neutral state. Lesson learned, (almost the hard way).
This is concerning. Switching from 4HI to 2HI DOES NOT disengage the rear wheels at any point. The only time all wheels are fully disengaged is when it's switching from and to 4LO - because there's a planetary gearset in there and it needs to disengage the high gears and engage the low. This "halfway point" between the two speeds is what I also believe is where the Neutral position is, if chosen (it's a secret setting by holding the switch all the way to the right).oper8or said:
The transmission and the rear tires are always connected between all states but the aforementioned. What happens when switching between 2HI and 4HI is a clutch gets pushed together on the side running the front driveshaft. That's it. Everything in there is always spinning except the other half of that clutch when you're in 2HI. It sounds to me like your encoder motor is not properly reporting position (moved too far when going from 4HI to 2HI) or your transfer case is junk.
Also, it is generally not a good idea to use 4-wheel drive on dry pavement. It can screw up that clutch I mentioned, or if the clutch decides to hold tight can severely damage other components, sometimes leading to a dangerous or expensive "wind-up" condition.