Misconceptions and oddities about our platform

IllogicTC

Well-Known Member
There's a bunch of things that keep cropping up around the Internet. Some of it pops up here, but usually is quickly corrected, however there's tons of sites where people quote certain things as fact. I'm trying to compile a list of common assumptions and the truth behind what they're talking about. Any help is appreciated.

"The oil gauge reads a nice 40 at idle but I'm having oil troubles!"
The oil gauge in the I6 does not provide an actual gauge, but a simulated readout. There is only a switch detecting oil pressure, so it's either off (0PSI) or on (reads 40PSI, but can be 12+)

"My key fob has terrible range! Why isn't the antenna on top working?"
The receiver for the key fob is actually located in your liftgate control module, in the back of the vehicle. The antenna (if present) is for OnStar.

"A4WD just turns on 4x4 when I need it, it's 2-wheel drive otherwise."
Partially true. When you turn to A4WD, two things happen. 1 - The front axle locks together. 2 - The transfer case partially engages. There is actually a clutch pack leading to the front in the transfer case, and in A4WD it moves between 5% and 100% torque as necessary.

"My 4x4 isn't working! I turn the switch, the light flashes but nothing happens, the switch must be broken!"
Not likely. If the light is flashing above your selection, that means the TCCM has received the proper position feedback from the switch and is engaging or attempting to engage your selection. If it backs off, there is likely an issue elsewhere in the system.

"That grille in the B pillar next to the driver door must be part of the OnStar system, right? Like a microphone?"
No. That grille actually contains a small fan and a temperature sensor, and is part of the automatic HVAC system, providing feedback to the controller to adjust the blend doors and fan speed. Your OnStar microphone (if equipped) is located in the overhead console, where the grille is up there.

"My A/C compressor has a mind of its own! I don't have the A/C turned on on the console but it is still running, or cycling!"
This is actually normal behavior. In some modes the compressor may turn on and off intermittently. If defrost is active, the A/C will remain running in an attempt to keep the windows from fogging. This is covered in the owner's manual for further reference.

"All my lights are going crazy on my instrument cluster! It must be bad."
Maybe, maybe not. This is also a fairly common symptom of an issue with the class 2 serial data bus. If there is a short in the data bus, or a failing module transmitting "garbage" over the line, it may be misinterpreted by other modules. This can show up as strange behavior in other parts of the vehicle, such as door controls not working, or the instrument cluster going bananas. A Tech II tool can help determine if a module is not communicating properly.

"My cruise control won't come on, or comes on and turns back off! Must be broken."
Maybe. Do you have a Check Engine light by chance? There are certain failure conditions which will disable cruise control. Cruise control is done digitally on this platform, rather than mechanical methods like the old days.

"My wheel hub makes a noise during a left turn, that means my passenger side is failing, right?"
Maybe. Convention would say yes, because that's where there's more "weight" thanks to physics during the turn. But there's been reports of it actually being the opposite, where this scenario would mean the driver's side is out. Best practice would be to replace both as a matching pair, it's a great opportunity to inspect your front brakes while you're at it.

"I accidentally locked my keys in my car again! Why didn't they do anything about this?"
They did. If the key is completely in the ignition switch, the driver door will lock, then unlock. If not, if you have OnStar you can call them for assistance. There is one more option - delayed locking. To activate, hold the driver door lock/unlock toggle in the lock position, then hit unlock twice on your key fob. This will cycle between delayed locking and "regular" locking. Test it out once - when you hit lock, it'll chime three times. Five seconds after all doors are closed, the doors lock. You can reverse this by following the same steps.

"I start my car on a cold night. The lights are dim for like ten seconds and the voltmeter reads only 11.5! Then all of a sudden everything brightens up and the gauge shoots up to 15. Is something broken?"
This is likely normal behavior. There is a system in place in the modern alternator that can actually disable it for a moment while the engine gets going and stabilizes. It then activates the alternator and that's when everything brightens up.
 

kdannyk

Well-Known Member
Very interseting, I read through your write up. It's very knowledgeable. I didn't know about the cold starting with alternator or what the back drive panel thing was.
 

freddyboy61

Well-Known Member
Very nice write-up. I have comments on two items;

When the 4WD select switch lights continue to blink and don't go to steady on, that usually means that the TCCM did not get the correct feedback from the actuators and the commanded task was not fully completed.

As far as the alternator controlling its output voltage, that is something that the PCM actually takes are of. Don't know specifically what conditions this happens under, but cold temperatures is definitely one of them.
 

Robbabob

Well-Known Member
Great write up. If you are looking to make a list of common misconceptions, or put differently, a list of "Oh, that's how that works, you can do that?"

Who would think the passenger side door module can operate the drivers window if moved to that wiring harness?
 
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IllogicTC

IllogicTC

Well-Known Member
freddyboy61 said:
Very nice write-up. I have comments on two items;

When the 4WD select switch lights continue to blink and don't go to steady on, that usually means that the TCCM did not get the correct feedback from the actuators and the commanded task was not fully completed.

As far as the alternator controlling its output voltage, that is something that the PCM actually takes are of. Don't know specifically what conditions this happens under, but cold temperatures is definitely one of them.
I will update the main post with this information!

Oh wait, I can't :sadcry:
 
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IllogicTC

IllogicTC

Well-Known Member
"I got pulled over for doing 60 in a 55. I was only doing 53, that's exactly what the speedometer said!"
Are you absolutely certain? The stepper motors which control this and the other gauges are a very common failure point in the vehicle. When you pulled over, did the gauge go below the 0 mark? Or does it sometimes hang in a particular position, reading like 5 mph when you're stopped? The easiest way to verify the accuracy of your speedometer, if it's questionable, is to use a GPS for independent verification, or an OBD-II scanner with live readout showing you the current vehicle speed if you trust that it's likely the gauge and not the vehicle speed sensor.

"My fuel gauge is always sitting at empty and the dummy light's on, the gauge must be broken."
The dummy light is controlled independently of the gauge, meaning you could have the gauge three marks below E and the light wouldn't turn on unless the fuel sending unit is reporting empty/near empty. While your gauge may also be toast (see above), the light coming on also when you know you've got way more than a couple gallons left in the tank is a pretty obvious indicator that your fuel sending unit (in the fuel tank) is junk. It was an especially common issue during a couple years of production, 2004 and 2005, and GM offered essentially half-price repair/replace for it.

"My dimmer knob doesn't affect the brightness of my door controls/is delayed compared to everything else. Why?"
There's actually 3 parts affecting dimness in the interior lights, all controlled by that one knob. It's all located in the BCM. There's one part that controls the incandescent (old-fashioned) bulbs in the dash. Another affects only the LEDs (like the radio display). The last one, and this is important, isn't a variation done by the BCM at all, but a message sent through the Class 2 serial bus to the door modules telling them what to turn the brightness to! This is why sometimes the door control dimming happens a bit slower, or may seem to be "broken" in relation to all the other lights. They saved running one wire to each door and in turn increased the complexity of the door modules (and thus the price :hissyfit:).

"My window was frozen recently and I got it to go down only a bit, but it worked fine otherwise. Now if I click the Auto, it only goes down to where it stopped the other day!"
The Auto function on the GMT windows is interesting. Rather than have a limit switch to physically detect when the window has reached the bottom of travel, the module monitors the draw on the motor. Ever notice that when it's working right, the window will go all the way down then sound like power is still to it for maybe 1/8th to 1/4 of a second? When an electric motor is prevented from moving, its current draw increases and the module uses this to "know" when the window is at the bottom. If your window was frozen where it'd only go down just a bit, the module then relearned how long to run the window before turning it off in Auto. The solution is to keep hitting Auto down after it stops, until it actually reaches the bottom. Then roll it back up, then hit Auto again and see if it goes all the way back down okay. If not, keep repeating, this will usually help the module relearn about how long to run the window motor.

More to come!
 

djthumper

Administrator
Although it is in the technical discussions of the platform maybe the thread title should read misconceptions of the platform or something to better reflect what the thread is. I almost looked past the thread because of the title. :confused:
 
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IllogicTC

IllogicTC

Well-Known Member
the roadie said:
If only you had mod powers. :wink: What was your user name back on trailvoy? :undecided:
Probably the same as it is on here, back when I was a noob with all questions and zero answers :rotfl:

I figured a compendium of common questions may be a fun read for people who are new to the platform so they can understand what isn't always explained at the dealer or manual, and have a handy link to point people to regarding their questions :thumbsup:

Any chance you could cut my second post with more Q&A and append it to the original post? :biggrin:
 

Einst-Hawk

Well-Known Member
Love this Thread!!

Thanks IllogicTC
 

Envoy_04

Well-Known Member
Following the Q&A format, here's a couple you could add to the list of oddities.


"Every time I start up my engine in the morning or after work I hear a loud whining sound that goes away after 30-40 seconds, do I have some sort of vacuum leak or a worse problem?"
No, the shop-vac like noise you're hearing is coming from below the body directly under your butt, and it's the Secondary Air Injection System (SAIS) pump running. This pump runs on cold start only to supply oxygen to the exhaust gases to help them catalyze quicker until the catalytic converter warms up. Common problems with this system involve the pump getting water in it and becoming extremely loud or ceasing to work, and the solenoid for the system that is mounted on the exhaust manifold sticking open or closed thus preventing the air from blowing into the exhaust or allowing exhaust to blow back through the lines. The diagnostic code related to this system is P0410.


"My vehicle checked out fine in the front end when I checked the ball joints and tie rod ends for play, and it drives fine, but every time I hit a bump in the road I hear a pronounced thump or rattle from the front end, what on Earth could be wrong?"
It is highly likely that your anti-sway bar end links have gone bad, as this is a very common problem. When you buy new ones, beware that even the most expensive greasable Moog ones you can get will fail in a year or two just like the OEM or the cheap ones will, the ball and socket design is too weak for the application, some consider it a design flaw. Suspension Maxx makes end links that are upgraded and are said to last longer, plus they're rebuildable!


"I've noticed that the rear door rubber seals are sagging in the fenderwell area, which means they're worn out and need replaced. Man do I hate to spend all that money just to get the rubber to stay up, it still looks good and feels nice and soft!"
Chances are that they're not worn out, most GMT360s had sagging rear door rubber a year or two after they were new. A cheap and easy fix is to make sure the track in the rubber is clean, and then use some glue or silicone in the track and put it back up where it belongs. Shut the door to hold it in place and let it dry.


"There's a red wire under the hood near my battery, something must have a short and the PO unhooked it to keep the battery from draining. Can anyone tell me what it supplies power to and why someone would unhook it?"
The small red wire by the battery was actually left unhooked from the factory! It will power the pin on the wiring plug at the rear with 30 amps that will charge a battery on a trailer when it is connected to the lug nearest the motor (The one by itself, not either of the lugs with the large megafuse connected) on the front of the fuse box. If you tow a trailer with an onboard battery, hook it up for battery charging! If you don't tow, it's best to leave it alone.
 
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IllogicTC

IllogicTC

Well-Known Member
"I went to change my spark plugs; when I removed the coil pack for cylinder 4/5, I looked in before starting and noticed there was a little bit of water in the bottom/a little rust on the bottom of the plug! Is something broken, did I blow a gasket or something?"
This is actually a known problem. Notice that there's no weatherstripping (rubber seal) on the back of the engine compartment, either on the hood or the body metal. What happens is sometimes in the rain or when running your wipers, some water trickles down onto the block and may get past the coil pack "seal." I use the term loosely because there's only one bolt toward an extremity holding the pack down, so it's much more difficult to get a proper seal around the entire perimeter. If there's some water present, soak out what you can, and let the rest evaporate until dry before removing the plug. When reinstalling your coil packs, you could ensure the area where the seal touches, and the seal itself, are completely clean. Making sure the bolt is properly torqued can aid in sealing. The gasket that is by the inside of the spark plug wells is actually used to retain oil; if you find oil in the spark plug well, THEN you have a bad gasket.

"I have a light that came on, I looked it up and it's the Reduced Engine Power light. How does it know I'm not getting full power, and what did I break?"
Luckily, this isn't just any issue causing the REP light. The REP light comes on when the expected position of the throttle plate and the actual position of the plate do not agree. Imagine this: you're accelerating briskly, and then you let off the gas pedal when you reach the speed you want. Suddenly the REP light comes on. Did you blow something? Is a valve stuck from your little bit of fun or something that is making you lose power? Luckily, it's not (relatively speaking) that severe! What likely happened is that you let off the accelerator, which tells the PCM to close the throttle, and then the throttle didn't go to where it was supposed to. This system is designed to give you a "limp" mode to at least be able to safely pull over or get to a shop/home if you're not far away, and it compromises by not allowing the throttle to open very far. This ensures that you are much less likely to have a runaway vehicle like we all remember Toyota doing a massive recall for. And yes, your GMT360 is drive-by-wire.
 

Envoy_04

Well-Known Member
"Some of the lights in my factory radio have been burnt out for a while, and now more buttons seem to be burning out. All the buttons and functions work fine, but the buttons just don't illuminate any more. I'm not an aftermarket head unit type person, am I doomed to pay for a costly "rebuild" from a specialty shop or to try and get my VIN programmed into a radio that is comparable to mine that I find at a junkyard or on ebay?"
Don't get rid of that factory radio just yet, there's hope for it still! With just a few dollars in some 3mm and 4mm 14V bulbs, and a little patience and time with a soldering gun, you can have that radio lit up like the day it was new! This task isn't hard, but it is moderately difficult - if you're not comfortable taking the face off of the radio and soldering in the new bulbs then find a friend who knows how to solder, or practice first on something else that isn't important. For under $20 you can get your radio, and using the same steps your HVAC controls, to be illuminated as you remember them.
 
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IllogicTC

IllogicTC

Well-Known Member
"Why is there a little red light on on my mirror?"
Your OnStar (VCIM) module has experienced some sort of malfunction. It could be a loss of cell reception, or a problem interfacing with the radio, or a bad backup battery... quite a few things, actually.
"But I don't have OnStar service!"
That doesn't stop the OnStar module from checking on itself and making sure it's okay. You may not have the OnStar service, but the module's diagnostics are complementary, I guess.
 
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IllogicTC

IllogicTC

Well-Known Member
"I shifted into 4HI and heard a big bang from the front! What did I break? The manual says I can do this at any speed!"

Let me quote it from the 2005 TrailBlazer manual, page 2-28:

Shifting Into 4HI (Four-Wheel High) or A4WD (Automatic Four-Wheel Drive)
Turn the knob to 4HI or A4WD. This can be done at any speed unless you are shifting out of 4LO. The indicator light will flash while shifting. It will remain on when the shift is complete.

It does say exactly that, right there, it can be done at any speed. Well, here's an oddity about the platform... IT LIED! It may work this way if the vehicle is new off the lot, but as things wear the operating characteristics change, one of them being the transition speeds of the encoder motor and the front axle disconnect actuator. Our system is interesting in that the driver's wheel is NEVER disengaged from the front differential, and the passenger side is just disconnected via the front axle disconnect. Now, when you're driving down the road in 2HI, your driver wheel is spinning forward of course, which in turn means that the intermediate shaft leading to the disconnect turns backwards!

Now, we have an intermediate shaft on one side of the disconnect spinning backwards, and the other side of the disconnect (being turned by the passenger wheel) is turning forward, so they're turning in opposite directions. When the vehicle is new, everything may work out where the encoder motor will actuate briskly and get the intermediate shaft spinning before the actuator engages the two shafts, but if not, you're trying to connect two things running in opposite direction to each other, and this may cause some sort of damage.

The general recommendation is to switch to 4HI only while taking a slow-moderate pace, perhaps 20MPH tops, to minimize the potential for overstressing (and breaking!) front axle disconnect components.
 

Envoy_04

Well-Known Member
"Every vehicle is a little different, where should my temperature gauge run at under normal conditions?"
Straight up! The temperature guage should stay steady at 210 degrees F or at most one tick to the left. Any cooler and the engine will be running too rich, and any hotter and it will be too lean. Thermostat replacement is the way to fix the situation, as it can stick open, closed, or partially between. If the needle on the temperature gauge varies a lot, such as moving during hard acceleration, then the coolant temperature sensor needs replaced.
 
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IllogicTC

IllogicTC

Well-Known Member
Envoy_04 said:
"Every vehicle is a little different, where should my temperature gauge run at under normal conditions?"
Straight up! The temperature guage should stay steady at 210 degrees F or at most one tick to the left. Any cooler and the engine will be running too rich, and any hotter and it will be too lean. Thermostat replacement is the way to fix the situation, as it can stick open, closed, or partially between. If the needle on the temperature gauge varies a lot, such as moving during hard acceleration, then the coolant temperature sensor needs replaced.
It's also noted that just because the gauge says 210 doesn't mean it's running 210. The numbers are just there to look pretty, it's all about the position of the gauge as described here. If you plug in a scan tool, you'll notice the gauge reads a solid 210, but your scan tool (as in actual, calibrated data) will read 195-200. 195 is the thermostat target temperature.
 

Chickenhawk

Well-Known Member
If your parking brake lever suddenly meets little resistance when you pull it up and you just had your car washed at a full service car wash, look up the procedure for tightening the cables at the lever before you spend time and money looking at the parking brakes themselves. Aggressive vacuuming near the area of the parking lever boot can cause the adjuster latch to slip out of place.

I make it a practice to test and use my parking brake once a month.
 

Mark20

Well-Known Member
Envoy_04 said:
"Every vehicle is a little different, where should my temperature gauge run at under normal conditions?"
Straight up! The temperature guage should stay steady at 210 degrees F or at most one tick to the left. Any cooler and the engine will be running too rich, and any hotter and it will be too lean. Thermostat replacement is the way to fix the situation, as it can stick open, closed, or partially between. If the needle on the temperature gauge varies a lot, such as moving during hard acceleration, then the coolant temperature sensor needs replaced.
If you're replacing the thermostat you should replace the coolant temperature sensor right next to it.
 
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IllogicTC

IllogicTC

Well-Known Member
"I went to do my transmission fluid and filter, and I was asked whether I had the deep or the shallow pan. I told them my engine and everything, they still asked! What does this mean?"
Some of the 4L60E transmissions equipped indeed had a shallow pan, while others had a deep. I'm not entirely sure if there were certain years, serial ranges, or options which would distinguish which pan you got or if it was just a supply/manufacturing thing. But luckily it's easy to check!

The deep pan is about 2 3/4" deep, and has a noticeable "step-down" maybe 1/6-1/4 of the way back on the pan. From what I gather, the shallow pan is maybe 2" deep, and apparently is flush the whole way across the bottom surface. There may be a spot stamped in the corner or something, but there is NO step-down, the pan is the same depth the entire way across.
 

AtlWrk

Well-Known Member
Mark20 said:
If you're replacing the thermostat you should replace the coolant temperature sensor right next to it.
...except for some years (e.g. 2006) where the sensor may be located on the top rear passenger side of the block. Of course it still stands that you should replace it since you will already have the coolant drained.
 

Envoy_04

Well-Known Member
This one's for Envoy owners - I'm sure it applies to the others as well. It may seem a bit obvious, but in my experience folks either don't know or just don't think of it until they crawl under and look or read about it.

"My Envoy's fog lights point down on the road so close in front of the vehicle that they're almost useless, I've almost quit using them altogether because they just aren't effective."
Your fog lights ARE adjustable, just like your headlights. Near the wires where the bulb plugs in at the back of the fog light assembly behind the bumper, there is a small adjustment screw that sticks down. It takes a torx socket to turn it, I believe the same size as the easily accessible headlight one up top. Loosening this screw (counter-clockwise) will raise the light upward and make it shine further down the road. Tightening this screw (clockwise) will lower the light and make it shine closer to the ground directly in front of your bumper. Use small adjustment increments, a little bit of a turn equals a lot of light beam movement.
 
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IllogicTC

IllogicTC

Well-Known Member
Envoy_04 said:
This one's for Envoy owners - I'm sure it applies to the others as well. It may seem a bit obvious, but in my experience folks either don't know or just don't think of it until they crawl under and look or read about it.

"My Envoy's fog lights point down on the road so close in front of the vehicle that they're almost useless, I've almost quit using them altogether because they just aren't effective."
Your fog lights ARE adjustable, just like your headlights. Near the wires where the bulb plugs in at the back of the fog light assembly behind the bumper, there is a small adjustment screw that sticks down. It takes a torx socket to turn it, I believe the same size as the easily accessible headlight one up top. Loosening this screw (counter-clockwise) will raise the light upward and make it shine further down the road. Tightening this screw (clockwise) will lower the light and make it shine closer to the ground directly in front of your bumper. Use small adjustment increments, a little bit of a turn equals a lot of light beam movement.
Mine were already pointed a bit up. Works great for making signs stand out at night and make them more easily-read.
 

fishcreek

Active Member
If it is -40C out, chances are you have the ABS and Service Brake System on.
 

dmanns67

Well-Known Member
Envoy_04 said:
This one's for Envoy owners - I'm sure it applies to the others as well. It may seem a bit obvious, but in my experience folks either don't know or just don't think of it until they crawl under and look or read about it.

"My Envoy's fog lights point down on the road so close in front of the vehicle that they're almost useless, I've almost quit using them altogether because they just aren't effective."
Your fog lights ARE adjustable, just like your headlights. Near the wires where the bulb plugs in at the back of the fog light assembly behind the bumper, there is a small adjustment screw that sticks down. It takes a torx socket to turn it, I believe the same size as the easily accessible headlight one up top. Loosening this screw (counter-clockwise) will raise the light upward and make it shine further down the road. Tightening this screw (clockwise) will lower the light and make it shine closer to the ground directly in front of your bumper. Use small adjustment increments, a little bit of a turn equals a lot of light beam movement.
This is true for TrailBlazers with OE fog lights. We have an adjustable screw that runs through a spring on the back side of the fog light, but you need to take the fog light completely out of the bumper cover to make the adjustment. Only three bolts hold the fog light in, very quick adjustment.
 

mcsteven

Well-Known Member
Misconceptions only by is or by others?

Others (the salesman who sold it to me):
This truck has almost 300 horsepower from its V-6 motor.

Mods: feel free to delete if out of context with the rest of the thread
 
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IllogicTC

IllogicTC

Well-Known Member
mcsteven said:
Misconceptions only by is or by others?

Others (the salesman who sold it to me):
This truck has almost 300 horsepower from its V-6 motor.

Mods: feel free to delete if out of context with the rest of the thread
I consider it in-context. So many 6-cyl are made in V form now that it's just said, sometimes out of ignorance and sometimes just out of habit. But it is important to know if you want to really understand the vehicle.

The dealer rambled on to me about the air ride in the rear. I don't have air ride.
 

HARDTRAILZ

Moderator
I love that people ask at least once a month "What is that?"

Almost makes me want to badge it.
 

mcsteven

Well-Known Member
I don't know if it is the same for all years, makes and models, but the light on the door jamb is not burned out. It's a reflector, not a lamp (unless you've gotten the mod bug).
 
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IllogicTC

IllogicTC

Well-Known Member
mcsteven said:
I don't know if it is the same for all years, makes and models, but the light on the door jamb is not burned out. It's a reflector, not a lamp (unless you've gotten the mod bug).
As far as I know, it's a reflector for all years. I can actually only recall one vehicle (I believe it was my mom's Taurus when I was a kid) having lit door jambs. I even had a couple vehicle that didn't have any reflectors or lights (both older trucks).
 

BowTide

New Member
IllogicTC said:
"I went to do my transmission fluid and filter, and I was asked whether I had the deep or the shallow pan. I told them my engine and everything, they still asked! What does this mean?"
Some of the 4L60E transmissions equipped indeed had a shallow pan, while others had a deep. I'm not entirely sure if there were certain years, serial ranges, or options which would distinguish which pan you got or if it was just a supply/manufacturing thing. But luckily it's easy to check!

The deep pan is about 2 3/4" deep, and has a noticeable "step-down" maybe 1/6-1/4 of the way back on the pan. From what I gather, the shallow pan is maybe 2" deep, and apparently is flush the whole way across the bottom surface. There may be a spot stamped in the corner or something, but there is NO step-down, the pan is the same depth the entire way across.
Would that be part of the factory tow package??

IllogicTC said:
"I shifted into 4HI and heard a big bang from the front! What did I break? The manual says I can do this at any speed!"

Let me quote it from the 2005 TrailBlazer manual, page 2-28:

Shifting Into 4HI (Four-Wheel High) or A4WD (Automatic Four-Wheel Drive)
Turn the knob to 4HI or A4WD. This can be done at any speed unless you are shifting out of 4LO. The indicator light will flash while shifting. It will remain on when the shift is complete.

It does say exactly that, right there, it can be done at any speed. Well, here's an oddity about the platform... IT LIED! It may work this way if the vehicle is new off the lot, but as things wear the operating characteristics change, one of them being the transition speeds of the encoder motor and the front axle disconnect actuator. Our system is interesting in that the driver's wheel is NEVER disengaged from the front differential, and the passenger side is just disconnected via the front axle disconnect. Now, when you're driving down the road in 2HI, your driver wheel is spinning forward of course, which in turn means that the intermediate shaft leading to the disconnect turns backwards!

Now, we have an intermediate shaft on one side of the disconnect spinning backwards, and the other side of the disconnect (being turned by the passenger wheel) is turning forward, so they're turning in opposite directions. When the vehicle is new, everything may work out where the encoder motor will actuate briskly and get the intermediate shaft spinning before the actuator engages the two shafts, but if not, you're trying to connect two things running in opposite direction to each other, and this may cause some sort of damage.

The general recommendation is to switch to 4HI only while taking a slow-moderate pace, perhaps 20MPH tops, to minimize the potential for overstressing (and breaking!) front axle disconnect components.
Glad to know that info!! My old 95 Tahoe with 200k you could pull that lever into 4hi at any speed and it engaged smoothly (don't want to lose momentum in the sand)
 
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IllogicTC

IllogicTC

Well-Known Member
BowTide said:
Would that be part of the factory tow package??

Glad to know that info!! My old 95 Tahoe with 200k you could pull that lever into 4hi at any speed and it engaged smoothly (don't want to lose momentum in the sand)
I don't think it is. It seems more based on which supplier had shipped in the next set of pans, as they both hold the same quantity as far as I can remember (5 quarts).
 

Einst-Hawk

Well-Known Member
I'm not sure if this is an oddity on just our platform or an oddity for GM in general.

When I was changing my rear differential fluid, I changed the gasket as well. GM part number - 12479020

The gasket itself seems to be a perfect octagon with the bolt holes evenly spaced. It is not.
I found out that this gasket will go on 'perfect' one way and one way only.

It might look like you have it on right, but if the bolts start getting harder to go in the more you go, then it is not right. I mean it is only a millimeter off and you can make the bolts go in, but it will feel almost like they are cross-threading or going in at an angle.

It does seam straight-forward to match a gasket and cover together. Just dry fit the gasket on the cover. Flip, turn, flip and turn until the holes match. I found that there are quite a few different positions that this gasket can be in and look 'right'. And the only way to know if you got if right is to try to bolt it up.

I had to match up the gasket and cover several different ways before I found the correct postion. You may think I am crazy, but this was my experience.

Not sure if this applies to aftermarket gaskets since I used AC Delco from a dealer.
 

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