2004 Trailblazer LT 4.2L L6

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Oxygen Sensor and Catalytic Converter

O2 Sensor Details

Front - ACDELCO 2131698 {#12586996} GM Original Equipment - Alternate/OEM Part Number(s): 12586996

Rear - ACDelco 213-1574 GM Original Equipment Heated Oxygen Sensor

Testing O2 Sensor Wiring

Did you check fuse #29 (O2 SNSR)? That supplies power to the heating elements of both oxygen sensors and would throw the P0053 if blown. I would then check for 12V (with the ignition in RUN) on the pink wire (terminal D) at the O2 sensor connector.[1]

Sensor Locations

Secondary Air Injection

  • for now:
  1. wait for your car to be "cold" or 4 hours. Disconnect the hose from check valve (located passenger side--the transmission dip stick is attached to the bolts that hold it to the block). Start the truck, you should hear a nasty sound for about 30 seconds to a minute. If you don't its your check valve.
  2. If it is your check valve, you can try to clean it. Get some throttle body cleaner, remove the check valve spray thouroughly (I did it a couple of times to get all the carbon and rust out) and let dry reinstall and follow above instructions. If no go replace check valve
  1. wait for your car to be "cold" or 4 hours. remove the fattest hose from the underside of air intake hose (I think thats where it is, I have a CAI so Its hard to know where it is exactly OEM) and from the check valve. Have someone else start the truck. Feel the hoses, you should feel sucking and blowing (I can't remember which is supposed to blow / suck) If you don't feel anything then its the pump (maybe -- read further)
  2. check fuses there are about 3 in the manual listed for air pump (if bad fuse replace and retest, make sure to check the fuses after to make sure that the pump isnt blowing fuses)
  3. Locate the air pump its driver side mid car just behind the cross member for the frame. There are two wiring harnesess one that goes into the relay (grey box) and one that has two fat wires (thats the power plug for the pump.) disconnect that one, wait for cold start and start truck while having a multimeter attached set on DC mode. If you get a reading of 0 then replace the relay. if you get power 12-15 volts replace the motor.
  4. If both the check valve and the pump are testing out ok it could be a clogged hose.

Exhaust Manifold


Trailblazer Manifold Notes

Unscrew, Screw In, Unscrew More

If you buy new bolts from GM, they come with pre-applied high temp threadlock compound.

The torque process is three passes, done in that sequence from inside to outside, each pass done to 18 lb-ft. Exhaust pipe nuts are 37 lb-ft.

Then try turning the bolts out 1/8th turn and then back, then 1/4 turn and back 1/4. This should loosen the locktite. Then do 1/4 and back 1/8th until you feel the bolt is loosening, then up it to 1/2 turn and back 1/8. until it is out. It is time consuming but this worked form me..

CRC Freeze-Off Super Penetrant can work too.

Anyway, the actual replacement procedure isn't too taxing. One tip that I'd like to point out is that during the installation portion of the job, apply a 0.2 inch (5mm) bead of threadlock (GM P/N 12345493), or equivalent to the threads of the exhaust manifold bolts. Do NOT apply sealer to the first 3 threads of the bolts. The walk-through that we followed was very adamant about that![2]

12345493 = Permatex High Temperature Threadlocker RED[3]


Possible explanation for conflicting advice on using threadlocker on header bolts:

When installing headers, the instructions suggest, recommend, or insist that you re-torque the header bolts after 100 miles or so. GM can't do that on factory engines, so they use the high-temperature threadlocker to keep the bolts from backing out.

GM's advice, in the shop manual for R&Ring the exhaust manifolds, is to use the threadlocker since no customer is going to come back in 100 miles to have his or her exhaust manifold bolts retorqued.

So what should I, the semi-skilled amateur, do when I install my Kooks - be a GM tech, or leave the threadlocker off and check the bolt torque until it stabilizes, if ever?[4]


Camshaft Position Actuator Solenoid Cleaning

Putting an AMP in

Throttle Body

Blower Motor Resistor

Recalibrate Vent Actuators

  • Disconnect the Battery for a while
  • Make sure all vent stuff is off
  • Turn car on, let sit for 60 seconds at least


39 HVAC 1

Start car, leave on for one min.

Clean Sending Unit

Use alot of this at once: Chevron 65740 Techron Concentrate

Replace Dash Stepper Motors

This is where I got mine:

They work great

Replace Thermostat and Temp Sensor

I do not think I should have done the temp sensor...what a pita. Some people say go through the wheel well. I did not and it seems like it would have been easier through the wheel well. But then some people say it is harder. You will have to find those instructions.

Doing by taking the alternator off:

Fuel Filter

Brakes Soft, Pedal Travel

Sounds funny but, I had new brake fluid put in, did some other stuff. I had to engage the ABS on a dirt/sand road and the pedal firmed right up.

  • Some Issue: I wouldnt ever push the brake fluid back thru the master cylinder. It will mess up the ABS. I dont know the exact reason but every vehicle that I've seen with that done the ABS will throw a code and act funny. Best thing to do it crack the bleeder when re-seating the pistons back. Other than that, I dont have a fix for ya.


After a LOT of researching, I decided that the ABS system needed to be cycled. Not necessarily bled, as there should be no air in the system, but at least cycled in order to undo whatever I did to it when I back-pressed the caliper pistons.

After more digging, I discovered I had two choices: I could take it to a dealer and have them "bleed" the ABS according to the shop manual's process using their Scan Tool. Our local dealers want a hundred bucks just to hook the Scan Tool up!

Other choice was to force the ABS to cycle itself, and hope that would reset it. It was worth a try, and if it didn't work there was still the dealer.

Following the instructions I found, I took the truck out to a loose-gravel road (just a quarter mile from home, out here in the countryside). Starting cautiously, I got up to a blistering 10 mph and stomped the brake pedal hard as I could. With all my strength, I was able to get just a half-dozen barks out of the ABS. But that was enough. The second time, the brakes applied a little harder and the ABS barked a little more. Each time, I could go a little faster and hit the brakes a little harder.

A couple dozen repeats of this, speed up to 50 mph near the end, was probably over-kill. But that fixed it!

I gave it one more bleed to be sure, and there was no air in the system. So after I made the mistake of pressing the fluid backwards through the system, I just needed to "reset" the ABS by forcing it to cycle itself. (I don't think the new master cylinder was a bad idea, either.)

So thanks, Donut Slayer! Your comment got me on the right track. And I'll never back-push the fluid in an ABS system again. Open the bleeder and press it out into a container.

End Quote

Basically same as above:

Remote Key / FOB Relearn

Installing GPS and feeding it with On-Star Wire

Cannot remember exactly which wire but I spliced into the onstar mirror control. There where two wires feeding 12 power to it and its associated circuitry.

Steering Wheel Loose Rubber Fix

This stuff works great! I used it, be careful with the needle. It is called SLT99 Steering Wheel Bonder. It will leave bumps so do it well.

I purchased the SLT99 Steering Wheel Bonder Kit. It comes from Australia so it takes a bit. The aussies always have cools stuff. Same country that I got the rack boots from. Universal power steering rack boots. Made it easy.

Password Entry

They do not have a FOB with a password on it. You have to install a unit in the car, and the wireless fob integrates with that.


I did a lot of stuff trying to fix my transmission. I replaced solenoids, and a accumulator piston. NEVER TOUCH A TRANNY UNLESS YOU WANT TO REBUILD IT. I ended up purchasing a new transmission from rockauto. Best thing ever. EM REMAN / TRANSMISSION AUTHORITY rebuilt tranny with all the little fixes they are supposed to have over the years. The thing works great and has a 100,000 mile warranty.

I mean, replace a Solenoid...if a code says its bad...but I would never do anything else. I swapped fluid at the same time as the solenoids and Accumulator Piston. It worked for about 1000 miles and something fucked up.

You read and read and read...people talked about replacing pistons like they are nothing. What they do not tell you is that the piston cover has a paper gasket that is huge and part of the tranny really. When you take it off, you rip and mess the gasket up. What a mess. Never again.

O well. The Tranny was having shift problems when I got it and the dealer lied to me about how many miles were on the Tranny.

Fuel Regulator

Car running like garbage? At least notice something?

Replace the fuel regulator, and the rubber boots on the hard line going to the pre vacuum source putting vacuum on it. Also put clamps on the tube going to the crank shaft vent tube from the air box.

My transmission was shifting weird, and cruise control did not work exactly as advertised...this fixed it...the thing runs completely different.

Here is a vid of some guy doing it: https://www.youtube.com/watch?v=oa3E7ClI3Bw

You need a Torx T30 Socket, with a U Joint extension. I also picked up a 8 Piece Right Angle Screwdriver from harbor freight along with the torx tips that fit it. Made it really easy. http://www.harborfreight.com/hand-tools/screwdrivers/8-piece-right-angle-screwdriver-92630.html

PCV Crankshaft Vent Hose and Fuel Regulator Pre Vacuum Hose

  • PCV/Crankshaft Hose - 19.89 - pn: 24577310
  • Fuel Regulator Vacuum Line- 20.45 - pn: 12563356

Shift Cable Repair

DIY Transmission Flush

You have to be careful doing this...look at threads where people are burning up their transmission.

Steering Wheel Controls

Looks like you can put them on

Sway bar links and bushings

Well I put on a full set of MAXX END LINKS just before I went on vac to NC and drove down and back and around the mountain roads must of put on about 1800 miles and the didn’t beleave how different the TB drove!!!! A must do for anyone! Eddie!


Change sway bar links and bushings.

MOOG has blue hard rubber bushings that seem cool.

Installing Cabin Air Filter

I would have to cut the hole for mine and find a place that has that cover with the bolt because Part Number: 52489412 is Discontinued, which is the cover.

52494070 is not direct fit…can be modded?

Get one from auto yard 02/03 TB

Bezel/Cover on Side of Seat for Power Control Switch

  • Really make sure the part matches if you ever order. They have different size switches that clip in and the cover has to match yours.

Checking and Cleaning Grounds

Other Info Copy and Pasted Just Because

Figured it out. There’s 3 silver bolts on the rear fuse panel. They seem to connect the window and lock switches. Found out by accident. Tightened all 3 and everything works flawlessly.

Not for nothing, but I just installed new (additional) grounds from the battery to the frame and frame to the engine block and noticed very similar results. The truck seems to run more smooth and shift much more consistently. I also have no more dimming headlight issues.

When I was cleaning my grounds in attempt to cure the inherent headlight dimming issue that plagues a lot of us, I was kind of shocked to see how the main ground cable was designed. Mine was quite corroded in the open area where the frame ground connection was made to the actual cable.

I tried cleaning this area with electrical parts cleaner to remove the corrosion and that helped (did not cure) for a month or so. Since that helped, I decided to just add some more grounds to the system to see the effect. To my surprise, I was met with a very sweet running truck! About four foot of 1ga wire and a bit of time is all it took.

Anyway, hope this helps someone else.

This inspires me to try something new. I decided to clean the battery terminals and the two wire ends under the fuse box cover behind the battery with MAF electronic cleaner. It looked dirty enough to warrant some attention. It was easy and accessible enough. Put it back together after spraying some red anti-corrosion protectant onto the contacts. Holy christ the truck felt like it woke up another notch.

For what its worth, mine was slamming into second gear so hard that it felt a little shit was kicking the back of my seat every shift from first. It was an input speed sensor from the the motor to inside the trans behind the pump. The trans had to be dropped to fix the problem. One of the techs mentioned a TSB for it but I didnt get the #. Hope this helps someone…

forgot to update. i cleaned the maf out a few weeks ago when i first reported this problem. havent had any problems since. so im assuming it was just a slight bit dirty.

Rear Spare Tire

  • Check it and Lubricate the mechanism.

Ignition Switch

My car was shutting off sometimes...

Leather Seats

Honestly I may keep the fabric at this point. But you can get leather seats from another car and put them in. You can also integrate heated:

Front Differential Fluid Change

I got the synthetic valvoline with the additive already in it.

Rear Differential Fluid Change

I do not have a drain plug. I have to take bolts out, etc. I do not know, I would still take the entire rear pan off..even though this guy says that it stupid. I would want to put a new gasket on. I cannot have this thing leaking.

Front Drivers Side Differential Bearing

I looks like you do not have to drop it. But it looks like it is lubricated at all times.

I looks like for my application if there is no play in the axle that goes inside the differential, just check the seal and change it if it is bad.

If you want to Change Front Differential Bearing

Removing the Axle

Use a big drift with at least a 3-pound BFH on the tripot housing to get the circlip out of the splined coupling. No need to punch the shaft inwards first.

Removing The Outer Drivers Seal

Kept it from "drooling" fluid by jacking driver side up high (full reach of floor jack under frame). Kept the jack and TWO jack stands in there for safety.

Part Number For Seal: 14271618 - New part number: 19257296

Replacing the Bearing and Bearing Cup

Part Number for Bearing: timken carrier bearing that you may normally find damaged under the adjuster nut is JL69310 (outer race only, hand removable)

Once the adjuster is unscrewed, the end of the carrier bearing is what you see. The cup sides out leaving the bearing exposed for inspection.




"I did mine this spring, both carrier bearings were shot. it would be a compete waste of time only changing the one drivers side race, you need to pull the diff and do both bearings and seals, and maby even the pinion bearings, to set the carrier bearings it is a rotational torque of the input shaft. Doing that measures the proper preload, and if the one race is pitted those flakes are suspended in the oil and going through all the bearings and gears."

Front Axle Disconnect

Lets the front wheels spin independently. Frequently goes bad because the outer bearing in the unit gets dry and goes bad.

CV Axle Boots and Front Differential Seal and Possibly Bearing

  • Seal not OEM: SKF 15618
  • OEM: 19257296

CV Boot Clamp Pliers - 30800 Back

  • MOOG/PRECISION Part # 5445 CV Boot
  • MOOG/PRECISION Part # 5444 CV Boot
  • LISLE Part # 30800 Boot Band Pliers; Ear-Type Clamps

Clean (Simple Green, etc.)


Things you may need:

Replacement Small Inner Boot CV Clamp - 1.4 inches:

Dorman 614-068 - Dorman CV Boot Clamps

HowTo: https://youtu.be/-h_i-KOd4l4

Fuel Injector Cleaning


Stop Rust

  • POR-15

Audio System

http://diymobileaudio.com tweeters 2004 trailblazer

So, the Kenwood offers 4 chanels of amplification which are currently being used to power the front door and the rear door speaker pairs.

So, if you add a third pair (the tweeters), you will not have enough channels of amplification to power them.

If custom mounting aftermarket tweeters in the stock dash location is a priority, and you do not want to add an amp for the additional channels of amplification, you can install a component speaker set in the doors and use the separate tweeters as your dash pair.

wire to the front speakers, then back to the tweeters in the dash

So these tweeters do not have capacitors on them then.

They connect to the provided crossovers that come with the component speakers to ensure they only get the frequencies they are designed to produce.

Can you put two 6 ohms on a 4 ohm?

No. Any time you connect two speakers in parallel to a single channel of amplification, the resistance is cut in half. So two 6 Ohm speakers, wired in parallel to a single channel would present a 3 Ohm final load on that channel.

Wheel Bearing

Motor Mounts

Tip: I removed the two bolts that hold the top of the fan shroud in place so it would raise up with the motor. Otherwise, I found the fan would hit it and force it upward, causing it to start to crack.

Leave one in so the engine tilts

A post about 4x4 mounts: http://forums.trailvoy.com/showthread.php?t=65503&page=6
  1. http://gmtnation.com/forums/threads/main-wiring-harness-o2-sensors.11975/#post-329604
  2. http://www.gm-trucks.com/forums/topic/136704-trailblazer-and-envoy-cracked-exhaust-manifolds/
  3. http://www.itwpf.com.au/permatex/pdfs/approvals/7.pdf
  4. http://ls1tech.com/forums/generation-iv-external-engine/997949-equivalent-sealants-header-installation.html