I too have been working on a 2002 Trailblazer. No luck starting and the dash tachs freak out. I've done everything but changing the wires under steering column. I don't know.
My 03 Trailblazer starts great, however, the keys will not come out of the ignition, nor will it let you completely put the key in the stop position. Any ideas?
Master mechanic from Virginia here, with many years of GM dealer experience... & wanting to thank all the posters on this thread for... making me smarter! And now... to return the favor! (REALLY REALLY love this website!!)
Starting issues with GM vehicles in the 2000-2007 year ranges: biggest issue is BATTERY. If you've read this far, most every post mentions an electrical problem of some sorts. And the heart of any vehicle electrical system is the battery.
Most batteries last @ 5 years: AVERAGE. That means some LESS. If the battery in your vehicle is 4 years old or more, or you've had to jump start the battery more than once, replace it immediately, and could very well avoid having to deal with ANY of the problems mentioned in this thread. If you wait until you vehicle needs a "jump start" to prove the battery has had it... you've waited too long!!
Also note, jump starting many vehicles severely damages things right then: it's a voltage shock to the system. Being careful and "doing it right" isn't even much of a factor: it's the simple act of "forcing" high voltage/current through a compromised system. And you don't even want to know how many things you'll kill if you hook up the jumper cables wrong...!!!
AND... side post terminal batteries, as in most GM vehicles, are notorious for having serious acid contamination/corrosion IN the battery connections & cables, and which is usually never seen until the cables are physically removed from the battery; if the corrosion gets "into" the cable & the wire strands, it can actually wick, or spread deep into the cable and cause massive vehicle electrical problems; if the wire strands are yuck-green, the cable is a goner. Solution: replace leaking battery AND replace the affected cable (s.
Also, when replacing a battery (and checking the cables/connections as above), 2 more things MUST be done:
1) The alternator must be checked for proper voltage and amperage output, as well as for excessive A/C ripple: must have proper test equipment for this (most mechanics don't!!). Alternators are high failure-rate items.
2) The electrical system must be tested for key-off DRAINS. GM vehicles are notorious for this concern: you're not OLD (or bad otherwise) battery is dead, but the charging system is good: something is /killing the battery with everything "off", and the vehicle shut/locked. One of the faults for this concern is... that dreaded "ignition switch"... which can go bad or actually be installed wrong and cause a battery drain. Again... the ignition switches (electrical part) are EASY to install wrong!!
Here's a checklist then of starting issues: note there is a important distinction between starting issues (engine cranks or does NOT crank) and which almost all posters fail to indicate (most just say "won't start"...) :
NO START/NO CRANK:
* Many clicks heard at the starter, other vehicle electronics acting weirdly, and the engine won't turn over (crank) : dead battery (replace rather than jump; or remove battery & charge if it's still tests good).
* One click at starter, engine doesn't turn, all other vehicle electronics fine: usually a bad starter.
* One click at starter, engine doesn't turn AND lights go out while key is in start position: bad battery connection/cable or starter connection/cable.
* No clicks at starter, all other vehicle electrical stuff seems fine PLUS security light is NOT on or flashing when turning the key to the start position: failed ignition switch (electrical part).
All the above components can be replaced by any competent person at home, as long as name-brand quality parts are used...
Note there are FOUR (4) components to a late model GM ignition switch: transponder ignition key, key cylinder, lock cylinder with transponder receiver, and the ignition switch (electrical part). The transponder stuff is part of the vehicle theft deterrent system, and cannot be bypassed.
* Same as immediately above WITH security light on or flashing: theft deterrent problem: TRY ANOTHER KEY (the transponder chip in the key head may be damaged). If no go, tow to a GM dealer to fix the theft deterrent system.
* Key won't turn (but is removable) : try another key. If no go, tow to a competent shop.
* Key is stuck in ignition switch: call a tow truck and check the bank account.
For GM vehicles that won't start but TURN OVER
(No start/cranks) : usually fuel system/throttle body problems. First things to check are the air filter (replace every 20K miles max) and fuel filter (replace every 50K miles max). Complete Electronic Throttle Body failures are common (i.e GM 4.2 engines) : they cannot be successfully cleaned, AND cleaning almost always damages the fragile internal sensors and motors. In-tank fuel pumps give out after many miles of struggling to push against a clogged fuel filter, which on almost ALL American made vehicles (GM/FORD/CHRY) are waaaaaaaay too small (fuel filters) ; when replacing the fuel pump, always replace the fuel filter, even if recently replaced.
Good luck all!
Jeff-Shumway dot com
(don't forget the dash!)
One additional thing about GM electrical system concerns, and this applies to ANY MAKE modern vehicle: if you use any of the following equipment in your vehicle (other than stock/from the factory), you’re automatically asking for vehicle trouble, mainly electrical system faults: high power aftermarket stereos, ANY aftermarket alarm system, navigation interface, cell phone interface, laptop interface, portable CD or DVD players… basically ANYTHING that plugs into an accessory jack (“cigarette” plug), or anything that has to be custom wired or plugged in somewhere. Plan on replacing the vehicle battery & certain fuses VERY often… alternators, modules/computers, and maybe some wiring too… you’re now advised….!.
Jeff-Shumway dot com
(don't forget the dash!)
Have a 2002 TrailBlazer. Battery goes dead after 10 to 12 hours. Charging system reads 14.5 to 14/8 volts. All is shut off in the truck. You know, dome lights and such. Have taken a multimeter and measured a 1.5 amp draw. Which I know is too much. You should only have 20 to 50 miliamp draw normally. Have nothing on the truck that is not factory installed.
Now this is the catch. The elect on the back door, hatch back, rear wiper and washer and door lock will not work. I disconnected the main power lead to the fuse box under back seat and the power draw stops. Can't leave it that way and operate the car safely. Some lights and things won't work. Have disconnected every known fuse and relay to eliminate the battery draw. Nothing has stopped the battery draw. Except taking the main cable lead away from the fuse box. Really gone as far as I know to go. Oh I disconnected the alt. power leads and tested the starter for current that should not be where it has to be. Even millivolts.
Haven't been to a dealer yet. That is the last resort. Diagnostics at 80 to 90 $ hr can get real expensive real quick. Can someone help?