i own a 07 chevy blazer LS. diagnosed with the dreaded p0171 and the p0301. we basically changed/replaced the o2 sensor, spark plugs, coils, evap system, fuel filters, maf sensor, air filter, cleaned the throttle body and still the codes come up. it turned out its a leak on the intake manifold system. its hidden, not noticeable and a pain in the neck to get to, but once you replaced the gasket and tighten the bolts, you will appreciate your car better.

I must admit that is one of the best troubleshooting videos I have ever seen,, it's out in field.. you're doing it while it happens, it's not any fixed scenario back in the shop or classroom step one step 2 bullshit.... I just wanted to say keep up the good work keep those videos coming if you can you are truly a professional and this is example how the real world works... I know of a example almost like this where this gentleman has spent a great amount of money at dealerships trying to find a engine Miss over something just about what you shared with us.. over a year-and-a-half in a 2002 Envoy this gentleman has been over $2,800 trying to get a engine Miss resolved... dealership told him it was injector issue, then of course he went through this coil plug issue... then I suddenly had a vacuum leak on intake problem.. then also we have a fuel low pressure problem.. then what finally done it they told him according to the compression check. the cylinder was lower in compression than the others by 5 PSI.. and it probably has maybe a broken ring a valve issue.. and they would have to start by pulling the head off.. and that's where he said enough is enough... and said the hell with it so I guess he drove it for a few more months with ignition Miss off and on. anyway one day in the parking lot at work I heard it running with a miss then a couple days later it's running fine. so I asked him about it he said he's tired of putting money into it and I asked him if he would want to sell it.... he told me the story tell him to throw a number out there he said 1000 k I said what about $500.00 he said no. and I said 650.00 final offer.. we shook hands came to a deal... after messing with it for about a week lucked out .. found power supply wire damaged right up where it goes into the plug... it was not completely broken there was was a few strands still in tact.. sometimes it would miss sometimes it wouldn't.. went to salvage yard found partial wiring harness just clipped the plug and about 5 inches of wire off of it got it spiced and installed a new plug in #6. cleared the codes and fired it up and ran good.. no miss no engine codes.. decided to go ahead and put it up for sale had it detailed it finally sold for $4000.. now that's pretty good little profit but it's a nice vehicle could have got a little bit more I think but oh well with the detail, a free coil plug and $7 spark plug there's no more than $80 into it and a little bit of my time

learn so much from these videos

Finally, great how to video. Get so irritated skimming through YT video after video To just get more irritated. Much appreciated my friend I SUB 👍

Very Helpful..thank you my 2003 trailblazer has the exact same code..so now I can go to a mechanic & know exactly what should be done..thanks

Good show Terry ! I like that scanner you have, tells all and user friendly too... Nice fix and great tutorial for the folks here ! Stay warm bnrother

Very well explained process Terry. Thanks for sharing.

Good video thanks for bringing us along ended up doing all the inj. In my 5.3l took care of my codes see ya

makes things alot ezier to have a code reader thats for sure, good video brotha

Thank you for the clear and 2 the point instructions. Wish all videos were this straight forward. Could you make a video on this trailblazer and why the speakers are so sensitive to moisture and won't work for 2 days after rain?

Thanks for this video. I did what you said and I was able to isolate a bad coil.

Great video! We are clinging on to our 2003 Trailblazer because it has been a great vehicle to us but also...we are still enjoying a period of time without a CAR PAYMENT! However, I just got done doing a few things to this car thinking I have fixed it but it still has a problem. Our major problem was the car stalling in the middle of a turn on my wife. Well that went over like a fart in church for my wife which lead me to removing the throttle body and cleaning that completely and reinstalling. Also replacing all the spark plugs and boots. It seemed to run a lot better after that but seemed to still have an idling issue here and there. Very sporadic where it seems to bog down and then is itself and returns to a normal idle. We then had an issue with it giving us a flow during non Purge error code and a check engine light that would not go away... Also caused difficulty in starting after a gas fill up. This caused me to first replace the gas cap which resulted in no change. Then I replaced one of two possible solenoids, the first being the easier of the two which was the purge canister valve down by the gas tank (if I am saying that right for its description). That also resulted in no change in the check engine light... so the next repair that I performed was the replacement of the purge valve solenoid which is installed on the engine block... This solved the flow during non-purge problem and eliminated the check engine light.... The problem I am having now that I wanted to ask you about is that it still has a, I guess you would call, an idling problem. It has done this a few times now....yesterday it hesitated where it shuddered/shook and dropped rpm really badly upon trying to take off and then jumped up to normal rpm and ran fine the rest of the drive. Has NOT stalled completely since I cleaned the throttle body but still has these occasional/intermittent instances of bogging down and acting like it is going to stall and then goes. Very frustrating and the wife is ready to throw in the towel on this car...but I just feel there is something I am missing that is very simple. Aside from a transmission fluid leak this car has been a very reliable everyday driver. Btw it has approx. 150k miles on it. I have given thought to pulling the throttle body back off and cleaning it again apparently there is an air hole or something that also needs to be cleaned out that they say also helps to control idle which I thought appeared to be clean and i did spray some throttle body cleaner into but I don't know if that flushed it out completely or if that could even be what is xausing my continuing rough idle issue. Any advice you could give me to save us a car payment would be greatly appreciated! Thanks in advance! Peter

I find that often I'll have to push the plug on tighter to release the clip..Gotta love when a gadget can steer you in the right direction..Good vid Terry...My rule of thumb is "change 1 plug...change 'em all"...But a good vid on how to..I was hoping you would show how to isolate a cylinder by disconnecting the coil trigger wires one at a time...The codes would still have to be cleared but..Good thing with a scanner is we can eliminate mechanical problems from electrical problems...I sometimes rely on the old fashioned experience before I run a scan....Sometimes I'm correct..!!...lol.

Good fix terry always like your how to vids I really like that snap on scanner take care buddy

Great video, very helpful

Good troubleshooting Terry,

Nicely done. Live data from the Snap-On scan tool is great.

Take the airbox off, start the truck, unplug 1 coil at a time from front to back, the one that did not change engine idle is the bad one. no scanner needed, very common problem. if you own a trailblazer, keep a couple extra coils on hand.

2:57 I use a small screw driver to remove those I just pick the bottom of the plastic clip, lift "carefully" then it remove the plug freely without using too much finger strength :)

Thank you so much very good video.and you did a good job explaining what you was doing.

I do not have that Snap On. What were the resistance measurements of the bad coil respect to a good coil? 1. Resistance measurements in circuit? 2. Resistance measurements out of circuit? 3. Resistance of rubber insulator (plastic post) to ground? Wonderful tips, thank you.

I changed the plugs in mine and it had a misfire on # 5 cyl .When I bought the plugs at Napa there was a full box of four plugs and 2 singles .After examining the boxes one had a different barcode lot # same plug different lot .Cleaned my old plug replaced and it runs great .Always make sure the plug has the same barcode #. Not the first time this has happened

Very nice video thanks!!!

thank you for this video, and also the walkthrough on it. big help

Good fix Terry. thanks.

Thank you for this. I have a friend three hours away that has a P0301 and I tried explaining it to her but this is better. At least now she knows what to expect when she takes it to a mechanic.

That number one seems to be a issue with those, that ac line above drips water on them. I've even seen number one full of water and the rest are dry.damn 5 cylinders.

nice

I have an 03 TrailBlazer with over 200k. Havent had to do much to it till now,everything is starting to fail at once. I have always maintained it as far as oil changes,filters and other things. Being it has so many miles on it now,I am thinking its time to dump the old girl.

Short and sweet thanks.👍🏻

Hi, I had one question: how do you remove the white clip that holds down the plastic wire tray? Do you pry it up or does it turn counterclockwise like a screw? Also it was a great video, nice work. Thanks.

Well done - it gets real interesting when the fault doesn't move and a new plug and coil doesn't fix it either. Every time I work on a farm truck not used all the time the first thing I check is for mice damage. I was working on one yesterday and after the poor old guy replaced two alternators he goes to the local garage and they charge him $60 to tell him this new alternator is defective as well . I had to rewire a whole new harness to the alternator. All but a couple of strands of wire were left and of course you would see the correct voltage but you couldn't even light a test light. Do you see mice damage down your way ?

Smashing video :-)) Thats one dusty/mucky engine, the new coil pack makes the others look really filthy. The obd tool is a must isnt it, snapon isnt cheap but im sure its capabilitys in comparison to cheaper units make it indispensible :-) I would be looking at the sparkplug tip colour and hoping i could see which one was different, but the odd annoying misfire i suspect would not fowl up the plug good enough for a visual diagnosis.

That scan tool sure takes the guess work out of it.

Oil in the plug holes is caused by loose coil pack bolts...

So if it were the 4th one (p0304 code) would i switch to the first to test or 3rd?

I know this is an older video but thank you, regardless.. How do I know if my boot is nad on my coil pack?

Hey I'm having the same problem each time i turn the truck on it rattles. Its good for about 5 miles but once i come to a stop, the truck shuts off. I replaced the spark plugs to 4 out of 6 and its still has the same problem. Im waiting for new coils to come in. Once I replace them I'll post the finding. Thanks for the video.

I know this is 8 years ago but I’m having this problem I replaced all the spark plugs and replaced the first coil thinking that be the problem unfortunately wasn’t what could be the issue

nice fix

thanks for the vid, mine is misfire on 3 so it will be easier. lol

I have same make and model trailblazer went changes plugs cause just bought couple months ago been running fine noticed wire on very back plug was unhooked lose plugged back up ride will crank won't start please help

Really helpful!

great video ...trains comming

me alsoi t was darn near perfect thanks im working or helping on a similar SUV stuck in the fields oh boy

Does the service engine light blink?

another question for you, I have the Launch Creader VI code reader, would you recommend anything else or is this reader fine? It gave me this issue PO303 and when I had my secondary emissions issue code PO410, just wondering if I should get another, my shop guy uses this and another as backup !

My 2004 Trailblazer had a misfire on #4. I replaced the plugs and the #4 coil. The issue is now I have multiple misfires with a flashing check engine light. I sprayed the throttle body and wipe it off/out best I could and this did nothing. The trailblazer seems to be running on about 4 cylinders. Any advice on what else to check. The truck is simply unusable at this point and I would like to get it running without spending money for chasing ghosts. Could the cam be bad? the mileage is 110,000 Plugs are OEM replacements. New coil is autozone branded OEM replacement. Autozone say maybe the new coil is causing the other ones to not work right, but I feel this is a sales pitch how could multiple coils fail by replacing one coil

I had a p0302. I swapped coil number 2 and 3. Now when I check it it's giving me the random p0300. Any ideas?

Had this same problem on my 03 Trailblazer. Did what you suggested, switched two of the coils around. It seems to be running better but now I am getting the general misfire code P300. A friend suggested changing the coil packs in order of the firing sequence. What would you suggest I look at next?

Just to be clear. The #1plug is in the back, 4 is in the front

I switched 3&4 coils out, and it went from 3 to 4 for misfire. So do you think that while I'm in there, I should just go ahead and change everything, plugs and coils, to not have to worry about it anymore? And are the cheaper coils on Amazon worth using, or should I get the Delphi coils that are meant for GM? I.ines an 03 trailblazer.

I like this kind

Just did A spark plug job it started up fine with the new plugs but misfiring so I decided to put the old ones back in because I figured the new ones were faulty. So I put the old ones I and now it's crank no start? WTF JUST FROM PUTTING INTHE OLD PLUGS. So I then took out the old ones and put the new ones back just to get it started and it's still NO CRANK NO START.

I let my truck run and I unplugged the ignition coil wire #3 and the truck didn't miss... But the other coil wires... It missed when I unplug them .. I think the ignition wire needs to be replaced... I might get another harness or splice some wires from the other trailblazer I have setting up

Firing order 153624.... Is that not #5 you unplug at 6:26

when in went into these soft grassy slippery hills it was a hiccup as its powerless now wont idle cannot get back up on its own wich in turn in a rural setting would make it useless maybe a kinda safari SUV still it has yet to show dependability -so boss says it comes out on own power or else hee haw been down there 3 weeks

Not sure what you were doing, but it was interesting. ;0)

No Doubt mine is fuel issue specially running out of gas where do I stand ?

Had same problem with my 2004 Envoy. Turns out it had an oil leak into #4. Fouled the plug and shorted out the coil. Mechanic said it would be $500 to replace the valve cover gasket. Gasket only $28. Because you have to remove so much off the top, lots of time. Any way to seal around that socket to keep oil out?

My 07 Envoy 4.2 has p0300 and p0306. Has150k so I Changed plugs and came across #3 wet with oil and oily plug. Was able to clean out with detail attachment on shop vac. Don’t have scan tool so will run and use parts stores to reset codes. If theirs oil on my plug it’s bad head gasket. Is it okay to drive with it leaking & or can it cause other damage? Awesome video

@wtbm123 I have a 2005 trailblazer and it's a project car. when I bought it it had codes for pcm, misfire on cylinder 3, vss and fuel level sensor. I fixed most of them by cleaning the throttle body and tightening the loose ground on the drivers side fender. Now the car he a slight misfire on cylinder 3. I bought a new plug and swapped the coil and the cylinder is still dead. Also my obd2 port isn't responding but it has power. The cigar fuse is good too. I could care less about the fuel level sensor just need to get ride rid of this slight misfire. Any suggestions?

What about a random misfire 06 trailblazer did the plugs did the vvt

What would cause coil pack#1cyl to fail repetitively? on third pack 2nd spark plug. Thanks.

Hey I've a question...and I'm trying to determine why my 2002 trailblazer is not starting up. I've tested all coils one by one and initially only two were sparking after some more testing, now none is sparking but they all have power going to them. But my question is: how many ohms should a new coil test for A B and C wires? Thank you

how do you take out the boot/ cords? we did what you said and #1 still misfires.

My trailblazer has cylinder 6 misfire which makes the truck jerk and i changed the spark plugs but the check engine light is still on. Do I have to erase it or do i need to fix something else?

Which brand of coil would u recommend,rock auto sells different brands and prices,I'd hate to order one coil just to find out it doesn't fit!!

If I have oil in inside the coil with the spark plug what kind of problem do I have

I have a Chevy trailblazer 2005 I have a code p301 and I change spark plugs but I find oil on spark plugs What could be the problem Help please Thank you in advance

Ya don't need to put it back on or any of that...just start disconnecting one coil at a time...if the idle doesn't change then the coil is bad.

Good video,I also got an P0301 on my 05 Trailblazer and I did swap out 1 in number two's place and erased the code but for some reason instead of the code P0302 coming up I got P0300 instead why do you think that happened?,I even changed the plug with a new one of the same type.

very cool........tony

Have a 2003 envoy 4.2 that keeps giving a cylinder one misfire. I've changed the out with three good coils and changed the spark plug everytime as well. Still getting the cylinder one misfire. Any other suggestions?

Hello, I have been working on my 2002 Trailblazer code P0301 misfiring cylinder #1. I've replaced the ignition coil but the problem hasn't resolved. What other problem could it have? I would greatly appreciate if you could give me an idea of what other problems it might have. Thank you.

Great video for explaining how to check to be sure, thanks, what should a GM coil cost ? my guy says $240, sound high, what do u think, thanks

A lot of times u will find oil draining on plugs get ya some engine puty spread around seal

What kinda scanner is that?

I have p0301 , so I switched coil to cylinder # 2& now it reads p0300 , any thoughts . Engine is really shaky 🤔

How to tack a scur if you burak the scur

Front to back is #4.3.6.2.5.1

I just had to have a coil replaced in my 2004 trailblazer. Not sure which cylinder it was

Cool

I'm no coilologist but according to facebook it might be bad

A good mechanic would have at least pulled the cylinder 1 plug and inspected it, the number one cause of failed ignition coils is worn spark plugs, and you put an old coil on top of the plug that was not firing, it's OK for diagnostic purposes but I wouldn't have shipped the vehicle like that, that's just asking for a comeback.

Mine turned out to be zero comprehension on 3

Well... In my car I swapped 5&6 and got a misfire in cylinder 1

Ford trailblazer really bro, wtf. That is what i heard! Lmfao

Where did you get a 5 cylinder Trailblazer? Ha!

My wife's car is the same thing, same thing happened to her's And I did the same thing but I also changed the plugs,And let me tell you that last coil and plug was a pain in the @ss to change.

For my 2000 Corolla, a set of 4 coils was hardly $100 and a set of 4 platinum plugs was $30. And the savings over a garage doing it easily was $200-250. Do the basic stuff for yourself.

Often times it ends up being worn out valves/seats and needs a valve job....and good luck getting the head off without the head bolts breaking off in the block. Junk ass GM.

Very well explained process Terry. Thanks for sharing.

Great video. Very helpful