P0412, P0365, P0366 Cranks But Won't Fire

Right before the pandemic I got raped by Ware Chevrolet in Blairsville GA. It was one of those cases where I kept calling in and kept them appraised that if the water was getting deep, I wanted to know. They kept saying know and then one day the service mgr told me "We had to open a case with GM. The techs don't know what the problem is."

Well, pandemic happened. Survived.

Some natural disasters and work happened.

I have been told that because the truck won't start, won't run and continually pulls the P0412, P0365, P0366 then I am screwed- that the cam needs replaced, the plastic VVT shoes,. These are actually new codes.

When last I was working on it a month ago, decided to check out the gas tank.- with a digital fuel pressure gauge I was getting no pressure. As a result, I dropped the tank and I saw horrors that no man should ever see. So I replaced my gas tank and put in a new fuel pump. It was not a joyous occasion as I do not have a lift.

Here is the last time the vehicle ran:


Here is the last time the vehicle fired off:

It would fire these last times and then there seemed to be a back fire and

The very last time it drove home it was stumbling and I was afraid it would shut off at idle. I have a digital fuel pressure gauge and it was showing poor pressure, I want the thing reliable, so I said

The only codes that the vehicle pulls with my Tech2 and with my ELM327 are P0420, P0365, P0366.

I replaced the upper cam sensor.

Research has told me there is an actuator sensor that can respond poorly to dirty oil. At this point, I cannot say for sure when the oil and filter were last changed- so it is indeed a possibility I need to do that.

It cranks over strongly now. But no fire.

Thoughts on how to proceed ? Change oil and filter, remove and clean throttle body and replace the cam actuator sensor ? Sound like a plan ?
 
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Mooseman

Master Blaster
Moderator
The two cam sensor codes are very specific to a wiring issue. Check the wiring since you already replaced the sensor. There is no reason to suspect the CPAS or the cam phaser yet. The wires can get damaged right at the plug because it's pretty exposed there at the sensor. If it checks out there, check for continuity from the sensor plug to the PCM plug. Check the schematics in the manual (link in my signature).

P0420 is a cat efficiency code. Might be because it's running like crap or it actually is borked. Will not affect ability for engine to run properly unless it's also plugged.

I have a digital fuel pressure gauge and it was showing poor pressure,
That is likely the reason for the poor/non running since it can run without the cam sensor. What are you getting for fuel pressure? I'd fix this first to get it running.

BTW, be careful with the fuel pressure test port. It's in an awkward position and my tester's adapter put pressure on it at an angle and cracked the base of the port. Had to replace the whole fuel rail.
 

2006TB42Nightmare

Newbie
Thread Starter
Dear Mooseman, my computer went to sleep in the drafting of the original post. When I got the laptop back open I didn't check that all the revisions I made were clear.

I have completely replaced the fuel tank and the pump/filter combo. The crap in the tank from Wares letting it sit would just not come out. So I went and got a tank and I ordered an AC Delco or Delphi fuelpump and filter. Replaced all that.

It was stumbling and seemed like it wanted to die at idle the way home from Wares. So I started checking the fuel pressure.

Went from getting 5psi or nothing to 19psi that video where it was last running.

After replacing the tank and the fuel pump I am getting 54-56 PSI.
So I have good fuel pressure now.

By borked you mean the catalytic converter could be bad ie completely screwed or did you mean to type blocked ?

This is the cam sensor I have replaced: Trailblazer Fuel Pressure Sensor.jpg




I have been told that I need to replace this guy by a guy who worked for a Chevrolet dealership. He says if I replace the VVT sensor below the chain is broken or the VVT mechanism is messed up. He was the guy who recommended an oil change and filter change.
Camshaft VVT Actuator Sensor.jpg


THANK YOU BROTHER MOOSEMAN !
 

2006TB42Nightmare

Newbie
Thread Starter
I have continuity from the ECM to the Camshaft Positioning Sensor. Tested it with my Fluke meter.

Any thoughts from where to go from here ?

Checked I have continuity at CPS to the ECM. I have a Fluke and also checked it with my backup multimeter.

I have 54-56psi fuel pressure.

Cranks over fine, I have fuel pressure.
 
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quote: " have been told that I need to replace this guy by a guy who worked for a Chevrolet dealership. He says if I replace the VVT sensor below the chain is broken or the VVT mechanism is messed up. He was the guy who recommended an oil change and filter change."

what does this mean? Have tried doing some compression tests to verify "mechanical sanity". Having said that, as suggested the codes seem more electrical than mechanical. How are you doing your continuity test? At the pcm connector, disconnect, and measure across two pins in question (eg. 12v to low ref, signal to low ref) WITH the connector in place at the CPS. It should read something. Go from the result. Have you pulled the VVT actuator to look at it to see if it is damaged?

further: have you tried spraying in starter fluid during a start attempt to see if things will start... careful especially if you are seeing backfires... which perhaps indicate a timing issue.
 
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MRRSM

Lifetime VIP Supporter
An Echo from Post #2 from @Mooseman 's Advice...

Having replaced the CPS (Camshaft Position Sensor) for the P0365 and not solving the problem...the P0366 steers you toward checking out the integrity of the CPS Harness VERY carefully. The CPS is the final arbiter telling the PCM what the ACTUAL position of the Exhaust Camshaft is in vs.whatever the CPAS does with VVT "Variably" moving the Camshaft under certain condition over the narrow fore and aft motion region of 0 to 25 Degrees.

The PCM also uses the CKP ( Crankshaft Position Sensor) to work together with the CPS to determine WHEN to Inject Fuel through each EFI and then Time and Fire the Spark Plugs.

The fact that you have the two closely related CPS Codes occurring at the same time should encourage you to also check out the entire length of the CPS Harness from where the wire attachments mate up to the CPS Connector as far back as your Flashlight and hand manipulations can work to make this examination. Consider the possibility of having Rodent Infestation Damage to your Engine Wiring Harnesses.

As for the P0412 Code... This Video will cover the Whole Story concerning the rash of PXXXX Codes relating to the SAIS Pump Design and refer to a TSB about that problem. THIS Code is entirely secondary to the "Backfire" Problems and can be addressed after you manage to get the Motor to Start Up and Stay Running:


If you were having problems with the CPAS unit... you would see a related Code getting thrown as well (P0014). so replacing the CPAS at the moment is probably not necessary. But again, Unbolting the Three Fasteners to remove the Power Steering Pump, then performing a CPAS R&R with Good Solvent Cleaning of the Debris Screens, and checking that the CPAS Connector is NOT saturated with Engine Oil is still a good idea. If you decide to do this part, make certain to Change your Oil and Oil Filter at the same time to avoid getting the CPAS Screens "Re-Clogged" with Carbon Junk, etc.
 
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2006TB42Nightmare

Newbie
Thread Starter
Question: Is the pigtail for the camshaft position sensor for a 4.2L going to be a salvage yard only item ? Thanks very much, all.

I am trying to figure out whether to junk a vehicle with 54k miles on it, excellent suspension, excellent transmission, I replaced the hard transmission lines when I replaced the gas tank, fuel pump and fuel filter assembly(2006+ it is one unit- pump and filter).

I don't want to overreact but wiring was what Ware's reamed me for. On the underhood computer they rewired the center connector to 2005 and previous style connector. I'll try to get pictures. They said they could not get the ECM to communicate. That was not my experience with my Tech2.
 

TollKeeper

Gold Supporter
Something is telling me you have a fueling problem still. Dont know why, and I have no basis to make this claim. It just seems to fit the scenario.

I would do, as suggested above, pull the air filter box up, spray some starting fluid in the intake, and try to start it.

Also, be sure to make sure the MAF is fully plugged in, and seated. Many people have had issues with engine stumbling, and poor running, because that plug was not seated, or completely unplugged.
 

MRRSM

Lifetime VIP Supporter
No. You should be able to buy a GM OEM Standard (3) Wire Hall Effect Sensor Metra-Pack (Silicone Weather-Pack) Harness Pigtail by searching over at RockAuto or even on Amazon using the factory OEM Part Number.

You seem to be a long ways away from having exhausted all avenues worth investigating up to this point. With so much 'Effort and Coin" invested so far in what should otherwise be a Very Decent Project SUV... having it crushed at the Salvage Yard now would be a very sad and wasteful outcome.

Has this SUV ever been involved in any Accidents or Floods? Running a CARFAX on it would be a worthwhile investment to find out for certain. Knowing WHERE this vehicle was being driven during certain its lifetime near Major Weather Events will clue you in about the possibity as to whether or not this SUV has ever been submerged under water and re-built as a Salvage Vehicle. Has this Engine been replaced with one having a DIFFERENT Crankshaft Reluctor Ring Notch Count vs.whatever the Original PCM was happy with and thus... making them fight with each other?

In addition, it would be helpful to know whether or not the Prior Owner had performed ANY under-hood re-wiring for either a Security Alarm, Remote Starter or any other After-Market Devices of ANY kind that might have involved tampering with the Factory OEM Harness.

You COULD try getting your hands on a COMPLETE Used Under-hood Engine Harness specific to your Year-Make-Model vehicle and try working out that solution out as well. Generally, eBay has a quite a few available to choose from and they tend to run anywhere from $100 to $250 for the 'Whole Shebang".
 
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Mooseman

Master Blaster
Moderator
If continuity from the CPS to PCM has been verified at each relevant pin, what about shorts, either to each other or to ground? You could have two chafed wires shorting on each other somewhere. This has happened, although not necessarily with the CPS wiring, in the middle of the harness inside the plastic loom.
 

2006TB42Nightmare

Newbie
Thread Starter
I had other things I needed to do Saturday and Sunday. Instead I shot Saturday and went and looked at a couple of complete harnesses and they were worse than what is under my hood. The kid working the parts counter in the service dept at the local Chevrolet dealership had no idea how to look up what I was looking for, and I even said- find me an NOS 2006 Trailblazer 4x4 4.2 Vortec engine wiring harness and I will pay now. Then I asked him for exactly what Mooseman specified and his jaw JUST dropped- he had no idea what I was talking about much less what I was asking for or how to find it.

The only accident was by Ware Chevrolet when the vehicle was new. We bought it as a "demo" in 2007 with less than 2k miles on it. When we got it, it was state law they report to us if it HAD ANY accidents. They said no. Well, later when my father and I were going to sell it, we had the TSB for the door wiring fixed at the same dealer I stopped for parts at. Before we ever were going to offer it for sale we decided to see if the door fire threat was on the CarFax because quite a few people actually asked "Is it going to catch fire ?"

So we looked and much to our surprise it had what they said was a minor front end collision. Then I got to thinking about it, and I said why would it say minor if several of the OEM stickers on the underhood are missing ? So I wanted to get the pumper repainted and get the valance replaced. Took it to a body shop- by no means was it minor collision.

We live 5-7min drive from where the owners of the Wares live, my father has known them all their life, the previous owner handed it down to his son in law, the s-i-l is a "business first" guy. So even when the Trailblazer repairs ran to $3k when we had only authorized them stopping at $1k and hauling it home, even when they put a $200 battery on it that failed in less than 2 months because it was so old and that they refused to warranty, and even when it stuttered leaving the dealership $3k in the hole but "fixed"- my dad was in denial because he is in his early 70's and he has known all but the current 20-something and early 30's kids all his life. But this has hit him hard because I bought everything(a pair of Tech2's and a dedicated Thinkpad T30 to run the serial port and Tech2 software on) and it has finally warned him off.

If I could fix it, we have owned it since no more than 2k miles. My mother who has a pretty good memory for such things says we bought it with 1,200 miles on it, slightly over the 200mi part of 1,200. It was once a very well beloved vehicle. The sad thing is my mom believes once any vehicle hits 60k miles it must be traded in, shot and buried, sold, burned at stake, you get the idea. We had a 2005 we bought BRAND NEW and my mom badgered my dad into selling it in 2007 because they traveled a lot and they loaned it to my sister who was going back and forth to academic conferences.

I threw in with dad on this 2006 when mom got him to sell the 2005. The 2005 has 200k+ mi on it and the paint is crap but I still see it around. So if caving to my mom hadn't happened then possibly then this wouldn't have all happened.

I know it was the last Chevrolet we would or ever will buy.

If there were a reliable way to get the kind of gas mileage the 4.2VVT got and do an engine swap, and no have to deal with the amount of underhood testing I've done on this vehicle- I would gladly do so at this point.
 

MRRSM

Lifetime VIP Supporter
Step back away from ANYTHING Electrical just for the moment, and let's look closely at Post #5 where @budwich suggested that this odd issue may STILL involves being a Fueling Problem. Try taking a Hard Turn in that direction even if for no other reason than to eliminate this possible problem area.

Try doing The Basics he has suggested:

AIR...FUEL...SPARK

(1) Obtain a Decent ABC Fire Extinguisher and park it nearby...
(2) Pull Out the Fuel Pump Relay...
(3) Have a "Helper" sitting in the Driver's Seat...
(4) ...while You Spray Short, Controlled Bursts of Starting Fluid...
(5) ...as the "Helper" begins to Crank Over The Motor.

If the Engine Fires off and RUNS ...even if only momentarily... It will PROVE that your Ignition Switch, Ignition Wiring, the PCM Harness and the CKP Sensor are all WORKING and will at least allow the Engine to TIME and FIRE OFF with an External, Unregulated Fuel Source.

IF this occurs...it puts you back in the realm of investigating EVERYTHING from the Fuel Tank forwards to the Fuel Rail again...including the Fuel Rail Wiring Harness.

You are among Friends here who have stood in your Shoes on many an occasion; Shaking Our Heads ... and yet still willing to keep on trying to "Work the Problem Using The GMT Nation Hive Mind" until we can Figure this Damned Problem OUT.
 

2006TB42Nightmare

Newbie
Thread Starter
Gotcha. I'll abandon the issue of the underhood wiring and make sure to run a triple check tommorrow on the fuel pump. I have ether that has extra top cylinder lubricant to try to insure the ring lands don't get damaged I will spritz and have Dad try to turn it over.
I have a Kent Moore fuel pressure test kit, a digital fuel pressure gauge I bought from Snap On with a number of adapters, and I have Deutz-Allis starting fluid with the extra protection against ring land damage.

I appreciate the help greatly.
 
clear your codes before your attempt at "start with starting fluid".... IF the thing doesn't start, check for codes there after. IF they come back, it is likely you need to do some "good / directed" testing around the those codes (ie. cps and vvt actuator).
 

2006TB42Nightmare

Newbie
Thread Starter
Well. I cleared all codes with the Tech 2.
My dad turned it over before I could begin spraying ether and it fired off with no backfire but only for a few seconds, and then there was the faint odor of unburnt gas.

Cleared codes, lightly sprited D-A starter fluid. He turned it over. Cranked over fine. It popped off and ran(combustion) for the longest it ran since I drove home but it had a small backfire and died.

He tried again and no luck this time. Nope. No siree. Bob. Cranks fine, no fire.
What are the codes ?
P0412
P0365
P0366


Didn't want to run down battery. Got down to 30's last night. Took battery off. It is charging.
 

2006TB42Nightmare

Newbie
Thread Starter
When I say no fire, the engine turns over, will fire off with starter fluid but it runs and dies.

It continues to pull
P0412
P0365
P0366

I bought an OEM Camshaft Position Sensor Plug/Pigtail and 3 wires from my local Chevrolet dealership. $85

I could not find one on Amazon to match my CPS plug or one that would interchange for sure with 4.2 Trailblazer

Underhood wiring harnesses are all sold out for 2006/2007(they apparently use a common one) but I know from experience 2005 and back is different in aspects, and I have worked on a later 2007 model and I know GM made a change there as well.

At this point in time, I am doing the best I can. If I had been able to find a pigtail cheaper, I would have.

I AM VERY HESITANT TO SPEND ~300 on a 2006 wiring harness off Car-Part,com or Ebay(that is going price with shipping and SALES TAX) because it will be 14 years old.
 
pull the vvt actuator that you pictured and visually check it. These are known to have problem when there are issues with "oil cleaness"... regardless of whether you change the oil.

do the resistance check that I suggested earlier... that will check both sensor and the wiring. Go from the result.
 

Mooseman

Master Blaster
Moderator
There is an obvious problem for the circuit/wiring to the cam sensor. You have to completely verify the wiring from the PCM to that sensor as I indicated above. A broken or chafed wire anywhere in the wiring loom can cause this. You might have to unloom the wires from the cam sensor to the PCM to find the short or break.

Ignore the P0412 for now as this is for the secondary air injection system (SAIS) and would not affect the engine from running.
 

MRRSM

Lifetime VIP Supporter
Agreed on NOT spending Money via a Mere Guess on my part...

But perhaps you can use this Schematic to Wire Trace your in-dwelling Harness CPS Circuit to and from the PCM and Test it all for Continuity with a Lighted Probe and a DMM ...while your Dad Wiggles the Harness around for EACH involved Test Connection:

trailblazer-camshaft-position-sensor-wiring-diagram-to-pcm-7.gif

....one more idea... Visit THIS Link and use the imagery to Locate, Remove, Clean and Re-Attach ALL of the Engine Grounds:


To aid in identifying the CPS Wiring Connections at the PCM side, here are the images of All Three Identical P-10 PCM Wire Harness Connectors... with the "Locus In Quo" being at the "C2" Image as shown on the above Engine Sensor Wiring Schematic:

GMP10PCMC1CONNECTOR.pngGMP10PCMC2CONNECTOR.pngGMP10PCMC3CONNECTOR.png

If a Short Circuit does NOT reveal itself during your Testing of the CPS to PCM Harness Circuit... the possibility of having a Failing PCM should be considered as well.

Transposing any PCM from this same Engine and Transmission Era from a Salvage Yard will reveal if this at is the heart of the problem... and since you have your own Tech 2, re-programming an inexpensive Junkyard P-10 PCM should be very straightforward, as long as your Battery has a FULL Charge and any other Modules, AC or Radio, etc. are NOT on and functioning when you install a New Calibration.

By the way... Have you done any PCM Programming Updates yourself on the OEM PCM in this Vehicle?

 
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2006TB42Nightmare

Newbie
Thread Starter
Thanks everyone. I am going to catch up on some work in the shop. Once I have that straightened out and the money tree bloometh(can't get paid if you don't do what you are supposed to)- I will be out there again. It just probably won't be today.

I have a guy who can come help me with the jiggling of wires, it has gotten cold in the NC mountains and my dad is in his 70's and not feeling well much of the time.
 
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TollKeeper

Gold Supporter
I would have to back the train up for a minute.. Putting aside the engine codes for a moment.

You got it to run on starting fluid. It should run, and be able to give live diagnostics, via a regular engine start.

There is still a fueling issue going on.
 

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