NEED HELP 2004 Trailblazer - initial code p0300

mgbspeedy

Member
Just joined the forum today after watching a few of MAY03LT's youtube videos. 2004 trailblazer 4.2. was driving and lost power. (unable to go above 2500 rpm) engine light started blinking. pulled over, and towed home. Initial code was p0300. In the past, Ive had p0302 etc did some tests, replaced coil. Problem solved. This time. Similar tests came up blank. Searched for vacuum leaks. tested fuel pressure. Tested throttle body. Found throttle body motor was bad. (there had been chattering at 2500 for a long time, so I wasn't surprised) Replaced. Watched videos on the subject. I had pulled the number 10 and 28 fuses while doing the work. Not much difference. Still throwing p0300. Found another video stating similar issues and a quick check.
The video is rough watch even though it is informative. (Summary-the fuse box mounts were loose) I did have one loose. The bolt housing was loose, but the bolt was difficult to turn. (tight when it shouldn't be) I did turn it in. (everything snug) Started engine and all kinds of new codes were thrown. Here's the list - P0215, P019, P0234, P0357, P0443, P0736, P1143, U0001, U0101, U0106 And then started acting like a bad battery. Even reset my clock. When I'd turn the key to ignition position but not start, the interior lights would dim. Loosening the bolt, helped with the lights dimming, but not the codes and battery appearing dead and starting issues. I'm worse off than I was before. Could a short be the problem (p0300) all along? Any help is greatly appreciated.
 

Mooseman

Moderator
You sure these codes are from your TB? Some of them are for stuff not on this vehicle like turbo and glow plugs.

For the P0300, best would be to use a scanner or a Bluetooth adapter with the Torque app to monitor misfire data to see which ones are misfiring. How long did you run it with the misfire? It usually takes a while for it to go from P0300 to a specific cylinder.
 
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mgbspeedy

Member
You sure these codes are from your TB? Some of them are for stuff not on this vehicle like turbo and glow plugs.

For the P0300, best would be to use a scanner or a Bluetooth adapter with the Torque app to monitor misfire data to see which ones are misfiring. How long did you run it with the misfire? It usually takes a while for it to go from P0300 to a specific cylinder.
Thanks for your time.

Sorry. Looks like first 2 codes I listed are typos. Should be P0125 and P0196. I was reading them off of a picture of the scanner I took on my phone.

re: P0300 and torque scanner tool app - at this point P0300 isn't even throwing.

Only the codes I listed (with exception of the 2 corrections of typo) I think there is a bigger issue of a short, bad ground or PMC problem. Although I'm willing to buy a new scan tool, or WIFI and phone app, once I get short issue worked out. Mine is old PC laptop.

re:How long did you run it with the misfire? It usually takes a while for it to go from P0300 to a specific cylinder.
I initially only drove it long enough to get off the road, as the engine light was blinking. (Didn't want to ruin my CAT) I think it's also important to be clear that is running far worse then a specific single cylinder that is misfiring. I've had that before. code was P0302. It was an easy fix. That was over a year ago. After ruling many things out for the P0300, my next test was going to be to look at back pressure, but everything went haywire after the fuse box tighten. Need to figure that out first and hopefully get back to where I started. Although, now I'm wondering if the initial trouble may be ground fault related. Any thoughts on the shorting or faulty ground connections? Thanks again for putting in time. I'm 50 and have rebuilt engines from the 60's, but these computer cars are a little over my head.
 
D

Deleted member 20902

Ignition switch is a common failure item that can cause strange codes like this. Also sometimes the plug for the throttle body is difficult to seat, try removing it and reseating it. Clear codes. Then go from there.
 
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mgbspeedy

Member
Ignition switch is a common failure item that can cause strange codes like this. Also sometimes the plug for the throttle body is difficult to seat, try removing it and reseating it. Clear codes. Then go from there.
Thanks. Is there any way to test the ignition or bypass to see if that's the issue? Or is it a swap parts and see what happens kind of deal? I'll, of course start with checking connection to throttle body first. We are in the middle of an ice storm and I don't have a garage, so it will be tomorrow before I can get to it.
 
D

Deleted member 20902

The ignition switch is very easy to remove, you can easily pop the covers off and it will be quite evident if there is a problem there. It's also possible to clean the connections with Emory cloth, and put some dielectric grease in all of the contacts. That is, if it is not too far gone. It's a $35 part at any parts house, just be sure to check the box before you leave the store. It's extremely common for people to bring back their old parts and they are not usually checked and therefore restocked.
 
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mgbspeedy

Member
The ignition switch is very easy to remove, you can easily pop the covers off and it will be quite evident if there is a problem there. It's also possible to clean the connections with Emory cloth, and put some dielectric grease in all of the contacts. That is, if it is not too far gone. It's a $35 part at any parts house, just be sure to check the box before you leave the store. It's extremely common for people to bring back their old parts and they are not usually checked and therefore restocked.
Replaced ignition switch. Also sprayed the PCM and fuse box electronic connections with QD Electronic spray and charged the battery back up while it was disconnected. Back to my normal P0300 where I started.

So I haven't checked for back pressure being an issue yet. Was going to do that when everything went haywire.

Was going to remove the upstream sensor, or slightly loosen the CAT bolts from the front to see if I notice a significant difference in power or misfire.

Any other thoughts on the original issue - loss of power - Limp mode (RPM won't go over 2500) P0300 would be greatly appreciated.

A little more info - before P0300 etc... gas milage had suffered, I was having a mis or drop of idle at stops for a about a week or two. Even stalled once or twice. Other times it would drive fine with lots of power. I was thinking that was the throttle body. But now that there is a new one. I'm wondering if my catalytic converter has been slowly dying.
 

Mooseman

Moderator
P0125 Low coolant temp. Likely your thermostat needs replacing. Also cause for poor mileage and clogged cat (if it is clogged)

P0196 Low oil temp: Could also be related to thermostat

P0234 Turbo overboost. Another typo?

P0357 Ignition Coil G Primary/Secondary Circuit Malfunction

P0443 Evaporative Emission Control System Purge Control Valve Circuit

P0736 Reverse Incorrect Gear Ratio (???)

P1143 - HO2S Bank 1 Sensor 3 Lean System or Low Voltage

U0001 High Speed CAN Communication Bus (sometimes shows up when engine not running, generic)

U0101 Lost Communication with Transmission Control Module (TCM)

U0106 Lost Communication with Glow Plug Control Module (GPCM) (typo? This is for diesels)


 
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mgbspeedy

Member
P0125 Low coolant temp. Likely your thermostat needs replacing. Also cause for poor mileage and clogged cat (if it is clogged)

P0196 Low oil temp: Could also be related to thermostat

P0234 Turbo overboost. Another typo?

P0357 Ignition Coil G Primary/Secondary Circuit Malfunction

P0443 Evaporative Emission Control System Purge Control Valve Circuit

P0736 Reverse Incorrect Gear Ratio (???)

P1143 - HO2S Bank 1 Sensor 3 Lean System or Low Voltage

U0001 High Speed CAN Communication Bus (sometimes shows up when engine not running, generic)

U0101 Lost Communication with Transmission Control Module (TCM)

U0106 Lost Communication with Glow Plug Control Module (GPCM) (typo? This is for diesels)
Thanks. All of that went away with replacing of ignition switch and fully charged battery (after testing - all cells good), Back to original P0300.
 
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mgbspeedy

Member
Update
Weather finally gave me a little break.
I did compression test - All 6 cylinders between 195-205. Not bad for a 150K miles. (that's a relief)

Took off all coils and tested ohms with meter on 20k scale

One tested different than the rest. It was the new one that I replaced about 6 months ago when I threw a P0302. Replacing that coil did fix the problem at the time. Car ran like new afterwards.
(For the purpose of the data below - I will call this newer coil - coil X)

From casing to pins:
Pin 1 - All read 0 ohms.
Pin 2 - All read near 12 except coil X - 10.87
Pin 3 - All read between 9.45 and 9.79 except coil X - 19.05

A:smile: Could all 5 coils, which look to possibly be original, be failing or partially failing at the same time?
I really don't want to drop $400 plus on parts that I may not need.

B:} What is the likelihood that this difference could be an issue?

Also I have no way of testing fuel injectors, without a Pro scan tool, although main pressure was good at filter. Any tricks on how to do that for a DIYer?

@Mooseman - I tried to get my bluetooth OBD2 reader to work on iPhone with torque app. No luck in connection. May need to buy a different bluetooth. It appears that IOS is bluetooth 4.0.
 

Mooseman

Moderator
Bluetooth will not work with iPhones. It has to be a wifi type. Or if you can find an Android device to use with the bluetooth adapter.

The replacement coil, was is an ACDelco, Delphi or another aftermarket brand? It may have gone bad already with such a difference with the others.
 
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mgbspeedy

Member
Bluetooth will not work with iPhones. It has to be a wifi type. Or if you can find an Android device to use with the bluetooth adapter.

The replacement coil, was is an ACDelco, Delphi or another aftermarket brand? It may have gone bad already with such a difference with the others.
New coil is AC Delco.
 

christo829

Well-Known Member
I had a brand new Delphi branded coil go bad 6 months after I replaced a dead coil with it.

Can't find the list of resistance readings I took on the good coils I had and the bad one. If I
remember what clever thing I did with it, I'll post it up, or else I'll see if I can find the acceptable ranges in the shop manuals once I pull them out of storage.

So, don't rule out the new one being the failed part.

Good Luck!

Chris
 
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mgbspeedy

Member
I had a brand new Delphi branded coil go bad 6 months after I replaced a dead coil with it.

Can't find the list of resistance readings I took on the good coils I had and the bad one. If I
remember what clever thing I did with it, I'll post it up, or else I'll see if I can find the acceptable ranges in the shop manuals once I pull them out of storage.

So, don't rule out the new one being the failed part.

Good Luck!

Chris
Thanks. That would be great.

I've been reading up with all of the similar issues to mine. I've heard people say that replacing with new boots could solve misfire issue. I'm thinking of buying all new coil boots and gaskets. The boots are still pliable and don't look visibly bad. But some of the gaskets are definitely old and dry. Also have heard if the coils aren't seated exactly perfectly, it can give a random misfire too. The new coil definitely feels like it pops on the the spark plug better than the old ones. Don't feel much of anything when I put the old ones on.
 

KEEBZ489

Well-Known Member
check you intake manifold ,its known to leak apparently, I am going through the same thing you are right now , had P0302 , changed plugs , now P0300 , changed all 6 coils with aftermarket , $70 on amazon. only 3 out of the 6 pulled were Delphi , so someone had an issue along the way before me. truck runs very smooth now.
 
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mgbspeedy

Member
Update -
Finally broke down and took it to someone with a better diagnostic computer. They found #5 coil bad (Not sure how bad - all of them had same resistance checks). May just replace them all new. Also, MAP sensor bad, (easy fix) and said my "new" throttle body was bad (not sure I buy that). Will find out when I try replacing that again. My trust in mechanics being good diagnosticians isn't' very high. I'll report back with results.
 
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mgbspeedy

Member
Update -
So I replaced all 6 coils. Another new throttle body (Limited lifetime warranty - so free exchange), and the MAP sensor. Took me all of a half hour to swap these parts out. It was running a little better, but still had misfires. Got a P0306, so swapped the new coil for the 6 month old one. Back to P0300. Took it back to the Shop across the street. They said the plugs were fouled. These were brand new iridium plugs. I let them replace them, because I felt bad that I did all the work and they weren't getting money. (threw them a bone). I guess through all the other issues the misfiring, during testing, had fouled the plugs. I just put them in when the misfire problem started, so they only had less than a mile on them. Just a bunch of running during testing. (That's a new one on me). Anyway. with all of those changes it appears to be running better. But now I have a P0014 code. Wondering if this is just a quick swap out of the CAM sensor. (5 minute job) Or is there something else that could be causing that. This is the first time I'm seeing this code. Or could this be a result of the new throttle body? I've heard replacing with new could throw a few random codes for a while during the first so many miles while it is adjusting. I did do a relearn procedure however. I'm going to replace this part, as it is cheap and easy to replace, but I fear it is no coincidence that this code is being thrown after all these parts have been replaced. Any thoughts?
 

KEEBZ489

Well-Known Member
I went back to misfiring after work yesterday , I had low fuel , I had no time to stop before work , I put 1/4 tank in on the way home and still missing , I remote started the truck this morning and came out to the MIL on...… P0300 again

I have a fluke t5 tester that measure ohms , what should I be looking for on the coils ?
 
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mgbspeedy

Member
I went back to misfiring after work yesterday , I had low fuel , I had no time to stop before work , I put 1/4 tank in on the way home and still missing , I remote started the truck this morning and came out to the MIL on...… P0300 again

I have a fluke t5 tester that measure ohms , what should I be looking for on the coils ?
I don't recall the exact measurements of resistance I got. They are above in this this thread. However, all of mine were over 100K old so they recommend replacing them even if they look like they are testing good. I got mine from 1Aauto


Happy with new parts. In my case, what I was told is that if you are misfiring for a while, it could foul the plugs, and then that can actually cause the misfire.
 

Chickenhawk

Well-Known Member
Silly question, but what plugs did you use? Just double-checking, because you never said the brand of the iridium plugs. Our platforms ONLY like AC Delco 41-103 plugs.
 

Mooseman

Moderator
P0014 is typically the CPAS. You could pull the cam sensor and clean it to try first but it rarely fixes it.
 
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mgbspeedy

Member
P0014 is typically the CPAS. You could pull the cam sensor and clean it to try first but it rarely fixes it.
Thanks. I'll probably just do both. Cam position is an easy fix. The CPAS is tougher to get at so it's probably never been replaced.
 

Dreccomel

Member
Just joined the forum today after watching a few of MAY03LT's youtube videos. 2004 trailblazer 4.2. was driving and lost power. (unable to go above 2500 rpm) engine light started blinking. pulled over, and towed home. Initial code was p0300. In the past, Ive had p0302 etc did some tests, replaced coil. Problem solved. This time. Similar tests came up blank. Searched for vacuum leaks. tested fuel pressure. Tested throttle body. Found throttle body motor was bad. (there had been chattering at 2500 for a long time, so I wasn't surprised) Replaced. Watched videos on the subject. I had pulled the number 10 and 28 fuses while doing the work. Not much difference. Still throwing p0300. Found another video stating similar issues and a quick check.
The video is rough watch even though it is informative. (Summary-the fuse box mounts were loose) I did have one loose. The bolt housing was loose, but the bolt was difficult to turn. (tight when it shouldn't be) I did turn it in. (everything snug) Started engine and all kinds of new codes were thrown. Here's the list - P0215, P019, P0234, P0357, P0443, P0736, P1143, U0001, U0101, U0106 And then started acting like a bad battery. Even reset my clock. When I'd turn the key to ignition position but not start, the interior lights would dim. Loosening the bolt, helped with the lights dimming, but not the codes and battery appearing dead and starting issues. I'm worse off than I was before. Could a short be the problem (p0300) all along? Any help is greatly appreciated.
P0300 it means that there is more than one cylinder at fault. The following are the conditions for running the DTC (Diagnostic Trouble Code).

DTC P0013, P0014, P0105, P0107, P0108, P0122, P0123, P0125, P0128, P0217, P0218, P0336, P0340, P0341, P0365, P0366, P0502, P0503, P1114, P1115, P1120, P1221, P1336, P1345 are not set.
  • The engine is running.
  • The ignition voltage is between 10 – 18 volts.
  • The engine coolant temperature (ETC) is between -7 and +130⁰ C (19 - 266⁰ F).
  • The throttle angle is steady.
  • The A/C compressor clutch is not changing state.
  • The exhaust gas recirculation (EGR) flow test is inactive.
  • The fuel level is above 10 % percent.
  • The fuel cut-off or deceleration fuel cut-off (DFCO) mode is not active.
  • The PCM is not receiving a rough road signal.
Conditions for Setting the DTC
The PCM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed mandated standards.

Go here to get the service manual for your Trailblazer:

I also found this video, which is very informational and even though it is not on an envoy, the principle works the same for all vehicles from 2004.

I have also attached the GM procedure for the code P0300

I hope it helps...
 

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Dreccomel

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