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I have a 2003 Trailblazer 4.2L that will crank but will not start. It will turn over all day long, but it seems like it isn't getting fire.
I ran diagnostics on it and it threw a couple of codes: P1515,P1516, AND P0107. The first two have to do with the throttle body and the last one has to do with the Map sensor supplying too few votes to the ECM.
I replaced the throttle body with a brand new AC Delco one and it stopped showing P1515 and P1516. I tested the map sensor and it appears to be fine. My test was as follows:
Using a multimeter on DC Volts, I tested the gray wire and it showed 5 volts (black lead was grounded to negative battery terminal). Next, I tested the ground by touching the red lead to the positive battery cable and the black lead to the orange/black ground on the map sensor and the multimeter read 12 volts. Finally, I tested the voltage on vacuum and the voltage dropped as vacuum was applied.

If the MAP sensor is good, why am I still getting the error code and the engine still isn't starting?

All of that being said, when it turns over, it really seems more like it isn't getting fire/spark, but I'm not getting any codes for coils. I tested the coils just to be safe and they're all working as they should be. Plugs appear to be fine, as well...

I thought perhaps it could be the ignition control module, but, from what I understand, that's built into the coils on these vehicles.

Overlook my terminology. I'm anything but a mechanic and could use all of the help y'all could give me to help me figure out what the heck is going on.

Oh, and, for the record, the fuel pump is running, new fuel filter, fuel pressure gauge read 50 when testing, I tested fuel pump relay and ecm relays/fuses and they all appear to be fine, too.

Could it be that I need a new ECM?
 

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I have a 2003 Trailblazer 4.2L that will crank but will not start. It will turn over all day long, but it seems like it isn't getting fire.
I ran diagnostics on it and it threw a couple of codes: P1515,P1516, AND P0107. The first two have to do with the throttle body and the last one has to do with the Map sensor supplying too few votes to the ECM.
I replaced the throttle body with a brand new AC Delco one and it stopped showing P1515 and P1516. I tested the map sensor and it appears to be fine. My test was as follows:
Using a multimeter on DC Volts, I tested the gray wire and it showed 5 volts (black lead was grounded to negative battery terminal). Next, I tested the ground by touching the red lead to the positive battery cable and the black lead to the orange/black ground on the map sensor and the multimeter read 12 volts. Finally, I tested the voltage on vacuum and the voltage dropped as vacuum was applied.

If the MAP sensor is good, why am I still getting the error code and the engine still isn't starting?

All of that being said, when it turns over, it really seems more like it isn't getting fire/spark, but I'm not getting any codes for coils. I tested the coils just to be safe and they're all working as they should be. Plugs appear to be fine, as well...

I thought perhaps it could be the ignition control module, but, from what I understand, that's built into the coils on these vehicles.

Overlook my terminology. I'm anything but a mechanic and could use all of the help y'all could give me to help me figure out what the heck is going on.

Oh, and, for the record, the fuel pump is running, new fuel filter, fuel pressure gauge read 50 when testing, I tested fuel pump relay and ecm relays/fuses and they all appear to be fine, too.

Could it be that I need a new ECM?
I have a 2003 Trailblazer 4.2L that will crank but will not start. It will turn over all day long, but it seems like it isn't getting fire.
I ran diagnostics on it and it threw a couple of codes: P1515,P1516, AND P0107. The first two have to do with the throttle body and the last one has to do with the Map sensor supplying too few votes to the ECM.
I replaced the throttle body with a brand new AC Delco one and it stopped showing P1515 and P1516. I tested the map sensor and it appears to be fine. My test was as follows:
Using a multimeter on DC Volts, I tested the gray wire and it showed 5 volts (black lead was grounded to negative battery terminal). Next, I tested the ground by touching the red lead to the positive battery cable and the black lead to the orange/black ground on the map sensor and the multimeter read 12 volts. Finally, I tested the voltage on vacuum and the voltage dropped as vacuum was applied.

If the MAP sensor is good, why am I still getting the error code and the engine still isn't starting?

All of that being said, when it turns over, it really seems more like it isn't getting fire/spark, but I'm not getting any codes for coils. I tested the coils just to be safe and they're all working as they should be. Plugs appear to be fine, as well...

I thought perhaps it could be the ignition control module, but, from what I understand, that's built into the coils on these vehicles.

Overlook my terminology. I'm anything but a mechanic and could use all of the help y'all could give me to help me figure out what the heck is going on.

Oh, and, for the record, the fuel pump is running, new fuel filter, fuel pressure gauge read 50 when testing, I tested fuel pump relay and ecm relays/fuses and they all appear to be fine, too.

Could it be that I need a new ECM?
A little background. This vehicle was my daily driver up until about 2 years ago. It started idling rough and acting like it wanted to die at times, but I could tap the throttle and it would be fine. I parked it one day and didn't start it for about a month. When I finally did start it, it was running really rough....bad enough that I felt it was best to just cut it off. Once I turned it off, it never started back since. Like I said, it will turn over all day long (at least, until the battery goes dead) but it just won't start.

New battery, as well, if that matters.
 

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With a crank-no-start I often resort to a quick (no more than 2 seconds) spray of starter fluid to the air filter then crank and see if it at least sputters. That would prove at least some spark and maybe a lack of fuel. Have you examined the fuel injector wiring harness? I have seen a couple of owners have some issues with degraded wiring at the connector near the rear of the engine under the resonator.
 

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Discussion Starter #4
With a crank-no-start I often resort to a quick (no more than 2 seconds) spray of starter fluid to the air filter then crank and see if it at least sputters. That would prove at least some spark and maybe a lack of fuel. Have you examined the fuel injector wiring harness? I have seen a couple of owners have some issues with degraded wiring at the connector near the rear of the engine under the resonator.
thanks for replying....I tried starter fluid and it still won't hit. That's part of what has me convinced that it isn't getting spark/fire.
I haven't checked that harness, but I certainly will, now.
I have a new map sensor coming Monday, just in case... Was 80 bucks at the local auto parts store so I ordered from Amazon.
I'll check that harness tomorrow. Sounds like that could be the culprit. Just have to find it lol
Throws me off that I'm not getting any codes for ignition system, though
 

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Well if it didn't fire with a shot of starter fluid then it very well may be as you suspected, a spark issue and not the injectors.
 

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What are you using for a code scanner and does it show code status, like 'current' or 'pending' or 'history'?
 

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I think it would still start with a bad MAP sensor but likely in a limp mode of sorts, running off of preprogrammed instructions. I am NOT certain of this though
 

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OK, now I AM certain. I just went out and disconnected the MAP sensor on my 2002 and it started right up fine.
 

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Discussion Starter #9
What are you using for a code scanner and does it show code status, like 'current' or 'pending' or 'history'?
What are you using for a code scanner and does it show code status, like 'current' or 'pending' or 'history'?
I'm using a RealWorks OBD II & CAN Scan tool I picked up at Rural King for 80 bucks.
It shows active, pending, and stored, allows me to clear codes, view live data, etc
 

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OK, now I AM certain. I just went out and disconnected the MAP sensor on my 2002 and it started right up fine.
I've heard of "limp mode", but I really ain't familiar with it. I'm assuming that's what the vehicle was in last time it started because it was idling horribly and would barely move. That's why I felt the need to cut it off....hasn't started back since.

I'm very confused on having a solid gut feeling that it just isn't getting fire, while also getting a code about the map sensor. I've read a lot of forums on here and other places, watched a few youtube videos, and still haven't really found an exact answer to my problem. I wondered if it could be the ECM. As I understand it (and, please,correct me if I'm wrong) the MAP sensor sends voltage back to the ECM and that basically determines how much fuel/etc to start the engine...As i tested the MAP sensor, it had good voltage and good ground and if yours will start with the map sensor removed, then I don't see why mine wouldn't start, too....

I feel like my issue is electrical...

Some information I forgot to mention before:
The last time I started the vehicle, my dash was fine as far as lighting and gauges working correctly, but I noticed the lights on my radio were flickering. Not sure that that matters in the grand scheme of things, but it has since stopped. I chocked it up to the fact that I had a really shotty battery on it at the time. Since I replaced the battery, it hasn't done that and everything seems to be fine with the vehicle, other than the fact that it will turn over and just won't start.

I think tomorrow I will check that harness and then I may start pulling coils out and checking the gap in the plugs...I did that a few months back and it'll probably be pointless, but I'm at a loss for anything else to try.
 

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Has the security light ever come on aside from the 2 seconds or so at first key on? There are conditions under which the security system will disable fuel delivery if it believes a theft is occuring but the security light would come on then I think.
 

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Has the security light ever come on aside from the 2 seconds or so at first key on? There are conditions under which the security system will disable fuel delivery if it believes a theft is occuring but the security light would come on then I think.
Yeah, actually, it did...not for long, but for longer than those 2 seconds. I can't remember why. I believe it may have been when I was fiddling with the battery and then went to start it and it was on....Heck, yesterday it and the service 4wd light came on together for about 15-20 seconds before they finally went off.

How would i bypass that, if that's the case?
 

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Not easily done... bypassing security. And security would not explain any of the rough idling you had when this began either.

Since the security light did go out that suggests the fiddling around with the battery connections and such caused a temporary security issue. The security light would remain on if it were preventing startup.
 

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Earlier you said you tested the coils. How did you test them? Have you confirmed power to them with key on?
 

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Earlier you said you tested the coils. How did you test them? Have you confirmed power to them with key on?
I would have liked to have pulled them out and used a spark tester, but I don't have one. Instead, I checked to make sure they were getting power at the connectors. I'll probably pull them tomorrow and fully check each one individually.
Wouldn't I have a coil code if that were the case?
 

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I don't think there is a 'coil code'. You might be thinking of a misfire code but that requires the engine to be running to be set for either a unspecified misfire or a cylinder specific misfire.
 

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Discussion Starter #17
if I have a bad coil, I have 6 bad coils lol......I'm getting no codes for coils/ignition system, but that doesn't mean I'm ruling them out. But when it's turning over, it's not doing anything at all...You know how you can usually kinda hear it sparking in a couple cylinders as it starts...almost like you're listening for a miss? Hoping you know what I'm talking about...anyways, you cant hear it at all...it's like it's missing on all 6 cylinders.

Could it be timing? Would the crankshaft sensor control that?
 

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I don't think there is a 'coil code'. You might be thinking of a misfire code but that requires the engine to be running to be set for either a unspecified misfire or a cylinder specific misfire.
You're probably right...I remember getting a code when I had a bad coil pack before and had to replace it. That was years before this issue, though, so I wouldn't think they're related. It probably was a misfire code...

Looks like I'm pulling 6 coils and testing them tomorrow...
 

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You're probably right...I remember getting a code when I had a bad coil pack before and had to replace it. That was years before this issue, though, so I wouldn't think they're related. It probably was a misfire code...

Looks like I'm pulling 6 coils and testing them tomorrow...
Would it not throw misfire codes if I had it hooked up while trying to start it?
 

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No it wouldn't set misfore codes during a startup or attempted startup.

I would look closely at things that all the couls have in common, they all get their power from the same source and they all get the ground from the same place. Power comes in the pink wires to terminal A from PCM 1 fuse 28. And the ground is on terminal C, the black wires and they all connect to G109 on the lower side of the engine. I will see if I have a graphic of that ground point.
 
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