Question about 2003 Pontiac Vibe

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Trying to work on my friend's 2003 Pontiac Vibe after she had a complete engine failure. We replaced the engine with a salvage & had it running fine when it was up on jacks. After it was let down, however, it ran for a few seconds, died & refused to even turn over. We found & replaced a blown AM2 fuse & found the wires to the Cylinder 3 fuel injector were pinched & shorting out on the engine block. Clipped & rejoined the affected wires but now, we have a check engine light & it is giving a code for #3 cylinder misfire... We checked power to the spark plug & coil pack - all fine, the fuel injector plug has voltage but the #3 injector is still not squirting fuel. With the fuel rail out, we swapped the injector plugs over & the problem follows the #3 plug. Could the #3 cylinder injector wire getting pinched & shorting out on the engine block have turned something off in the computer, maybe as a safety?? And if it has, how do we turn that cylinder back on? Thanks & I hope someone out there can understand at least some of my ramblings... LOL

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  • Expert
  • 693 Answers

Where i would start with the injectors shorting out may have shorted out your ecm " computer" This will cause Everything you listed. You can reset just need to contact dealer and find out you reset on this kind of vechical.But i would guess it's fryed with all the short's , Best of luck to you. I i can help any futher just ask, I'll do my best.

Posted on Apr 09, 2011

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  • Pontiac Master
  • 8,270 Answers

Hi, I understand you just fine, and you've done a great job of troubleshooting this problem. I assume the engine is now turning over since you replaced the AM2 fuse, right? Unfortunately, you may have burned a component in the computer by shorting the injector wires. If you look at the diagram for that fuse, you can see that the PCM was powered by it and it is likely a lot of current went thru there. The PCM is behind the glove box. I would recommend opening the computer to see if it can be fixed. You want to trace the conductor from connector C, pin 3 (the white wire) to see if there is anything obviously burned up. Replace any burned components and reconnect the PCM. Please let me know if you have any questions, and thanks for using FixYa.

Trying to work on my - jturcotte_1508.gif

Posted on Apr 09, 2011

  • 20 more comments 
  • Koonses Apr 09, 2011

    Well, we fixed a plasma TV with what turned out to be a blown capacitor on the main power supply board last month, so this should be a piece of cake, right? Hahaha

    Hubby is working on getting at the PCM now... Will let you know what we find.

    Thanks for all your help!

  • Jeff Turcotte
    Jeff Turcotte Apr 09, 2011

    Sounds like you're a pretty darn handy team. I have to go to bed now, but will check messages in the morning.

  • Koonses Apr 09, 2011

    OK... checked out the PCM (we assume it IS the component behind the glove box, with 4 large-ish multi-pin plugs going into it) & nothing appears to be burned - it doesn't smell burned, there is nothing that's brown or black or seeping, nothing looks like it blew (like the blown capacitor we found on our TV) - it looks all shiny & in perfect shape. In the wiring diagram on the right, that you posted, the fuel injector 3 control APPEARS to be separate from the PCM. Is it? And could that be the problem? And if so, where would we find it? And do you have any other ideas? THANKS!!! And yes, we are pretty handy! LOL

  • Koonses Apr 09, 2011

    Is the PCM & the ECM the same thing??? The board we found says "Engine Control" on the box...

  • Jeff Turcotte
    Jeff Turcotte Apr 09, 2011

    They are the same thing. Let's try this. Did you find the "C" connector that has the injector pins on it? Were you able to find that particular pin 3? What I woud do is to check the impedance on that pin to a ground pin of the module and compare it to the impedance of the other 3 injector pins (1, 2, and 4). This will tell us if it's the PCM or something else. I will look at the diagrams again to see if I can give you more hints, like which pin is ground!

  • Jeff Turcotte
    Jeff Turcotte Apr 09, 2011

    OK, there are 4 connectors on the PCM. Connector C1 has 34 pins. C2 has 35 pins, C3 also has 35 pins, and C4 has 31 pins. So C1, the connector that has the injector wires, is the only one that has 34 pins in the PCM. The injector firing pins are 1, 2, 3, and 4 on that connector, and the wire colors are yellow, black, white, and blue, respectively. The ground wires are on pins 6 and 7, and their wire colors are both white with a black stripe. So find those pins and hold your ohmmeter to pins 1 and 6, then 2 and 6, then 3 and 6, and finally 4 and 6. How to the ohms compare? If pin 3 is lower or higher, trace the pin again inside the PCM to see what the problem is. Would really like to avoid getting a new PCM, as this can bring other problems.

  • Koonses Apr 09, 2011

    We did like you said & checked the ohms on the 4 injector firing pins in the PCM... Pin 3 & 6 had 110.6 ohms, compared to 113.7 / 113.8 on all the other 3. Does that suggest that there is a problem with the PCM board? And what other problems could replacing it cause?

  • Jeff Turcotte
    Jeff Turcotte Apr 09, 2011

    Good work. That's not a very convincing result, but it is what it is. The problem is probably quite small but large enough to prevent the injector pulse. There is a tiny relay that switches the pin 3 to ground to create the pulse, but I don't have a schematic of the PCM internals. I was hoping the relay would be shorted, but it isn't. More likely, it has failed open, and without a schematic I cannot tell you how to check for that with the PCM out of the car. Another more conclusive test you can run is to put it all back together and check the AC voltages during cranking. To do that, you have to probe the back of the connector far enough to touch the wire or terminal from behind. Find a power pin, such as pin 9 on the C4 connector. The wire color there is black with an orange stripe. Set your meter to ac volts and check C1, pin 1 verses C4, pin 9 while cranking the engine. Similarly for the other injector pins. Sorry to put you thru all these steps, but we do want to make sure this thing is bad. In the next comment I will give you the details on replacing the PCM.

  • Jeff Turcotte
    Jeff Turcotte Apr 09, 2011

    A new pre-flashed computer is $335 at autozone. I would shop around for a better deal, but autozone is my source for information and pricing. When replacing a PCM, even after the module is flashed with the appropriate logic for your car, it has to learn the parameters of the particular sensors on your car before it will run well. You will also have to reprogram your keys, assuming there is a passlock anti-theft system in the car. Now, when the computer costs that much (many models are less expensive than yours), I always recommend trying to find a used one at a salvage yard. The problem then becomes finding one that is an exact match. If it is the right unit, but not an exact match to the year and model, it will have to be reflashed by the dealer. Even if it is an exact match, the key codes will have to be erased with a special scanner so that your keys can be programmed into the module.

    So this is why I prefer to repair the module, if at all possible. :o'

  • Koonses Apr 09, 2011

    Thanks SO much for all your help - you're a real life saver!! If we can figure out whether something on the PCM is bad & exactly what it is, we are up for the repair, if possible. We found one on ebay that appears to be a match but he doesn't say if it works & doesn't accept returns, so... Also, I would prefer not to have to mess with the keys, if at all possible! LOL OK,,, off to do the AC voltage test... results soon!

  • Koonses Apr 09, 2011

    Slight hiccup... C4 pin 9 wire is blue with a white stripe, not black with an orange stripe :S

  • Jeff Turcotte
    Jeff Turcotte Apr 09, 2011

    Hmmm...not sure why but no big deal. You just need to find a hot wire somewhere. Is C2, pin 8 red? That one should also be hot with the ignition on.

  • Jeff Turcotte
    Jeff Turcotte Apr 09, 2011

    C4, pin 3 should be hot all the time. wire is red with a white stripe.

  • Jeff Turcotte
    Jeff Turcotte Apr 09, 2011

    Maybe a bit of good news. Checked on anti-theft and it looks like GM decided to spare the Vibe from their ridiculous passlock system. So maybe there is no issue with programming keys into the PCM.

  • Koonses Apr 09, 2011

    Well, that is good news :D Just tested the AC Voltages & found: With C4 pin 3 connected to... C1 Pin 1, it goes up to 39V while cranking & drops to approx 1.04 while running (but it does fluctuate so...); C1 Pin 2 goes to 18V while cranking & drops to approx 1.04; C1 Pin 3 (our problem child LOL) goes to 96V while cranking & drops to 0.05 while running...; And C1 Pin 4 goes to 18V while cranking & drops to 0.70V while running. Does that help?

  • Jeff Turcotte
    Jeff Turcotte Apr 09, 2011

    Definitley not getting a pulse to injector 3. I would not buy a computer on eBay without a guarantee from a highly-rated seller. Your local salvage yard is a better source, as they will generally give you another one if the first one doesn't work--and there's no shipping, etc. However, the odds of the computer working without a reflash are much lower without an exact match. So I would price both the used computer and the reflash together when comparing to buying a new reflashed module. You'll have to ask your dealer to price the reflash. It could be any GM dealer. But I would try the used computer before paying for a reflash, as you might get lucky with the logic.

  • Koonses Apr 11, 2011

    Well, the guy on ebay said he would take a return within 14 days if it didn't work out, his feedback is really good & he has free shipping. So Adam went ahead & bought it... He SAYS it came out of an 03 Vibe, which would be the same vehicle, sooo... fingers crossed! Thank you again for all your help - we really couldn't have done this without you! I'll let you know how the replacement PCM works out... :)

  • Jeff Turcotte
    Jeff Turcotte Apr 11, 2011

    Thanks for the note. I'm waiting with baited breath and hoping for the best!!!

  • Koonses Apr 16, 2011

    It finally arrived today! And Adam had it installed shortly thereafter LOL. All 4 cylinders are now working!! Now we're wondering how long the "new" ECM normally takes to learn the parameters of the engine. When he 1st tested it, the engine seemed to be running hot & the blower wasn't working at 1st. Then, suddenly, the blower kicked on but the temp gauge is still hovering in the mid-hot range. Is this kind of behaviour normal when the ECU is replaced & if so, how long does it normally take to figure it out?
    Thanks again!!

  • Jeff Turcotte
    Jeff Turcotte Apr 16, 2011

    Cool beans! That is not normal behavior, but perhaps the previous owner of the computer had the wrong temp sensor installed. Keep in mind that you have also just installed an engine. I'm assuming you moved all the sensors from the old engine to the new one--yes? Is the replacement engine new or used? It can take up to a few hundred miles for the computer to tweek every last parameter, but the car should be running OK after a good 20-mile drive. The gage may have a new norm after the change, but the car should not be getting too hot. If that continues, you may need an adjustment to the fan switch logic. Please get back to me if the engine is still getting too hot.

  • Koonses Apr 16, 2011

    He only had it out for about 4 miles yesterday... So he took it out again this morning for a bit longer & had it up to 55 for a good stretch & said after about 6 miles, the temp was holding steady in the cool-mid range. He checked it with the temp gun when he got back here & said it was reading 198 deg. He says he fairly sure its just the new computer learning & setting the parameters. The replacement engine is a used one & I believe the guys (hubby & his friend) just installed it with whatever sensors it came with, so we've probably got a mixture of sensors now LOL. Still, Adam said every time he runs it, it seems to be more stable. I'm just happy we're running on 4 cylinders again!
    Thanks again! I've said it before but we really couldn't have done this without your help!

  • Jeff Turcotte
    Jeff Turcotte Apr 16, 2011

    Sounds like you have it licked. Good job! Are you ready to become a FixYa expert? If not, help a few more friends and you'll be ready soon! Let me know if there is any further problem.

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