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post #1 of 12 (permalink) Old 12-28-2017, 02:26 PM Thread Starter
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No Start, OBDII Fail to Communicate

'08 Cobalt Manual Trans: NO START, OBDII FAIL TO COMMUNICATE.
When I say "No Start", I mean it doesn't even turn over, nothing happens.
I've read enough forum pages to feel like this is NOT completely covered. First, OBDII works, I've gotten codes on this car with this device a month ago, but not any longer, connected it to my Suburban today to verify because that seems to be the number one response. Second PCM (ECM) is bad, seriously doubt that, I just bought it and it was already flashed from gmflash.com. Third, battery is strong, connected jumpers to my Suburban (with Suburban on) just to be sure.
Recent driving history, going down the road it would randomly start shuddering or feeling like it was firing on only two cylinders, so shift to neutral shut off and restart, problem temporarily solved. Eventually the tach started shutting off, and then instead of shuddering the motor would just shut off, same remedy, neutral & restart. One day it wouldn't start in the morning. I scanned it, and it indicated the evap canister, which was replaced by the dealership last year, and (thanks to forums) shouldn't cause a no start. Because it was a gradual decline in performance and didn't fail to start "just out of nowhere", I bought an already flashed PCM (ECM), my Suburban (last month) was doing similar things including the no start but not the OBDII- "Fail to Communicate", everyone and every forum said it's not the computer, guess what- it was. Dropped it in and it fired right up.
What I've done: checked EVERY fuse inside and out, continuity from PCM housing to chassis, start relay bypass (turns over-still no start), clutch switch bypass (did nothing), checked chassis grounds, ignition cylinder was replaced due to recall, anti theft works and turns off with the key. Also before the no start I switched the #1 coil pack with the #4 coil pack because I read on a forum that the #1 might be going bad and that's the one the computer reads, but that did nothing to improve things and eventually I suffered the no start.
HELP!

Last edited by Mike Hunt; 12-28-2017 at 02:49 PM.
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post #2 of 12 (permalink) Old 12-28-2017, 02:42 PM
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So let me clarify a little. You've pretty much tested most things for a no-start, because that is the issue you are having. It won't start. Crank but that's all she wrote, and won't actually fire up. Or does it fire up and die immediately? When it did run, were there any codes or a CEL? Honestly what it sounds by reading the post is a ground issue, and there is a ground that is deteriorating, and it doesn't have to be a chasis ground. It could be the ECM ground, or a ground from the ECM (as most have multiple grounds). Bad/no grounds have very weird results. If you turn the key on and your gauges don't cycle, or you don't get a CEL for 10-20 seconds, then your ECM isn't turning on, and you would need to check power and ground at the ECM. That would be the only reason besides a bad data cable (one from OBDII port to ECM). Time to pull out the Multi-meter and start checking actual pins for continuity, voltage and ground. It sounds like wiring to me, not a ECM or any sensors. If you get the ECM to communicate and it still doesn't start, start looking for codes or action from the CPS or CamPS's. Give us some updates and we will definitely be able to help a lot more.

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post #3 of 12 (permalink) Old 12-28-2017, 03:52 PM Thread Starter
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Much Thanks!
I didn't see your response before I edited so some of this may be redundant, to clarify a little more, when I say no start, I mean does nothing unless I try to crank with my relay bypass switch. Yes the gauges cycle and all the lights go off except the seat belt. There is power to the cig ltr, and the radio works I do have continuity from the ecm housing to the chassis. It has sat for a month or so and the only code I remember indicated was the fuel evap canister, only after it sat is when I got the fail to communicate, I had to fix the suburban first, it took me a while to get back into it.

I will continue testing for voltage and grounds in the fuse panels.
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post #4 of 12 (permalink) Old 01-04-2018, 10:51 AM Thread Starter
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Still no luck. with key on I do have power to what seems to be most important (and the fuses are good), IP IGN, PCM/ECM, BCM2, BCM3, EPS, DLC, CRANK, ECM/TRANS, INJ. BUT NO POWER on CHMSL, DRL or FUEL PUMP. I may have mentioned before I can inject power to the fuel pump fuse and it comes on, is the DRL circuit associated with the fuel pump? The DRL fuse is right up against the fuel pump relay opposite the fuel pump fuse. Where does it come from?

To be certain the relays are installed correctly if I have pwr on one pin and my choices on the relay are 87 or 30 then 87 should go to the power, correct?

Last edited by Mike Hunt; 01-04-2018 at 11:11 AM.
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post #5 of 12 (permalink) Old 01-04-2018, 11:46 AM
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Did you check the big fuse in the trunk? It sounds to me that your missing one of the 3 BCM B+

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post #6 of 12 (permalink) Old 01-08-2018, 04:17 PM Thread Starter
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YES, I checked the fuse in the trunk, it's good and no corrosion, this is a FL car so there's hardly any "corrosion" or rust anywhere.
I found a thread on this site, user's Charlie Gates and 1966tbird from last July, "2008 Cobalt LS No Crank" but it leaves me flat. It deals with an engine swap but still has some good info:

Below is an excerpt and following it I list my differences.

"Old 07-24-2017, 04:42 PM
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Sorry Charlie
The connectors are in the correct position. The second image of the BCM is just rotated.
If you rotate the image it will look just like whats in your car. This Ipad didnt allow me to rotate the image.
Remember the signal OUT of the BCM will be +5V. In the on position will be -+5V and the pin 56 will have 1.5V to 2.5V in start position with the connector connected to the BCM

Notice from the schematic pin 62 is the +5V reference to the ignition switch. This goes throuh the switch back to the BCM on pin 56.
Note the wire colors, you should find them at the ignition switch at the column....yes?

Use your multi-meter to check the voltage while every thing is plugged in.

With the C2 connector disconnected from the BCM you can check the resistance & continuity through the ignition switch and see if it is there and working.

With the connector C2 connected to the BCM you can check to see if you have voltage on both pins and thier value.
Pin 62 should be +5V all the time......with good battery & good fuses.
Pin 56 will be Zero when off. ~+5v in run possition and ~1.5-2.5V with the ignition switch in the start position.

If your tester light is not working, it may not work for 5V. Use your DVM.
Like
BC
Last edited by 1966tbird; 07-24-2017 at 04:57 PM."

*These are my the differences
On BCM2 (connected)
On pin 62 I got with key OFF- 5V, RUN- 4.019V, START- 4.267
On pin 56 I got with key OFF- 0V, RUN- 4V, START- 2.978

I am left flat because Charlie got nothing on pin 56 but I did, he bought 2 "ECMs" and figured it out.
I did the following ignition ohm test and it checked out.

"Old 07-24-2017, 06:08 PM
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Quote:
Originally Posted by Charlie Gates View Post
.... Probing the wire with a DVMM will be safe correct? ....
Brain surgery is safe.....if you know what your doing!

WITH THE BATTERY DISCONNECTED
have the battery disconnected, then disconnect BCM C2. Turn the ignition switch to on and measure the resistance between C2-56 and C2-61 on the CONNECTOR with the connector disconnected from the BCM.

If the switch is working, you will see continuity between C2-56 and C2-61 with the ignition switch in the on possition and a few K ohms in the start position, and open circuit with the key out.
Remember,
This is testing the ignition switch."

*NOTE: there are NO wires on BCM2 pins 60,61,63 or 64, so the above test was performed on pin 62.

The above test checks out.

What can we do next?

---------- Post added at 04:17 PM ---------- Previous post was at 02:43 PM ----------

Coby7, do you have an '08 2.2L PCM pinout list for the connectors?

Last edited by Mike Hunt; 01-08-2018 at 03:51 PM.
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post #7 of 12 (permalink) Old 01-09-2018, 04:45 AM
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In the 07 the PCM becomes and ECM because it integrates the Ignition module. The older models would have had a seperate ignition module on top of the valve cover.




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post #8 of 12 (permalink) Old 01-09-2018, 08:47 AM Thread Starter
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Thanks Coby7
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post #9 of 12 (permalink) Old 01-09-2018, 09:12 AM
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I see you watched Mr GoodBurger ''Any buddy seen Mike Hunt?''

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post #10 of 12 (permalink) Old 01-10-2018, 11:57 AM Thread Starter
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What is the relationship with the HVAC relay on the BCM with crank run? I hear a clicking from the BCM when trying to crank, discovered it was the HVAC relay, any chance this could be my problem? I discovered this a while back but I was like no way HVAC would cause a no crank, but now I'm forced to ask.

Last edited by Mike Hunt; 01-10-2018 at 03:06 PM.
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