No spark, but fuses, plugs and coils are fine, code U2129-00?

Tiny
SHERLOCKTHC
  • MEMBER
  • 2007 CHEVROLET COBALT
  • 2.2L
  • 4 CYL
  • 2WD
  • MANUAL
  • 234,000 MILES
I was driving, then the engine shut off. It will crank but no spark. I couldn't jump start it, but I saw the rpms moving. I checked the fuses and tried a few tricks but no luck. After I had it towed, the tow driver left the lights on and drained the brand-new battery. I charged it but my bidirectional scanner only reads a U2129-00 code now. I've had a lot of work done lately to pass inspections. I was trying to fix a P0171 code the day this happened. It was running fine, I took off the throttle body to check for leaks. I put it back on, drove only 3 blocks away and it shut off. The scanner seems to communicate with everything just fine. Upon inspection I discovered oil had leaked down the wire bundle into the ECU plug and elsewhere. I cleaned it all up but still no luck. The car is mechanically sound, I just put a ton of money into it. I've done some random troubleshooting but need help from square one. I'm worried it's a bad wire somewhere but don't know how to check or where to start. Please help bring it back to life!
Thursday, March 23rd, 2023 AT 5:50 PM

22 Replies

Tiny
BORIS K
  • MECHANIC
  • 836 POSTS
Hello,

U2129 lost communication with RFA- remote function actuator.
This fault would not cause any non-starting situations.

Do you have communication with the ECM (Engine Control Module)?
If so, next check live data using your scan tool. As it is bi-directional it should be capable of displaying RPM signal. This signal is important for the spark and injectors to be switched by the ECM.

At the ignition coils check
Pin A, black wire ground
Pin D, pink/black wire 12V

You can check this by using a voltmeter or test light.

How to use voltmeter:
https://www.2carpros.com/articles/how-to-use-a-voltmeter

How to user test light:
https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

A good video how to test spark:
https://youtu.be/1zQQy9noYQ0

Hope this helps.

Cheers, Boris
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Friday, March 24th, 2023 AT 10:19 AM
Tiny
SHERLOCKTHC
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Thank you for your reply! I do have communication with the ECM. It is raining hard right now so I can't test anything yet. I'll reply as soon as I can test.
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Friday, March 24th, 2023 AT 4:47 PM
Tiny
SHERLOCKTHC
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I do not have power to the ignition coils. What should I check next?
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Saturday, March 25th, 2023 AT 9:53 AM
Tiny
BORIS K
  • MECHANIC
  • 836 POSTS
Hello,

As you have no power to ignition coils, pin D pink/black wire, I would suggest first checking INJ fuse45(10A) in the under-hood fuse block, next to left strut tower.
See image below.

This fuse supplies 12V to all 4 ignition coils and to all four fuel injectors on pin 1, pink wire.

A good link:
https://fuse-box.info/chevrolet/chevrolet-cobalt-2005-2010-fuses-and-relay

How to check a fuse:
https://www.2carpros.com/articles/how-to-check-a-car-fuse

Cheers, Boris
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Monday, March 27th, 2023 AT 12:55 AM
Tiny
SHERLOCKTHC
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That fuse is good. All fuses are good.
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Monday, March 27th, 2023 AT 4:29 AM
Tiny
BORIS K
  • MECHANIC
  • 836 POSTS
Hello,

Have you checked if the injectors are getting 12V on pin 1, pink wire?
If they are then this could point to a possible wiring issue between the fuse block and the ignition coils.

See image below of engine fuse block showing fuse INJ45.

How to test wiring:
https://www.2carpros.com/articles/how-to-check-wiring

Cheers, Boris
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Tuesday, March 28th, 2023 AT 9:18 AM
Tiny
SHERLOCKTHC
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I'm having trouble getting the connector off to check the pin. Any tips?
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Thursday, March 30th, 2023 AT 5:46 PM
Tiny
BORIS K
  • MECHANIC
  • 836 POSTS
Hello,

There is a light blue/grey clip-on top of the injector connector which needs to be levered up.
Then you will be able to remove the connector from the injector.

See image below.

Cheers, Boris
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Friday, March 31st, 2023 AT 7:07 AM
Tiny
SHERLOCKTHC
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How much voltage should the coils read? When I have the key in the on position, I have power to the coils but it's a low voltage. Yet when I crank, I don't get a spark. Any idea why?
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Thursday, April 13th, 2023 AT 5:53 PM
Tiny
BORIS K
  • MECHANIC
  • 836 POSTS
Hello,

You should measure battery voltage, 12V, at each ignition coil on pin D, pink/black wire.
This voltage should be the same as measured on each fuel injector on pin 1, pink wire.
Please ensure that you have a good ground when measuring the voltage.

Cheers, Boris
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Friday, April 14th, 2023 AT 6:55 AM
Tiny
SHERLOCKTHC
  • MEMBER
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My multimeter is reading 0.67v on pin D on the coil. Battery is reading 12v so that's fine. What could cause that difference?
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Friday, April 14th, 2023 AT 4:13 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

I noticed it has been a couple of days since we have been in contact. Have you been able to make any progress? We are interested in knowing.

Also, as Boris said, you should have battery voltage at the coils. If you are getting0.67v, either you have a broken wire, shorted wire, poor electrical connection at the power supply, or even a failing splice.

Let us know what we can do to help.

Take care,

Joe
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Sunday, April 16th, 2023 AT 6:45 PM
Tiny
SHERLOCKTHC
  • MEMBER
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Apologies, I couldn't do much work, my area was hit with storms. I found a melted wire resting on a coolant line. I don't believe its a power wire, but I will send pictures and make the repair ASAP. I still need to check voltage at the fuel injectors, I'm still having trouble removing the connectors.
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Monday, April 17th, 2023 AT 7:22 AM
Tiny
BORIS K
  • MECHANIC
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Hello,

It is important to check the voltage on the pink wire at an injector. This would confirm if the output side at the engine fuse block from fuse INJ45 is intact.
Also measure that you get battery voltage at this fuse.

Please send us that picture of the melted wire.

Cheers, Boris
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Monday, April 17th, 2023 AT 7:43 AM
Tiny
SHERLOCKTHC
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This is the burnt wire and the line it was resting on. I'm currently working on it.
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Monday, April 17th, 2023 AT 4:15 PM
Tiny
SHERLOCKTHC
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I repaired the wire but there was no improvement. When I unplug each coil, the voltage goes up. When I unplug 3 coils, the 4th coil reads 2.8v. Any idea what could cause this and where to start looking?
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Monday, April 17th, 2023 AT 6:41 PM
Tiny
SHERLOCKTHC
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Any thoughts on my last reply?
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Thursday, April 20th, 2023 AT 6:52 AM
Tiny
BORIS K
  • MECHANIC
  • 836 POSTS
Hello,

Have you managed to check the voltage at the injectors on pin 1, pink wire?
This would serve as a check for the 12v supply from fuse INJ45.
If the supply at the injectors is 12V it would mean that the output at the engine fuse block from fuse INJ45 is intact, and you are looking at a possible wiring issue to the coil pack on the pink/black wire.

Cheers, Boris
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Thursday, April 20th, 2023 AT 9:16 AM
Tiny
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I'll remove the fuel rail tonight to test the injectors. I still can't remove the connectors from the injectors, I can't figure out how.
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Friday, April 21st, 2023 AT 4:54 AM
Tiny
BORIS K
  • MECHANIC
  • 836 POSTS
Hello,

As previously shown, you will need to push up the light blue clip-on top of the injector connector. No need to remove the fuel rail.

See image at below.

Cheers, Boris
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Friday, April 21st, 2023 AT 7:01 AM

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