P1571 & C1277 codes, What next?

[dougelam]

I am getting these codes and they are current. My 2002 base convertible was running fine until those codes showed up. I confirmed power and grounds but I would like to check for an output to the pcm from the ebtcm. I cannot find what pin to monitor and when I do what is the correct voltage that I should see? Any help/thoughts would be greatly appreciated

 

[dadaroo]

I'll look into these codes and see what I can do to help. I should have all the info for 2002. I will want to email you the PDFs of everything. Just PM me with your email address. Will try to pull everything later today.

 

[dougelam]

I'll look into these codes and see what I can do to help. I should have all the info for 2002. I will want to email you the PDFs of everything. Just PM me with your email address. Will try to pull everything later today.

Thanks dadaroo

 

[dadaroo]

Four PDFs coming your way. I included my phone number so if you need anything just Post it here or call.


PS: Need to make sure the EBCM grounds e good as first step.

 

[Hib Halverson]

Once you confirm that power and grounds are in good condition and you've checked the wiring harness and all connections, you're going to need a scan tester which supports the ECM and the EBTCM. You'll also may need GM's break out box.

That said, keep in mind that a lot of problems with codes such as you are working with are solved with wiring, connections and grounding problems.

In any case, the Factory Service Manual is your friend. Hopefully, the .pdfs "Dadaroo" has emailed you are pages out of Section 5 of the FSM which pertain to those two fault codes.

Good luck!

 

[dadaroo]

Yes, I gave the exact FSM info which covers both of theses codes together in the same diagnostic write up.

 

[dougelam]

I followed document 684616 thru to step 12 where it states replace EBCM.
I did retest both grounds by drawing 10amps through each and measuring voltage drop.
Both had only .10v and the power supply had .20v on the battery positive circuit but I measured .9v on the ignition 3 circuit.
I moved to the fuse for that circuit and got .4v
I Believe that I may have put too much of a load on that circuit so I will check it live by back probing it when I get my EBCM repaired by

Chevy Corvette Ebcm ABS Module Repair Service 2001 2004 | eBay

 

[dougelam]

Well, I sent my EBCM in for repair at a cost of $100 and did get it back and installed it.
Same codes as before. I guess I will start from square one and recheck all the places that were suggested. Odd thing is that it is a hard code, it never clears for more that 3 seconds where when a wire issue is the cause I thought that it would clear and not return until the vehicle was driven.

Here's the whole story, after replacing the serpentine belt tensioner I pulled out on the road and when it hit 3rd gear the whole front of the car shook just like the front wheel was falling off. it went into loss of power mode, the oil pressure gauge went to zero and the messages starting to scroll. It started to miss and I was barely able to get to the side of the road.

I shut the engine down and waited, restarted and the engine ran real rough along with the service traction and handling messages. I checked under the hood thinking that the belt fell off and cut thru some wires when I heard a ZAP, ZAP, ZAP, ZAP, ZAP I removed the drivers side coil cover and saw #5 plug wire fell off from the coil, I shut it down and plugged it back in. Now the car runs smooth but with the codes and messages.

I drove it home and started to check things out, the belt was where it was supposed to be and I did find the negative battery cable was able to turn on the battery. I checked the bolt and it was tight so I removed it and found it was cross threaded. Replaced the bolt and tried to clear the codes with no luck and that is when I turned to here.

That violent shake was enough to vibrate a loose plug wire off is weird in it self but I guess crazier things have happened.
The car is in real good shape and I believe that the loose ground may have caused a module to fail, the only one left is the PCM!
Who repairs them?
And at what cost

Thanks for listening and again any/all thoughts will be appreciated
Doug

 

[dadaroo]

What did they say what they did to the EBCM? Did they know what your codes were?

 

[Hib Halverson]

I'd say that if you applied a 10-amp current to various ground circuits to "test" them, that was likely a mistake.

I'd stop guessing at "new" ways to test your car's wiring, get a copy of the Factory Service Manual and follow the diagnostic instructions listed for the current codes which are stored in the various chassis modules.

Most who try and second guess diagnostic procedures get into trouble pretty quick as far as cost.

 

[dougelam]

What did they say what they did to the EBCM? Did they know what your codes were?

They did not say, and yes I gave them the same information as I gave you. They did say that GM EBCM's had a known problem with solder at the internal relay.

I'd say that if you applied a 10-amp current to various ground circuits to "test" them, that was likely a mistake.

I'd stop guessing at "new" ways to test your car's wiring, get a copy of the Factory Service Manual and follow the diagnostic instructions listed for the current codes which are stored in the various chassis modules.

Most who try and second guess diagnostic procedures get into trouble pretty quick as far as cost.

With all due respect Hib if you think checking for a voltage drop is new then I don't know where you have been for the last 50 years. Voltage drop was among the first things I was taught in electrical troubleshooting AT the DRC (Dealer Repair Center} in Detroit by Gm instructors. Living in Michigan is handy, I have spent many days at their training center in Warren since 1985. Sometimes for a week at a time

AND if you read the FSM it states in diagnostic aids to check for "A wiring problem, terminal corrosion, or poor connection in the requested torque circuit"

STEP 2 states "Inspect the EBCM ground and PCM ground,making sure each ground is clean and torqued to
the proper specification.

Without testing the integrity of the circuit after that how would you know if a wire is worn thru or corroded somewhere in between?

HA, a strand of wire the size of a human hair will have 0 ohms and will show 12 volts until you put a load on it, This is where the service manual assumes that you know this and have the knowledge and ability to test and diagnose the circuit and come to a conclusion.

So you accused me of making a mistake and guessing, then second guessing the FSM!
There was NO guessing, it is called going to the next level when standard diagnostics where inconclusive. AND I bet every mechanic has had to go there and some wish they knew how

BUT thanks for the insight and I do take all criticism lightly and I DO learn from it
Doug

 

[Hib Halverson]

(quote)


With all due respect Hib if you think checking for a voltage drop is new then I don't know where you have been for the last 50 years.

I apologize for the way I wrote that. When I said "new" I meant a procedure other than what GM may recommend in the Service Manual.

Be careful about applying that much current on the ground side of circuitry associated with the car's various control modules. Also, know that a lot of engine and chassis controls use a 5V reference not 12V. Apply a 12V, 10A current to a component intended to carry a few miliamps at 5V may cause problems.

Good luck.

 

[dougelam]

Good point, thanks again
Doug

 

[dadaroo]

Without a Tech 2 I am afraid we can't determine if you have a EBCM issue or a PCM issue at this point. Wish you were closer we would slap mine into use. PCMs are really cheap and can be had as remans from NAPA, etc for about $150. If that does not fix it you have a good original and spare.

You can buy a new EBCM for around $600 or try and see if another shop can repair it.

If your first shop could truly test the EBCM and deemed it good, then I think your PCM may be the issue.

BUT----

One last try might be to do a continuity test on all the circuits from the EBCM to the PCM to valid they are good. You can also verify if any are grounded.

If I remember, I gave you the Connector views for the EBCM and the PCM. If not, I can provide them.

 

[dougelam]

IT'S FIXED ☺ A year later
I bought a used EBCM from eBay for $275 installed it, cleared codes and waa-laa

I went to my local Chevrolet dealership and borrowed their Tech 2 to confirm the EBCM failure last summer but choose to wait until now to replace it.
I do plan on sending it in this winter for the solder problem as a preventative measure.

Doug

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