'93 ECM Failure: Dead Battery Results
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 8,351
Likes: 75
From: Tampa Bay FL
'93 ECM Failure: Dead Battery Results
My brother-in-law owns a Ruby 40th anniversary coupe. Recently, after winter storage, he found the battery completely discharged. He had a new battery installed; same result... dead... completely discharged. They tried a 3rd... same result.
Off to a more experienced shop that diagnosed a failed ECM. It was causing a major drain on the battery when not running.
The solution proposed by the GM customer service was for the ECM to be rebuilt by a company that specializes in failed ECMs; they are no longer available NEW (according to GM customer service). So, the C4 awaits its rebuilt ECM. $600 for the remanufacture and 1-year warranty once installed.
Is this a common problem? This car has 44K miles, LT1, automatic in event that is relevant.
Thanks for your info/response.
Off to a more experienced shop that diagnosed a failed ECM. It was causing a major drain on the battery when not running.
The solution proposed by the GM customer service was for the ECM to be rebuilt by a company that specializes in failed ECMs; they are no longer available NEW (according to GM customer service). So, the C4 awaits its rebuilt ECM. $600 for the remanufacture and 1-year warranty once installed.
Is this a common problem? This car has 44K miles, LT1, automatic in event that is relevant.
Thanks for your info/response.
Melting Slicks
Joined: Feb 2005
Posts: 2,135
Likes: 0
From: Sebastian Florida
St. Jude Donor '06
What????
There is not any power going to the ECM with the key off.
2nd, $600 is totally ludicrious, SIA will rebuild them for $75.
How was the ECM diagnosed?
How long did it take each battery to die?
You have a short somewhere, you need to find another shop.
There is not any power going to the ECM with the key off.
2nd, $600 is totally ludicrious, SIA will rebuild them for $75.
How was the ECM diagnosed?
How long did it take each battery to die?
You have a short somewhere, you need to find another shop.
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 8,351
Likes: 75
From: Tampa Bay FL
Thanks. I've informed him about SIA. $129.17 includes $50 core charge if ECM they send them is not rebuildable.
Not aware how much the dealer charged for core in that $600. They are expecting a portion back. Granted, the dealer is performing the removal/install and also transferring the vette chip (if they don't rebuild the existing ECM).
To find SIA, I searched on "SIA Corvette ECM". From what I found on the SIA website, they rebuild MANY makes and years of ECMs. Sounds like an incredible bargain. Almost too good a deal. For them to rebuild a Corvette ECM for $80 sounds unbelievable. Most places won't even diagnose a problem (granted the problem is assumed to be the ECM).
I will be interested to see if the ECM rebuild solves their problem (battery draining in matter of several hours).
What I found strange was they had to pay the $600 to the GM dealer upfront... they've not even taken the car to the dealer yet for the ECM removal for shipping of the unit to California for the rebuild.
Thanks for the info. He mentioned he may inquire on what he is getting for all of that $600. The vette will 'sit' at the dealer for a week while it waits for the rebuilt part.
Not aware how much the dealer charged for core in that $600. They are expecting a portion back. Granted, the dealer is performing the removal/install and also transferring the vette chip (if they don't rebuild the existing ECM).
To find SIA, I searched on "SIA Corvette ECM". From what I found on the SIA website, they rebuild MANY makes and years of ECMs. Sounds like an incredible bargain. Almost too good a deal. For them to rebuild a Corvette ECM for $80 sounds unbelievable. Most places won't even diagnose a problem (granted the problem is assumed to be the ECM).
I will be interested to see if the ECM rebuild solves their problem (battery draining in matter of several hours).
What I found strange was they had to pay the $600 to the GM dealer upfront... they've not even taken the car to the dealer yet for the ECM removal for shipping of the unit to California for the rebuild.
Thanks for the info. He mentioned he may inquire on what he is getting for all of that $600. The vette will 'sit' at the dealer for a week while it waits for the rebuilt part.
Safety Car
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From: :45 minutes from everywhere / E-I-E-I-O
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Simple test.
Get the battery charged and pull the ECM fuse. Then wait the appreciate amount of time and see if the battery is dead. If it is discharged, then probably it is not the ECM.
If battery is alive, reinstall fuse. Then wait again and see if it goes dead.
The believe the ECM always has 12 volts on it of keep memory alive and save what it has learned about fuel mixture. Long and short term fuel trim, block learns (BLM).
With the cars of today the computers always need voltage to them. That’s why we check the idle current of about 25ma (.025Amps). Always charge battery at least once a month when not in use.
Get the battery charged and pull the ECM fuse. Then wait the appreciate amount of time and see if the battery is dead. If it is discharged, then probably it is not the ECM.
If battery is alive, reinstall fuse. Then wait again and see if it goes dead.
The believe the ECM always has 12 volts on it of keep memory alive and save what it has learned about fuel mixture. Long and short term fuel trim, block learns (BLM).
With the cars of today the computers always need voltage to them. That’s why we check the idle current of about 25ma (.025Amps). Always charge battery at least once a month when not in use.
Last edited by pcolt94; May 28, 2008 at 09:43 PM.
Melting Slicks
Joined: Feb 2005
Posts: 2,135
Likes: 0
From: Sebastian Florida
St. Jude Donor '06
Sorry Pcolt, the ECM does not always have 12 volts. For memory it has maybe .5 volts to maintain memory. There is no way the ECM drains the battery, unless like I said there is a short. I find it hard to believe that a ECM would drain the battery in so short a time.
The ECM does not get a direct feed of power from the battery, according to the FSM, it gets the power with the key off through the CCM.
You have a grounding issue or short somewhere between those 2 places.
The ECM does not get a direct feed of power from the battery, according to the FSM, it gets the power with the key off through the CCM.
You have a grounding issue or short somewhere between those 2 places.
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Verdad Gallardo
Safety Car
Joined: Feb 1999
Posts: 3,504
Likes: 4
From: Mexico Beach FL
The ECM, like the CCM, does draw current at all times.
But, these computers draw much less current when the vehicle is not being run -- normally, they will not drain a battery unless it hasn't been used for months.
When these computers "wake" up during vehicle use, they draw more current than when asleep.
The ECM is supplied 12 volts from the battery, but the ECM has a regulator circuit inside that regulates the voltage down to 5 volts for most, but not all functions.
Tom Piper
But, these computers draw much less current when the vehicle is not being run -- normally, they will not drain a battery unless it hasn't been used for months.
When these computers "wake" up during vehicle use, they draw more current than when asleep.
The ECM is supplied 12 volts from the battery, but the ECM has a regulator circuit inside that regulates the voltage down to 5 volts for most, but not all functions.
Tom Piper
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Sorry Pcolt, the ECM does not always have 12 volts. For memory it has maybe .5 volts to maintain memory. There is no way the ECM drains the battery, unless like I said there is a short. I find it hard to believe that a ECM would drain the other batterys in so short a time.
The ECM does not get a direct feed of power from the battery, according to the FSM, it gets the power with the key off through the CCM.
You have a grounding issue or short somewhere between those 2 places.
The ECM does not get a direct feed of power from the battery, according to the FSM, it gets the power with the key off through the CCM.
You have a grounding issue or short somewhere between those 2 places.
I agree the ECM should not drain battery unless there is a high resistance short.
In post #1 TedH never gave a time frame when the other batterys went dead. It was not till post #7 that the assumption was made the battery wend dead in a few hours. And that’s what everybody’s been running with since. Post #2 asked how long but there was no answer to that question from TedH.
I also have to correct myself from my original post when I said to pull the fuse. It was misleading because the real fuse you want is under the hood (I believe) which is the one that supplies 12 volts power to the ECM all the time.
The ECM, like the CCM, does draw current at all times.
But, these computers draw much less current when the vehicle is not being run -- normally, they will not drain a battery unless it hasn't been used for months.
When these computers "wake" up during vehicle use, they draw more current than when asleep.
The ECM is supplied 12 volts from the battery, but the ECM has a regulator circuit inside that regulates the voltage down to 5 volts for most, but not all functions.
Tom Piper
But, these computers draw much less current when the vehicle is not being run -- normally, they will not drain a battery unless it hasn't been used for months.
When these computers "wake" up during vehicle use, they draw more current than when asleep.
The ECM is supplied 12 volts from the battery, but the ECM has a regulator circuit inside that regulates the voltage down to 5 volts for most, but not all functions.
Tom Piper
GM indicates idle current (asleep mode) should be under 50 ma. I believe I measured 29 ma on my 94.
