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Discussion Starter #1
So I decided to test my voltage this weekend cause my ficm voltage on my cts fluctuates quite a bit with the lowest value I have seen was 44.0 volts.

I tested the voltage on the screw as said in the testing procedure and it was at 48.2 at idle and 47.7 at 1800-2000 rpms but the cts display would drop down to 46 volts.

Now I have a 4 pin ficm is that screw the only spot to test the voltage at? Where does the computer get its reading from? I didn't do the test completely cold because I was mainly worried about what it was showing while driving.

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Test it while cranking.

But 44 volts indicates either your FICM or batteries are bad
 

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Discussion Starter #3
When I was cranking it was at 47.8 and then went to 48.2 per my multimeter. This is why I asked cause my cts fluctuates quite a bit but the multimeter stayes in pretty much the same voltage.

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How old are your batteries?
 

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Good question I bought the truck 3 months ago so I don't know but I do know they are the same type and size and after 5 hours of sitting they are at 12.79 volts (terminals disconnected) I am gonna have them load tested this weekend along with the alternator. I need to test it cold so I will do that tomorrow morning before work.

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Are they motorcrafts?
 

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:popcorn2: My money is on the FICM starting to go.

I didn't test my voltage on the pin but it started with what you describe. Fluctuating while driving and slowly getting lower and lower readings. Then while starting it started to get lower and lower. Now it's throwing a code and getting replaced today.
 

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Honestly, I don't see anything wrong with your numbers. Shoot, I have a rebuilt 58v ficm, new ficm harness, a brand new 220A powerbastards alternator and two brand new interstate megatrons. I've even went thru and done "the big 3" upgrade and I'm still seeing readings as low as 42v KOEO when engine is cold. At the same time, the battery voltage is going as low as 11.5v. I'm guessing the glow plugs are drawing it down. When its warm, FICM voltage flucuates between 47.5-48 and battery voltage flucuates between 13.5-14.3. I'm wondering if I'm missing something here :dunno:
 

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If you are seeing 42v KOEO you have some issue somewhere. Even cold.

With your combo you should never see below 47.5 if your FICM is functioning properly
 

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Discussion Starter #10
They are interstate batteries. The thing that gets me is the cts fluctuates between 45.5-48 but the multimeter stays at 48 weird to me but it is what it is. Just wondering why there would be different readings unless the computer reads from somewhere else.

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Interstate batteries are garbage. Have been for the last decade:doh:
 

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If you are seeing 42v KOEO you have some issue somewhere. Even cold.

With your combo you should never see below 47.5 if your FICM is functioning properly
Thats what I thought...Any suggestions? The only other thing I can figure is one or both of the Brand new batteries are junk. I know swamps programs their 58v FICM's to read in the 48v range. Could it just be something in "the programming" I emailed them and here is the response.

"Dropping 3-4 volts during cold startup is perfectly normal. On a fully warmed up engine, the FICM draws 6-8 amps at the 12 volt input/supply. During cold startup, this can increase to as much as 34 amps, and the power supply in the FICM just can't supply enough current, so the voltage drops slightly.
That's assuming a constant 13.8 volts at the supply; drop the supply voltage to 11.5 like you saw, and the output voltage / current will drop even more.
Everything is just fine!"
 

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Discussion Starter #13
I know they are was hoping to wait change them around november before the snow comes.

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Since my battery replacement Ive never seen below 47.5 cranking.

Start by cleaning your battery terminals
 

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My terminals are spotless. I even use the spray terminal protector on them. I'm going to go get the batteries tested this morning and I'll let you guys know what I find out. This might be interesting. If they are weak, your theory on interstate batteries will be confirmed on my end. Stand by....
 

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My terminals are spotless. I even use the spray terminal protector on them. I'm going to go get the batteries tested this morning and I'll let you guys know what I find out. This might be interesting. If they are weak, your theory on interstate batteries will be confirmed on my end. Stand by....
make sure they disconnect them COMPLETELY when they test them
 

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Batteries tested good. Tested each one individually disconnected. One other thought. What is the story of the fuel heater? Being that mine is an '03, would the fuel heater be drawing amps, thus causing everything else to show low? Didn't they discontinue use of the fuel heater after '03? I pulled the 30A fuse and the relay for the fuel heater just now. We'll see in the morning.
 

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I just finished swapping mine out. With everything cold, reading 45* EOT and 50* ECT, I had 45V on the old FICM. With the new FICM (which has been outside since Friday and cold as well) I had 48V KOEO, 48V cranking and 48V running. Starting the truck under the same conditions with the old FICM in I would be seeing 35-45 volts cranking and running. My voltage was doing the same as the OP (on my CTS) about 5 weeks ago. Once it started showing below 45V once in a while it only took 2.5 weeks to cause a miss once in a while and some light smoking with voltages between 40 and 45 consistently. In the last week (while trying not to use the truck) the voltage fell off another 4-8 volts depending on the temps and I haven't seen 48 volts at any time for two weeks now.

Even with a difference between a multimeter and the CTS I would be that it's the beginning of the end for your FICM.
 

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How old are the batteries. Wouldnt be the first time Ive seen bad batteries pass a load test.

Most load testers only put a 100amp load on. Our trucks put way more than that on cranking
 

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:popcorn2: interesting this one i like to see if it makes a difference.

i have -03 Excursion but i dont think i can un plugg it for next 6 months
cause it starts to be 45 F* mornings and it drops fast... expecting long perioid of 32*F to -30F* :thumb:
 
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