Electrical: Parasitic Draw vs New Battery [Solved]
08-29-2014, 01:46 PM
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Electrical: Parasitic Draw vs New Battery [Solved]
First time posting here, long time lurker
So after 2 1/2 years of owning my 2004 Z, I had my first real major problem last week. When I looked through the forums for a solution, I saw a lot of people with the same issue, sometimes spending hundreds of dollars in diagnostics, but no threads that really had a conclusive answer. So I figured it couldn't hurt to document my case and what was needed to solve it.
tldr: problem was my battery. It needed to be replaced. See story for symptoms and troubleshooting process. Estimated diagnostic time: 30 mins - 1 hour
Symptoms: After sitting all day in the hot sun, I went to start my Z to leave work for lunch, and my engine was slow to turn over. It eventually started, but clearly my battery was suffering. I let the car run for 15 minutes to allow the alternator to charge the battery, but despite this, my starter was reduced to clicks by the time I left for home. A jump later I was back on the road without issue. Attempting to start it the next day, same problem; just clicks when I turned the key. What initially threw me was how sudden the problem came on; I never noticed problems relating to a low battery before this. I recently installed a new exhaust and cats too, so now I was thinking "oh great, I nicked a harness, or grounded something that shouldn't be grounded." So my initial thought process was to diagnose a parasitic draw on my electrical system.
Diagnostics: To diagnose a parasitic draw or dead battery, you will need a multimeter or ammeter, 10mm wrench, and a pair of pliers to remove fuses
Set the multimeter to Direct Current and milliamps. If you have multiple inputs for the leads, make sure you are using the 10amp or higher fused port, otherwise you will be repairing more things than just your car.
Disconnect the negative (black) terminal from the battery, and make sure it is not making contact with the frame or anything that could be grounded.
Place the leads of your multimeter between the negative battery post and the wire you disconnected. We are detecting very small changes in the electrical circuit, so the goal here is to monitor all current through the multimeter. You will now have something like the below picture (I took the cover off the main fuse box for diagnostics).
Once your multimeter has a reading, you will need to wait a few minutes for your car's computer to go to sleep (took mine 30 minutes). Once you see a drop in the reading (see below for expected readings), you need to remove fuses one at a time until your multimeter reading drops to a tolerable level. Don't forget your z also has an additional fuse box under the driver-side dash, to the left of the dead pedal.
Once you have located the culprit fuse, you will then have to troubleshoot the circuit that fuse is connected to, but this will give you a good starting point. Here are the readings you are looking for:
80 -100mA: The car's computer is in a ready state, drawing from the battery
35 - 40mA: we want to be under this threshold, anything over this after the computer has gone to sleep means there is a significant draw that can drain your battery
14 - 20mA: This is a good reading after the computer has gone to sleep. You will likely never read anything lower since there are various systems in the car that still use the battery to "stay alive" after the car has been turned off (these include your radio settings, tire pressure sensors, tachometer, "listening" for the keyfob, etc.)
My mistake while doing this was I left the keyfob in the passenger seat the first time I was troubleshooting. This cause the car's computer to stay awake and draw 90mA from the battery until I removed the BCM fuse (the big green one in the picture), at which point I saw a 60mA drop for a false positive. Replacing the BCM would be expensive, and most of the threads I saw with similar findings had no resolution, so I decided to troubleshoot a second time. This time I left my keyfob in the furthest room in my house from the car and waited 30 minutes for my computer to go to sleep after connecting the multimeter.
Boom. my reading was 14mA. I didn't have a parasitic draw, and the only other possible problem was my 10 year old original factory battery. I took my battery to O'Reily and they confirmed it was no good (protip: charge the battery before taking it in so they can give you a diagnosis without having to wait).
So why go through all the trouble I did? Well if I guessed it was the battery and instead it was a parasitic draw, I would be out 130$ and the problem would resurface again in a week, requiring more of my time, and more $$ for damaged components.
Hope this helps someone
So after 2 1/2 years of owning my 2004 Z, I had my first real major problem last week. When I looked through the forums for a solution, I saw a lot of people with the same issue, sometimes spending hundreds of dollars in diagnostics, but no threads that really had a conclusive answer. So I figured it couldn't hurt to document my case and what was needed to solve it.
tldr: problem was my battery. It needed to be replaced. See story for symptoms and troubleshooting process. Estimated diagnostic time: 30 mins - 1 hour
Symptoms: After sitting all day in the hot sun, I went to start my Z to leave work for lunch, and my engine was slow to turn over. It eventually started, but clearly my battery was suffering. I let the car run for 15 minutes to allow the alternator to charge the battery, but despite this, my starter was reduced to clicks by the time I left for home. A jump later I was back on the road without issue. Attempting to start it the next day, same problem; just clicks when I turned the key. What initially threw me was how sudden the problem came on; I never noticed problems relating to a low battery before this. I recently installed a new exhaust and cats too, so now I was thinking "oh great, I nicked a harness, or grounded something that shouldn't be grounded." So my initial thought process was to diagnose a parasitic draw on my electrical system.
Diagnostics: To diagnose a parasitic draw or dead battery, you will need a multimeter or ammeter, 10mm wrench, and a pair of pliers to remove fuses
Set the multimeter to Direct Current and milliamps. If you have multiple inputs for the leads, make sure you are using the 10amp or higher fused port, otherwise you will be repairing more things than just your car.
Disconnect the negative (black) terminal from the battery, and make sure it is not making contact with the frame or anything that could be grounded.
Place the leads of your multimeter between the negative battery post and the wire you disconnected. We are detecting very small changes in the electrical circuit, so the goal here is to monitor all current through the multimeter. You will now have something like the below picture (I took the cover off the main fuse box for diagnostics).
Once your multimeter has a reading, you will need to wait a few minutes for your car's computer to go to sleep (took mine 30 minutes). Once you see a drop in the reading (see below for expected readings), you need to remove fuses one at a time until your multimeter reading drops to a tolerable level. Don't forget your z also has an additional fuse box under the driver-side dash, to the left of the dead pedal.
Once you have located the culprit fuse, you will then have to troubleshoot the circuit that fuse is connected to, but this will give you a good starting point. Here are the readings you are looking for:
80 -100mA: The car's computer is in a ready state, drawing from the battery
35 - 40mA: we want to be under this threshold, anything over this after the computer has gone to sleep means there is a significant draw that can drain your battery
14 - 20mA: This is a good reading after the computer has gone to sleep. You will likely never read anything lower since there are various systems in the car that still use the battery to "stay alive" after the car has been turned off (these include your radio settings, tire pressure sensors, tachometer, "listening" for the keyfob, etc.)
My mistake while doing this was I left the keyfob in the passenger seat the first time I was troubleshooting. This cause the car's computer to stay awake and draw 90mA from the battery until I removed the BCM fuse (the big green one in the picture), at which point I saw a 60mA drop for a false positive. Replacing the BCM would be expensive, and most of the threads I saw with similar findings had no resolution, so I decided to troubleshoot a second time. This time I left my keyfob in the furthest room in my house from the car and waited 30 minutes for my computer to go to sleep after connecting the multimeter.
Boom. my reading was 14mA. I didn't have a parasitic draw, and the only other possible problem was my 10 year old original factory battery. I took my battery to O'Reily and they confirmed it was no good (protip: charge the battery before taking it in so they can give you a diagnosis without having to wait).
So why go through all the trouble I did? Well if I guessed it was the battery and instead it was a parasitic draw, I would be out 130$ and the problem would resurface again in a week, requiring more of my time, and more $$ for damaged components.
Hope this helps someone
08-31-2014, 09:12 AM
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Not really sure, it had to have been pretty low since I was unable to start the car. Probably around 8 volts. Either way it shouldn't affect the readings since we are detecting very small changes in current (unless the battery is completely dead)
08-31-2014, 07:43 PM
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Read the full post first before you try to tear it apart. ty
I recently installed a new exhaust and cats too, so now I was thinking "oh great, I nicked a harness, or grounded something that shouldn't be grounded." So my initial thought process was to diagnose a parasitic draw on my electrical system.
09-01-2014, 10:44 AM
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Good job on the troubleshooting and your results. One thing I've noticed over more recent years is that quite often a battery will give up with little to no warning. In 'the old days' more slower cranking events before 'the end' seemed to be the rule. Dan Mpls. Mn.
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