Electrical nightmare.... help!
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Joined: Aug 2004
Posts: 61
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From: Richmond BC
Electrical nightmare.... help!
The problem is that something is draining the battery when the car is not being used. jumping the car will start it and it then runs fine, you can turn it off and then restart it with no problems... But if its off for any length of time longer than about 6 hours, the battery will be too weak to start the car. The battery has been replaced, alternator has been tested and is fine, and the alarm and stereo was disconnected and the problem persists... I have poked around with a multimeter and noticed a 10.5V reading where the "LCD" fuse goes. Anyone know where to get an electrical schematic of the C4? Or better yet, anyone have this problem personally? I'd love a little help on this one...
Pro
Joined: Nov 2006
Posts: 638
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From: Plano TX
The problem is that something is draining the battery when the car is not being used. jumping the car will start it and it then runs fine, you can turn it off and then restart it with no problems... But if its off for any length of time longer than about 6 hours, the battery will be too weak to start the car. The battery has been replaced, alternator has been tested and is fine, and the alarm and stereo was disconnected and the problem persists... I have poked around with a multimeter and noticed a 10.5V reading where the "LCD" fuse goes. Anyone know where to get an electrical schematic of the C4? Or better yet, anyone have this problem personally? I'd love a little help on this one...
Also, you can get the schematic out of the FSM for your year model.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Search will turn up a ton of posts about parasitic battery drain. First, buy at least the electrical diagnosis service manual supplement for your year C4. It has the circuit diagram, explanation of how each circuit works, diagnosis procedure for common problems and sketches of where parts are located. Extremely valuable!
A voltmeter will not tell you about current leakage, you need a milliammeter or an ammeter and they are connected in series with a wire to measure current. GM says C4 leakage current should not exceed 50 milliamps. My 87 draws 27 ma. To measure leakage current remove your negative battery cable and connect your VOM multimeter set to amps or its highest milliamp scale from the cable to the battery post. Now your ammeter is in series with the battery and it will measure leakage current. The meter should be able to read several amps upon hookup because the courtesy lights will come on, and when they time out, leakage current will remain. Pull the courtesy light fuse so you can keep the passenger door open, watch the ammeter while you pull fuses one at a time and any fuse that causes a dramatic drop in current is the circuit that needs further looking into. Early C4's have a bolt behind the battery with 8 red wires with fusible links and you can remove the nut and remove the red wires one at a time while watching the ammeter if you have no luck with the fuses.
Also, whenever you are asking for help, always identify what year C4 you have since they are not identical.
A voltmeter will not tell you about current leakage, you need a milliammeter or an ammeter and they are connected in series with a wire to measure current. GM says C4 leakage current should not exceed 50 milliamps. My 87 draws 27 ma. To measure leakage current remove your negative battery cable and connect your VOM multimeter set to amps or its highest milliamp scale from the cable to the battery post. Now your ammeter is in series with the battery and it will measure leakage current. The meter should be able to read several amps upon hookup because the courtesy lights will come on, and when they time out, leakage current will remain. Pull the courtesy light fuse so you can keep the passenger door open, watch the ammeter while you pull fuses one at a time and any fuse that causes a dramatic drop in current is the circuit that needs further looking into. Early C4's have a bolt behind the battery with 8 red wires with fusible links and you can remove the nut and remove the red wires one at a time while watching the ammeter if you have no luck with the fuses.
Also, whenever you are asking for help, always identify what year C4 you have since they are not identical.
