[TWX]

Hey all,

The buddy that ended up with my old Stratus has had a persistent problem with the battery draining, if he doesn't drive the car daily then the battery drains so far it won't start. He's changed batteries several times.

Today we went through with an ammeter between the positive battery terminal and the positive cable. Got a steady ~0.08A draw. Started pulling fuses and relays in order. When we got to the TCM 20A fuse under the hood we dropped to basically negligible draw. Did some reading and pulled and reinstalled it and the relay a few times and when the fuse is present that draw is present, when the fuse is pulled the draw drops to negligible, and the TCM relay seems to have no bearing on the amperage. Relay clicks whenever the fuse is reinstalled. All of this was with the key out and all doors shut.

Not quite where to go from here. I'm tempted to recommend that he pull the TCM fuse overnight and see how severe the draw problem is in the morning, but that doesn't really help us fix the problem. Suggestions would be appreciated.

 

[Bob Lincoln]

80 mA is a reasonable current draw for all the electronics, and will not drain the battery overnight, unless the battery is no good. So I would not expect a short circuit or device failure. Something else is going on.

 

[AllanC]

The TCM fuse in the PDC ( power distribution center) should be fuse #3, 20 amp. This provides power to the load side of the TCM relay in the PDC. Fuse #3 also provides constant power to the TCM. You might unplug the electrical connector at the TCM and make sure there are no shorts between any of the receptacles in the connector. You should NOT hear / feel the TCM relay click when installing fuse #3 with the ignition switch off.

I agree with Bob L that 80 milliamp (0.08 amp) draw should not drain the battery overnight such that you cannot start the engine. Try and remove the #3 fuse overnight and see if the vehicle starts next day. If yes then you have isolated the problem to the TCM module or the wiring. If no then you will need to search elsewhere.

Another possibility is that the alternator diodes are leaking a small amount of current to ground. Diodes have battery potential on one side and chassis ground on the other side but act as a "one way valve" so as to not allow battery drain.

 

[TWX]

Okay. I'd already suggested that he pull the fuse overnight to see if the problem persists in the morning or not. Given that relay-click with the key out I also suggested that something in the ignition key in the column could be a problem too, maybe we'll have to play with that again another day, along with checking the TCM connector on the harness.

I haven't really worked with alternators with integrated voltage regulation, I'm more used to the older kind where a VRM was mounted to the firewall. Any suggestion for how to test those diodes short of replacing the alternator?

 

[Bob Lincoln]

Voltage regulator is in the ECM, not in the alternator.
The relay click may be something other than the TCM that's powered by the same fuse.
If the alternator has a shorted diode, the current draw should be measurable in the manner that was already done, and should have shown a high amperage draw. A shorted diode can kill a battery overnight, but draws several amps or more. Also, it will not reach full charging voltage at idle. I had a shorted diode once, killed the battery overnight, and at idle the voltage would not go above 13.3 volts. 14.0 volts was normal.

 

[AllanC]

. . . . I haven't really worked with alternators with integrated voltage regulation, I'm more used to the older kind where a VRM was mounted to the firewall. Any suggestion for how to test those diodes short of replacing the alternator?

Remove the positive battery cable at the battery. At the alternator there is a larger diameter wire which carries battery potential. Remove that wire. Use a volt-ohm meter set to measure continuity. Touch the positive meter lead to the alternator battery terminal and the negative lead to a clean spot on the alternator case. You should see an open circuit on the meter. Any resistance reading indicates a leaking / failed diode. Now reverse the meter leads. Negative lead places on the alternator battery terminal and positive on the case. You should have a meter reading.