The guy that works on my old cars has a mystery problem with a '99 SLS that I told him I'd try to help diagnose, and am looking for some help getting this figured out.
When the key is put into the ON position but the car is not started, the cluster gauges (including the fuel gauge) sweep to their normal positions, the radio lights up, and all is normal.
When the car is started and key is dropped to the ON position for running, the gauges all sweep and go to running position, but the fuel gauge drops to zero and stays there, and the radio does not come on.
Here is the really weird part--if he disconnects and reconnects the battery, everything works NORMAL for a little while and then eventually goes back to the exhibited behavior. The amount of time before failure returns seems to be related to outside temperature (faster when hotter).
Looking around, it seems to me that the fuel gauge problem can be explained by a faulty sender in the ballast pump. I'm guessing that a relay is activated when the car starts that drives the ballast pump, which would explain why the gauge works when the key is ON but engine is OFF, but does not work when engine is ON. A faulty relay may also explain the situation with the battery connection. However I don't see how the radio fits into this.
Anybody got any information that would fill in the gap here? How is the ballast pump powered, by the BCM or a relay or what? How would this be affected by heat?
When the key is put into the ON position but the car is not started, the cluster gauges (including the fuel gauge) sweep to their normal positions, the radio lights up, and all is normal.
When the car is started and key is dropped to the ON position for running, the gauges all sweep and go to running position, but the fuel gauge drops to zero and stays there, and the radio does not come on.
Here is the really weird part--if he disconnects and reconnects the battery, everything works NORMAL for a little while and then eventually goes back to the exhibited behavior. The amount of time before failure returns seems to be related to outside temperature (faster when hotter).
Looking around, it seems to me that the fuel gauge problem can be explained by a faulty sender in the ballast pump. I'm guessing that a relay is activated when the car starts that drives the ballast pump, which would explain why the gauge works when the key is ON but engine is OFF, but does not work when engine is ON. A faulty relay may also explain the situation with the battery connection. However I don't see how the radio fits into this.
Anybody got any information that would fill in the gap here? How is the ballast pump powered, by the BCM or a relay or what? How would this be affected by heat?
