Vehicle: 1996 Acura TL, 2.5L, 5 cylinder.
Complaint: Vehicle loses electrical power depending on how long it’s driven and the electrical load on the alternator.
The vehicle was towed to the shop with a totally failed electrical system. Meaning no power at all.
Found 100 amp battery fuse blown.
Replace the fuse and vehicle starts.
Test charging system: No output from the alternator.
The alternator output is controlled by the ECU and the Electrical Load Detector. Here’s the wiring diagram. http://www.justanswer.com/uploads/Themaxview/2008-08-05_151314_acc.PNG
Remove the alternator and bench test it. Voltage regulator no good. Replace the alternator. Alternator now puts out 14.5 volts at idle but as the electrical demand becomes greater voltage from the alternator drops to battery voltage.
Hook a scanner up to monitor voltage control and output. Scanner cannot communicate with vehicle. Bad ECU.
Replace the ECU and now scanner can communicate with vehicle.
Check charging system with scanner and all works properly except for output from alternator.
Check for a failed ELD. Here’s that procedure. http://www.rywire.com/catalog/images/troubleshooting/code20-eld-test.jpg
ELD checks good.
If you disconnect the white/green wire from the back of the alternator it removes the ECU and the ELD from the circuit and the charging system operates as a conventional charging system. Remove the wire, still the same.
Now after doing all this diagnostics and repair, what is preventing the alternator from keeping up with the demands of the electrical system?
And when I tell you, you won’t believe it. The son didn’t when I showed him.