Fair warning: The actual vehicle is a 2006 Tribeca, but is pretty identical in many ways to the 3.0R/H6 Legacys and Outbacks. Part my diagnostic is simply comparing the Tribeca measurements and observations to my 2009 Outback H6. I've only owned this Tribeca for a week so I don't know much of the history, and it has a whopping 247,000 miles on it!
Summary: The car's charging circuit (i.e. alternator) does not appear to be working properly. The voltage on a cold start is around 13.3V but drops to 12.2V within a few minutes. The vehicle does not operate well at low voltage. The dash lights flicker and it starts to misfire and eventually stalls.
Observations:
Probably unrelated:
I think the battery is OK. I think the alternator is OK. I think the major connections (battery terminals, alternator output) are connected good enough. The connections all seemed OK unless the 3-pin harness from my Tribeca was corroded and delivering an inconsistent signal on the ECM control or LAMP signals.
Any insight? Or things to check?
A couple quick ideas:
1) Swap tensioners and belts from my Outback over to the Tribeca to make sure everything is spinning fast enough.
2) Re-clean all connection surfaces
3) Is there something drawing a ton of current when the Tribeca is running? Maybe the alternator is simply overloaded. A fun test might be running my Outback and hooking jumper leads over to the Tribeca. Unhook the Tribeca's alternator so the Outback was powering both its own system and the Tribeca. With all accessories off, can the Outback maintain 14V? If so, then the Tribeca is clearly not drawing a ton of excess current when running.
Thanks for any help!
Summary: The car's charging circuit (i.e. alternator) does not appear to be working properly. The voltage on a cold start is around 13.3V but drops to 12.2V within a few minutes. The vehicle does not operate well at low voltage. The dash lights flicker and it starts to misfire and eventually stalls.
Observations:
- Revving the motor appears to boost the voltage higher (13.x range)
- The belt did not appear to be slipping at all.
- The battery has a date of Jan 2016 on it. It appears to hold a charge well enough. It does not drain off overnight due to "dark currents".
- I swapped alternators between my 06 Tribeca and 09 Outback. The Outback runs both alternators just fine, but the Tribeca does not work right with either alternator.
- The battery is around 12.3V when the vehicle is off
- I cleaned and tightened the battery terminals. The positive terminal was initially loose and a problem, but that didn't end up being related to my current issue.
- The voltage at the output of the alternator matches the battery terminal (i.e. not high impedance between the two points)
- I measured the 3-pin connector while plugged into the alternator via "paperclip backprobe":
- The ECM signal to the alternator is high (5.3V, which was the same as my Outback). This means the ECM wants the alternator to be enabled.
- The fused path to the battery appeared fine. The 7.5A fuse was intact and the voltage on this pin matched the battery
- The Lamp signal was about a volt or two lower than the battery/alternator output voltage. The voltage delta seemed to be about the same as my Outback (but the Outback was at the proper 14.3V charging)
- The battery dash lamp lights up when the key is in the On position (vehicle off) and turns off when the vehicle is started. Despite the low voltage when running, the light never turns back on.
Probably unrelated:
- The headlights are always on when the car is running. The headlight switch on the stalk appears to 'ignore' me when I shut them off. But they do dim a slight amount when I switch them off. I did pull the headlight relays just in case they were messing up something else (alternator functionality).
- The ERR SS P0500 code is thrown along with a C code (forget the specific one, but freeSSM says "ABS/VDC component malfunction"). I think the vehicle is missing its right front ABS wheel sensor. I'll look into after I resolve the voltage issue.
I think the battery is OK. I think the alternator is OK. I think the major connections (battery terminals, alternator output) are connected good enough. The connections all seemed OK unless the 3-pin harness from my Tribeca was corroded and delivering an inconsistent signal on the ECM control or LAMP signals.
Any insight? Or things to check?
A couple quick ideas:
1) Swap tensioners and belts from my Outback over to the Tribeca to make sure everything is spinning fast enough.
2) Re-clean all connection surfaces
3) Is there something drawing a ton of current when the Tribeca is running? Maybe the alternator is simply overloaded. A fun test might be running my Outback and hooking jumper leads over to the Tribeca. Unhook the Tribeca's alternator so the Outback was powering both its own system and the Tribeca. With all accessories off, can the Outback maintain 14V? If so, then the Tribeca is clearly not drawing a ton of excess current when running.
Thanks for any help!