[Dispatch20]

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:

• 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!

 

[plain OM]

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).

Are those the DRLs? They would be slightly less bright than the full headlights. When the engine is running, and the main headlight switch is OFF, what happens if the parking brake lever is pulled up; do the headlights go off? (I presume the lights did not work with the relays removed!)

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.

(Good that you have the Outback to compare to.)

The problem is in the Tribeca's electrical system, not the alternator itself.

There could be a problem in the ground circuit. A bad ground can cause the alternator output to be low.

Using a digital multimeter to make measurements? If so, with some electrical loads switched on, such as the full headlights, and perhaps the cabin heater fan, and with the engine running at 1000+ rpm, measure the voltage at the following points:

Battery negative post (not the cable clamp) to alternator case, to engine block, and to a good ground connection on the car body.

I'm not familiar with the Tribeca wiring, especially at the fuse box. But if it's the same as the Outback, also measure between the battery positive post and either side of the large main fuse in fuse box (the one which, in the Outback, has two posts with nuts on them holding the fuse in place). Also measure between the alternator output post and the same two sides of the main fuse.

Ideally all would be less than 0.1 V, but should be not higher than 0.2 V. (Use the lowest range on the meter.)

If any of these are higher than they should be, there's a ground wire/connection problem that could be affecting the alternator output.

(Note, these measurements are made with higher currents flowing through the connections, and we're looking for relatively small voltage drops, rather than measuring, for example, the voltage across the battery, and from the alternator output terminal to ground, with the engine off, or idling.)

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". . . . The battery is around 12.3V when the vehicle is off

12.3 V of course, is low, but if the alternator doesn't do much more, that's understandable. You've swapped the alternators; have you tried swapping the batteries, just to eliminate any possibility the battery is the cause?

 

[Dispatch20]

Are those the DRLs? They would be slightly less bright than the full headlights. When the engine is running, and the main headlight switch is OFF, what happens if the parking brake lever is pulled up; do the headlights go off? (I presume the lights did not work with the relays removed!)

This gets weird. I think my parking brake sensor/switch might have gotten stuck or something. After kicking the parking brake pedal repeatedly, it seems to work just fine now. Yes, Tribeca has a kick brake like a truck. Previously, it was sort of random on whether they shutoff. Initially, they didn't shut off at all. So yes, they are just the DRLs!

Pulling the relays did kill the lights, though.

(Good that you have the Outback to compare to.)

The problem is in the Tribeca's electrical system, not the alternator itself.

There could be a problem in the ground circuit. A bad ground can cause the alternator output to be low.

Using a digital multimeter to make measurements? If so, with some electrical loads switched on, such as the full headlights, and perhaps the cabin heater fan, and with the engine running at 1000+ rpm, measure the voltage at the following points:

Battery negative post (not the cable clamp) to alternator case, to engine block, and to a good ground connection on the car body.

I'm not familiar with the Tribeca wiring, especially at the fuse box. But if it's the same as the Outback, also measure between the battery positive post and either side of the large main fuse in fuse box (the one which, in the Outback, has two posts with nuts on them holding the fuse in place). Also measure between the alternator output post and the same two sides of the main fuse.

Ideally all would be less than 0.1 V, but should be not higher than 0.2 V. (Use the lowest range on the meter.)

If any of these are higher than they should be, there's a ground wire/connection problem that could be affecting the alternator output.

(Note, these measurements are made with higher currents flowing through the connections, and we're looking for relatively small voltage drops, rather than measuring, for example, the voltage across the battery, and from the alternator output terminal to ground, with the engine off, or idling.)



12.3 V of course, is low, but if the alternator doesn't do much more, that's understandable. You've swapped the alternators; have you tried swapping the batteries, just to eliminate any possibility the battery is the cause?

I seem to have good ground connectivity. I am using a digital multimeter. The resistance between the points you mentioned was low, and when loaded I didn't get any significant voltage drops. To do the voltage drop measurements, I did turn on the headlights and high beams, radio, & hvac fans.

There's some more weirdness that I'll need to mess with tomorrow. When I start the car completely cold, the alternator outputs 14.3V. After about a minute or so, the voltage drops lower and lower. Eventually the voltage drops below 12V as the battery and alternator combined are unable to provide the power needed to idle. I'm not sure if this is related to the RPMs dropping as the idle approaches the 600rpm steady state point, or whether some huge electrical load presents itself.

Caveat: As I'm just a single person, I can't rev the motor and use my multimeter at the same time to watch the voltage.

I am suspecting it's a huge electrical load. When I hook jumper cables from my other H6 over to the Tribeca, there is a significant (.5V) drop over the jumper cables as it provides juice to the Tribeca. The Tribeca sees 13.5V at best using the combined power of the other H6 vehicle (its alternator & battery) and it's own battery and alternator. Maybe this is a bad test due to too many variables that could draw load: Tribeca battery, Outback battery, potential mystery load.

Some next steps:

• Double check and clean all the grounds
• Verify the observation that the alternator is at 14.3V on a cold start for the first minute.
• Try to isolate any large loads on the Tribeca by pulling relays and fuses
• Drag my wife out to the garage to rev the engine so I can watch the voltage
• Consider borrowing a current probe (big loop style) from work (engineering shop) so I can measure the alternator output DC current on my Tribeca and compare to my Outback

All signs indicate the Tribeca alternator is good and the control inputs (ECM, lamp, fused battery voltage) are proper. It just looks like the alternator can't keep up with the load at idle. One thing I noticed that really seems to take down the voltage is pressing the brake pedal. Lighting up the brake lights almost stalls the engine. Or maybe a vacuum leak or brake booster issue almost stalls the engine. The brake pedal is really squishy and doesn't hold pressure per the spec.

 

[plain OM]

The battery is about the only part that is connected to the alternator without low level fusing and that could draw the voltage down. (The alternator-to-battery circuit has a large 125 Amp main fuse, whereas most other circuits have fusing at much lower levels.)

Have the battery checked, or perhaps just put the Outback battery in the Tribeca (if it fits) and see what happens. Or, put the Tribeca battery in the Outback. It's the one major component that has not been swapped/checked, and is leaving a gap in what we/you know, for sure.

 

[Dispatch20]

The battery is about the only part that is connected to the alternator without low level fusing and that could draw the voltage down. (The alternator-to-battery circuit has a large 125 Amp main fuse, whereas most other circuits have fusing at much lower levels.)

Have the battery checked, or perhaps just put the Outback battery in the Tribeca (if it fits) and see what happens. Or, put the Tribeca battery in the Outback. It's the one major component that has not been swapped/checked, and is leaving a gap in what we/you know, for sure.

Good point. I'll swap over a known good battery and try it all again. I saw you mention that above and I forgot to address it. I have a brand new battery in my Outback.

When I got the vehicle a week ago ($700 purchase price, had to tow it home), the positive terminal was weakly held on because it was missing the plastic terminal spacer that some smaller diameter terminals need in our cars. The terminal most certainly wasn't on sufficiently to always be charging the battery. It's possible they left this battery half drained/fully drained for the past 1.5 years and killed it all due to a poor terminal connection.

I can't imagine what could draw so much current without popping a fuse.

Thanks for the ideas so far!

 

[Dispatch20]

Update: I put my Outback's new battery into the Tribeca, and it didn't change anything. It was worth a shot!

Here's the behavior I'm seeing:
When I cold started the Tribeca, the alternator was putting out 14.7V and dropped down to 14.3V after about a minute. The vehicle was idling around 750RPM, which is typical when the H6 isn't fully warmed up. After another 5 minutes or so, the RPM dropped down to 575RPM and the alternator was putting out 13.8V. The H6 RPM idle spec is 650RPM so it's possible the reduced RPM was lowering the alternator output. I believe the vehicle would have stayed at this low idle and lower alternator output state indefinitely.

This is where things get weird. The vehicle was idling mostly fine (as described above), but the second I tapped the gas pedal the car stalled out. To get the car running again, I'd have to hold the pedal at mid-throttle just like an old non-fuel injected car! At this point, modulating the throttle to get to a specific RPM was very hard. And when I revved the car to 3k RPM the alternator output was only 13.8V. I would have expected 14-14.7 at the higher RPM.

So perhaps the throttle body is gunked up and not responding correctly? Or maybe there is an idle intake control valve issue (not even sure the H6 has one)? It seemed in a reasonable idle state until it the vehicle got warmed up and the throttle was moved. After that, the car struggled to ever idle and mostly stalls out. If it does idle, it is at 500-550RPM which is far too low, and the car voltage is from 11.5V - 12.3V which suggests the alternator is tapped out or not even working. If I wait a day and start the car again from dead cold (or wait ~ an hour), it goes back to the voltage being happy and idling smooth although 75RPM below spec. Again, the second I change the RPM at all things run terribly.

I did look at RomRaider Logger to see if any fuel learning was way out of whack. Everything looked fine at quick glance. There are no check engine codes other than the P0500 ABS wheel sensor. The vehicle isn't misfiring through any of the wackiness.

 

[bheinen74]

someone replaced the OEM alternator with a parts store junk perhaps?
or thjey swapped a H6 outback alternator in there....that is why your h6 Outback still likes this alternator.
if so, then you need to source a OEM alternator for a Tribeca/

 

[Dispatch20]

someone replaced the OEM alternator with a parts store junk perhaps?
or thjey swapped a H6 outback alternator in there....that is why your h6 Outback still likes this alternator.
if so, then you need to source a OEM alternator for a Tribeca/

The Tribeca and Outback H6 use the same alternator. You can swap them freely. I don't think it's an alternator issue at this point, and both of the ones I used were Mistubishi OE. The Tribeca is basically an Outback H6 with a different body. Both use the EZ30D and 5EAT. Under the hood is pretty close to the same. I did quickly spot some differences like the radiator & vacuum hoses, but it's 95% identical in there.

My next things to try:

• Clean out electronic throttle body butterfly
• Swap throttle bodies with my Outback
• Look at accelerator angle sensor inputs (and other throttle related sensor values) and compare to my Outback

 

[bheinen74]

great info, thanks i didn't know they were same.

 

[plain OM]

No IAC valve on the drive-by-wire engines.

Inability to idle. . .

Vacuum leak would be a possibility -- has more effect when the throttle plate is near-closed for idle rpm, but has decreasing effect as the throttle opens for higher idle speeds.

Under what conditions did you use Romraider? Were you able to monitor the A/F Correction and A/F Learning (I believe there's one of each for both banks) while the engine was idling poorly? (Typically, with an intake leak, one or both will be unusually positive, but appear to go down when the throttle is advanced.)

A very dirty throttle body/plate could also affect idling that way, but it's somewhat puzzling why the ECM, monitoring the rpm, doesn't advance the electronically-controlled throttle to compensate.

I don't have specs for the 2006 B9 engine and, especially, the alternator, and how they differ from the H6 Outback of that year or your 2009 H6. I'm not sure that the H6 alternator is so different that it would not work properly in the B9. There might be a different current spec alternator in the B9, but I don't think we're dealing with an excessive load. Nevertheless, I can't totally discount the possibility of the alternator not being the right one.

 

[Dispatch20]

The alternators are identical. Same part # 23700AA510.

I did look for a vacuum leak via A/F correction and learning. However, they kept in range (<10%) at both idle and at revs. Learning stayed at zero. That was good evidence I didn't have a vacuum leak.

I agree on thinking the ECM should just adjust the rpm higher. One oddity is that I attempted to add +300 idle rpm via freessm "adjustments". The car didn't respond to this, and I know the h6 is capable of listening to that.

I'm starting to wonder if the CEL for the p0500 is putting something into a failsafe mode and obscuring the results. maybe i should fix that first.
.

Sent from my SAMSUNG-SM-G890A using Tapatalk

 

[plain OM]

Good on the alternators. I think the alternator possibility is down the list now.

I hadn't focussed on the P0500, but after all this I think you're on the right track.

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.

Based on the Failsafe conditions in the attached (which is from my 2007 FSM, but should be very similar if not the same for the B9), when the code is set, the engine is indeed affected.

 

[Trig]

Other fuel injected vehicles I've owned or had experience with (weren't Subaru), that had an air/vacuum leak have had a high idle speed.
It appeared that the correct fuel-air mixture has priority over idle speed and other factors. The high idle speed was the result of the
emission control system adding fuel to keep the mixture ratio correct (more air (leaking in) results in more fuel requested).

Trig

 

[Dispatch20]

Update: Solution found! I cleaned out the throttle body and it fixed the low idle, stalling, and dropping voltage.

The alternator puts out a steady 14.3V now and revving the engine doesn't make it go berserk. I guess the low idle just wasn't enough to keep the alternator working properly. I'm really not sure about it.

And since I lost some coolant when I removed the throttle body, I have air in the system. These H6's really drive me nuts when getting the air out.. Every time I lose coolant the thermostat likes to stick closed and the bottom hose gets full of air. This means water never circulates in the radiator regardless of water temperature.

Also of interest is that the Bank 2 front O2 is suggesting a vacuum leak on that side (or a lazy front O2). When cold it all runs OK, but at warm the A/F Correction pegs at 35% and the front O2 reads 15.x AFR, which triggers a lean CEL. The fun continues.