'09 Subaru Forester CANBUS comm code stored

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Drivability issue-- idle drops out to momentary near-stall but always recovers when disengaging clutch to down shift into 2nd gear and only does it going down into 2nd gear (manual trans). I have run it through the idle relearn process several times and no joy on that issue. Otherwise it idles spot on @ OE spec of 600rpm. Starts as normal, no hard starting but does idle rougher than than usual while coming up to temp. The 2nd gear down shift idle drops also continue after its up to operating temp.

I don't have a check engine light on, but I've got three history codes stored. The CEL has never come on, so I'm baffled that these would not have tripped it.

C0042 - Steering Angle Sensor
C0057 - Communication error on CANBUS between ECU and ABS/VDC module
C0071 - Voltage loss to ABS/VDC module

VDC is stability control which does involve cutting throttle when certain conditions happen, but the idle drop out occurs even when I disable VDC via a button on the lower left of dash.

I have gone over connections and ground wire studs and found everything secure. Battery is about 24 months old, Subaru OEM type bought at dealer, cranks with plenty of power (i.e. not a battery issue), terminals clean and tight. Fuel economy is as normal.

Got me a head scratcher. Don't like glitches that may be living in the electronics or the comm bus. Don't like them a bit.
 
Are you getting ~14VDC across the battery at idle?

I've seen low system voltage (old battery, failing alternator) cause all kinds of weird codes.
 
I'm interested in what you find. I tried doing a google search for the Subaru CANBUS error message and didn't really find anything helpful.

I did find this info http://www.subaruoutback.org/forums/99-d...codes-dtcs.html

The two images don't appear at the bottom, but I believe these are them:

http://s836.photobucket.com/user/ViktorA/media/13290normal_meter_dtc_display-med.jpg.html

http://s836.photobucket.com/user/ViktorA/media/13290mult-information_dtc_display-m.jpg.html

I'd be interested in finding out what caused your issue and what the solution was in case it ever happens to my Subaru.
 
These similar type errors appeared on our 2005 Legacy. Turned out to be a bad voltage regulator in alternator.

We did not get a driveability issue though and these codes are likely unrelated to that.
 
ABS engaged the pump which is a major current draw and the voltage dipped low enough that it almost lost connection with the ECU for a minute amount of time. You might have also been steering as well hence the steering angle sensor code.

I would confirm you have good voltage at the battery & alternator.
 
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Almost got it hung up in some deep snow out in the boonies screwing around a few weeks ago and the ABS was pulsing select wheels to brake them so the opposite wheel could try to get traction (feature of the VDC). That may have done it. I ended up turning VDC off and letting the AWD spin where it wanted to, and made it out without further incident. VDC ain't all its cracked up to be, in deep snow.
 
Yes exactly...if I am intent on trudging through as you were in deep snow any VDC/ESP/TCS has to come off in any AWD car. It will get you stuck and it doesn't let the wheels spin. You need that so you can maintain forward momentum.
 
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If this has a "traditional" cable throttle your TPS might be going out, so it doesn't know your foot is off the gas, and that it needs to control the idle.

If the reading remain plausible, no code.
 
Originally Posted By: JTK
Are you getting ~14VDC across the battery at idle?

I've seen low system voltage (old battery, failing alternator) cause all kinds of weird codes.


I tested this today (analog multimeter), all looks okay:

engine off ...........................12.9v
@ idle, no accessories on ...14.5v
@ idle, accessories on* ......13.5v

* HVAC blower on high, radio vol near max, headlights hi beam, rear window defrost
 
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