2008 V6 DBW Failed and Limp Mode

[Steve108]

Last night I was driving to see family on the highway, about a 2 hour drive no issues. As soon as I cancelled the cruise control on the off ramp I got a CEL, PSM fail, PHC unavailable, very rough idle and limp mode. Continued to my destination with what power it had left and checked the codes: P2103, P0638, P2100, P2101. I let the car sit for a couple hours and tried again, still in limp mode.

I have access to some tools here but no service manual. Any thoughts on things I can try? I am going to look for loose connections at the throttle body and gas pedal and check for carbon buildup inside the TB. Beyond that I'm pretty new to DBW.

[Steve108]

More symptoms but no progress. I cleared all the codes and turned the key on with the engine off. It seems like the throttle body will respond sometimes, and for a little while it let me open and close it repeatedly with the pedal, so I plotted the response with my ODB scanner:



Which I thought looked pretty good, so I started the car. The throttle did respond, but it was running awful, black smoke, very rough, backfiring in the intake, etc. I checked codes again and had all kinds of misfires:



I shut it off and started to check the throttle again. I managed to catch it going in to limp mode. You can see it responds correctly at first, and then for some reason the throttle plate snaps shut and stops responding. I am guessing this is a fail safe condition:



I would have expected to see some kind of spike or disagreement between the sensors before it failed, but they all look reasonable, at least at whatever sample rate this cheap OBD adapter uses.

I started it up again to park it, now the engine is not missing, sounds good, but idling erratically. The throttle does respond to the pedal but not smoothly. Here is the throttle body vs. pedal at idle:



Not sure if that is acceptable noise or too much.

I'd be really confident it was a problem in the DBW circuit if it hadn't started running so poorly that one time. It's parked now and I'm driving a different vehicle until I get a chance to work on it some more next weekend.

[Steve108]

Well I think I found the problem. Anyone seen this before?



Now the question is why?

1. Agressive cleaning by a previous owner?
2. Normal wear? (car has ~130K mi)
3. Poor calibration causes motor to force it at idle?

The other question is do I need a special tool to calibrate a replacement with the computer? I am seeing mixed info on this.

If I do need a special tool, I think I'll just put a new gear in my old TB, which should work unless the calibration caused the gear to fail in the first place.

[Steve108]

I bought a throttle body off of a wrecked 2010 w/ about 44K, swapped the gear in to my TB and put it back on the car. Cleared codes and it is running great again, no more errors.

The gear from the 2010 showed a tiny bit of wear, so I put it in 180 degrees off of how it had been to give the idle part of the gear a little break, since that's where the wear seems to occur. The wear was so minor that I don't really believe it is 1/3 the wear of mine, although it probably happens exponentially rather than linearly.

Still curious if anyone has insight on this possibly being a calibration issue vs. normal wear or damage from mishandling.

[BRAIDusa]

Great work Steve.