Could pbx cause cruise error?

BAMxi · 06-09-2011, 09:34 AM

So, I've had a few separate occasions where, when attempting to set the cruise control on the highway, I got the orange "cruise control malfunction" error with the "!" next to it. If the car is turned off and restarted, the cruise will work correctly, often for long periods of time. These other times I received the error seem to have nothing in common (different roads, speed, time of day, length of trip, and amount of time car had been sitting). I took it to the dealer to get it checked out, so I naturally turned my pbx off. They didn't find the cruise to be malfunctioning, nor any stored faults. When picking my car up, I turned the pbx back on, drove down the highway, and got the error right away. This morning, the cruise is working fine again. Now I'm trying to decide if somehow having the pbx installed could be causing the issue. The previous times I got the error, I had not messed with the pbx at all, but did have it installed. So, I don't see a strong correlation going on here at all, but I figured it was worth at least asking. What do you think?

For cliffnotes, read the title :-)

Thanks!

fdriller9 · 06-09-2011, 10:43 AM

Having you been turning DSC off? Cruise control doesn't work with it disabled.

BAMxi · 06-09-2011, 11:55 AM

Nope DSC is on. Good call, though.

fdriller9 · 06-09-2011, 12:27 PM

Hmm, I would check ABS sensors next.

e90pilot · 06-09-2011, 06:01 PM

The PBX does alter the throttle signal, but I'm not sure how. I know that the cruise control does not send information to the engine via the throttle pedal. There's a separate mode of communication there. I'm wondering where the PBX is altering the signal. If it's dealing with the throttle pedal, it really shouldn't interfere with the cruise control. Cruise control is automatically disabled if you hold the throttle down above the desired speed for too long. Maybe a spike in the throttle signal is causing the fault to occur. Check for exposed or loose wiring in the PBX connections.

BAMxi · 06-09-2011, 09:51 PM

Hmm good point. I did just have my brake pads replaced a couple months ago, so I'd imagine they would have noted any sensor issue there, but probably worth another look. You think there could be some sort of wheel speed sensor issue going on? Seems weird that it would just randomly affect the cruise and not throw any errors under normal driving, but I'm not really clear on how all these different sensors work together, either.

BAMxi · 07-08-2011, 02:33 PM

I might as well update this in case somebody else stumbles upon this post. I took it into the dealer and they diagnosed a failing DSC module. I had it replaced under warranty (on the last day of my warranty period...yikes!), but I believe it's like a $540 part. I'm still not sure if there was any correllation between the DSC module failing and the PBX, but I can't imagine the function of the PBX interfering with DSC, since they are two different systems. I did recently have my brake pads replaced, as well as the fluid flushed, in addition to previously having the transfer case servo replaced several months prior to all of that.

06-09-2011, 09:34 AM	#1
BAMxi Lieutenant 30 Rep 487 Posts Drives: E90 328xi Join Date: Aug 2010 Location: Columbia, MO iTrader: (3) Garage List 2007 328xi [10.00]	Could pbx cause cruise error? So, I've had a few separate occasions where, when attempting to set the cruise control on the highway, I got the orange "cruise control malfunction" error with the "!" next to it. If the car is turned off and restarted, the cruise will work correctly, often for long periods of time. These other times I received the error seem to have nothing in common (different roads, speed, time of day, length of trip, and amount of time car had been sitting). I took it to the dealer to get it checked out, so I naturally turned my pbx off. They didn't find the cruise to be malfunctioning, nor any stored faults. When picking my car up, I turned the pbx back on, drove down the highway, and got the error right away. This morning, the cruise is working fine again. Now I'm trying to decide if somehow having the pbx installed could be causing the issue. The previous times I got the error, I had not messed with the pbx at all, but did have it installed. So, I don't see a strong correlation going on here at all, but I figured it was worth at least asking. What do you think? For cliffnotes, read the title :-) Thanks! __________________ Eibach Pro Kit \| 19" Avant Garde M341 \| BMS PBX
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06-09-2011, 10:43 AM	#2
fdriller9 Banned 253 Rep 7,089 Posts Drives: '06 AW 330xi Join Date: Mar 2009 Location: North Jersey/Philly/NYC iTrader: (4) Garage List 2006 330xi [6.44]	Having you been turning DSC off? Cruise control doesn't work with it disabled.
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06-09-2011, 11:55 AM	#3
BAMxi Lieutenant 30 Rep 487 Posts Drives: E90 328xi Join Date: Aug 2010 Location: Columbia, MO iTrader: (3) Garage List 2007 328xi [10.00]	Nope DSC is on. Good call, though. __________________ Eibach Pro Kit \| 19" Avant Garde M341 \| BMS PBX
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06-09-2011, 12:27 PM	#4
fdriller9 Banned 253 Rep 7,089 Posts Drives: '06 AW 330xi Join Date: Mar 2009 Location: North Jersey/Philly/NYC iTrader: (4) Garage List 2006 330xi [6.44]	Hmm, I would check ABS sensors next.
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06-09-2011, 06:01 PM	#5
e90pilot Freight Dawg 104 Rep 2,103 Posts Drives: E90 325i Join Date: Jul 2005 Location: Oakland, CA iTrader: (3)	The PBX does alter the throttle signal, but I'm not sure how. I know that the cruise control does not send information to the engine via the throttle pedal. There's a separate mode of communication there. I'm wondering where the PBX is altering the signal. If it's dealing with the throttle pedal, it really shouldn't interfere with the cruise control. Cruise control is automatically disabled if you hold the throttle down above the desired speed for too long. Maybe a spike in the throttle signal is causing the fault to occur. Check for exposed or loose wiring in the PBX connections. __________________ --Marcelo '06 Arctic Metallic 325i \| Sport Package \| 6MT \| Dinan Stage III suspension \| Dinan exhaust \| 330i manifold swap! Click here! \| Active Autowerke tune \| 135i Brake Calipers \| Deiselboost caliper brackets \| E46 M3 front rotors
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06-09-2011, 09:51 PM	#6
BAMxi Lieutenant 30 Rep 487 Posts Drives: E90 328xi Join Date: Aug 2010 Location: Columbia, MO iTrader: (3) Garage List 2007 328xi [10.00]	Hmm good point. I did just have my brake pads replaced a couple months ago, so I'd imagine they would have noted any sensor issue there, but probably worth another look. You think there could be some sort of wheel speed sensor issue going on? Seems weird that it would just randomly affect the cruise and not throw any errors under normal driving, but I'm not really clear on how all these different sensors work together, either. __________________ Eibach Pro Kit \| 19" Avant Garde M341 \| BMS PBX
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07-08-2011, 02:33 PM	#7
BAMxi Lieutenant 30 Rep 487 Posts Drives: E90 328xi Join Date: Aug 2010 Location: Columbia, MO iTrader: (3) Garage List 2007 328xi [10.00]	I might as well update this in case somebody else stumbles upon this post. I took it into the dealer and they diagnosed a failing DSC module. I had it replaced under warranty (on the last day of my warranty period...yikes!), but I believe it's like a $540 part. I'm still not sure if there was any correllation between the DSC module failing and the PBX, but I can't imagine the function of the PBX interfering with DSC, since they are two different systems. I did recently have my brake pads replaced, as well as the fluid flushed, in addition to previously having the transfer case servo replaced several months prior to all of that.
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