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Old 12-13-2012, 03:02 PM   #1 (permalink)
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Accelerator Pedal Position Sensor

Good Afternoon. Need some help with a 2002 GMC Savana 3500 with an F-code 6.5. Over the past several months i've experienced some intermittent problems with the cruise control. It will set at a speed OK, but sometimes will lose the set point if i use the accelerator manually to pass traffic or it will not resume speed from the R/A switch after a brake application. The problem is more frequently seen after manual use of the accelerator. This morning, i experienced a "no response" accelerator pedal several times when attempting to accelerate away from a stop. That is, step on the pedal, and no response from the engine. Once, i just went deeper and the engine roared abruptly to life, mostly i let up and tried again, and the engine responded to the pedal normally. I am leaning toward a bad APP Sensor, but as of yet have not put meters to it to test. My repair manual says replacing the APP Sensor requires a proprietary factory tool to calibrate a replacement. The part is salty enough ($400ish) at my NAPA, if i must have the dealer calibrate it, obviously they will not use my part. I see this as an expensive bill if the dealer has to be involved. Does anyone know if replacing this part is just plug and play, or does it require a calibration of some kind? Thanks for any help, in advance.

Last edited by jjp; 12-13-2012 at 03:03 PM.
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Old 12-13-2012, 03:09 PM   #2 (permalink)
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The APPS is the whole throttle pedal assembly and doesn't require any calibration. If you replaced just the actual sensor calibration would be required, but I don't know of any place to buy just the APPS sensor. Has your service throttle light ever came on? The APPS rarely fails as it is a 3 sided triple redundant assembly. Even if 1 goes out, it will still run completely normal on the other 2, and if 2 goes out it will run in limp mode on 1. Check with the dealer as I bought one for mine 3 years ago for about $270 from them(put it in when I did my DMAX swap even though my old one was still good).

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Old 12-13-2012, 07:00 PM   #3 (permalink)
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No codes or service throttle lights at all. Just the intermittent problem with the cruise control for several months now, and the loss of any response to the pedal four or five times this morning. The van had sat unused for about twelve days until this morning, and the non responding pedal problem went away the longer i drove. Outside air temps were in the high 20'sF. The PMD is a Heath, on the bumper, new in June 2010, with perhaps 25,000 miles on the vehicle since installation. For now, i'm willing to discount the PMD as the cause. I keep coming back to the loss of the cruise control "set point", as if the cruise switch had been switched off, at times when i'd manually accelerate as the crucial clue. When this happens, there is nothing else involved except my foot on the pedal. This is what makes me suspect the APP Sensor. The repair manual i have talks about replacement requiring "checks of the throttle opening and throttle closing ranges with a proprietary factory scan tool". This, obviously, i can't do, and do not really want to pay any of the local GM service departments to do either. But i do understand your point about the replacement being a whole assembly, the part i was shown includes the whole pedal. I can't really see anything to calibrate or check. If time permits tommorow i'm gong to measure some voltages as described in the FAQ's. I have another car that has become a parts hanging exercise, i'd like to avoid another, especially with $300-$400 parts.
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Old 12-13-2012, 07:18 PM   #4 (permalink)
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Since the diesel does not have a throttle to set opening and closing points of any kind and is drive by wire technology,I would say that your service manual is referring to a gas engine service procedure.
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Old 12-13-2012, 07:56 PM   #5 (permalink)
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Before suspecting the APP without any DTC to support it I'd suspect the cruise control is malfunctioning. If not the firewall unit then the multifunction switch module in the steering column. Pull the fuse and drive without the CC for a week and see if there are any throttle abnormalities. If not, I'd say the CC is your problem. ~FH

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Old 12-13-2012, 11:59 PM   #6 (permalink)
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Cruise control problems are a classic sign of early PMD failure, so check it off the list just yet. Also a failing optic sensor or cloudy fuel can cause all of your problems. Make sure you're getting fuel pressure to the injection pump, and get a scanner on it. The chances of all 3 sides of the APPS failing together are SLIGHT to say the least.
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Old 12-14-2012, 10:31 PM   #7 (permalink)
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if your brake switch is slightly out of adjustment or going out your cruise will act up as well
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Old 12-14-2012, 11:13 PM   #8 (permalink)
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The brake switches have several contacts and if its like my 96 the switch moves with the pedal so the wires have to flex and will eventually break.
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Old 12-15-2012, 11:55 AM   #9 (permalink)
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Had the exact same problem as you. No throttle response sometimes when cold. Seemed Ok after the heater got warm. Finally one morning throttle would not work at all. Just had idle and it finally set the service throttle light. Shut off the truck, restarted and things worked ok til I got home. Got a new APP from NAPA. it was about the cheapest I could find, they gave it to me at the jobber rate. Easy to replace. Do not have to recalibrate its plug and play. Runs fine now.
APP can and do go out. Many threads here on them. Mine only had 63,000 miles on it when it went bad. And yes an erratic signal from the APP can effect the CC.
If 400 is high price. I see them used on Ebay for cheaper.
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Last edited by Tommygunner; 12-15-2012 at 12:13 PM.
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