2002 Buick Century P1635 Error Code

  • 98,000 MILES
I don't know much about cars, or the symptoms of anything faulty, so I'm hoping someone with more expertise can take all the info and give me a step in the right direction before I take it to a mechanic:

My issue started about a month ago. Basically, when I start the car, it starts fine, but when I put it in reverse it putters a little as I back out of my driveway. When I put it in drive and press on the accelerator, it starts to go but then stops moving. The car doesn't die, but just doesn't accelerate even tho my foot is pressing on the accelerator. There is no sound like revving as this happens. It happens for a couple seconds and suddenly starts going again and drives fine the rest of the ride, no hesitation of any kind after stopping at a light or anything. The problem doesn't happen every time I start the car, but I'd say a good 95% of the time. After the initial 10-15 seconds upon start up, I have no issues with hesitation or anything. When it first happened, I put some Seafoam in the gas tank when it was close to empty, changed the fuel filter, and then put some Lucas fuel system cleaner in it before my next fill up. Up until two days ago, the check engine light wasn't even on. It came on, and as soon as it did I took it to Advanced and got a P1635 code reading. Did a little research and saw that it has to do with about 4 or 5 things, which I'm sure the pros are familiar with. The light has since gone off, so now I'm not even seeing the check engine light. With the description of how my car is riding along with the error code, can anybody possibly narrow down what it is? I'd really appreciate any kind of answer. Thank you.
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Wednesday, October 9th, 2013 AT 5:28 PM

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P1635 - 5 Volt Reference Circuit

Unfortunately that code isn't very descriptive. My best guess is it is referring to a problem in the Engine Computer, or that wire is shorted to a metal part of the engine or body. That 5.0 volts is produced in and carefully regulated by the Engine Computer. It feeds many of the engine sensors like the throttle position sensor and MAP sensor. If that voltage is lost to just one sensor, a fault code will be set for that sensor. This code suggests the voltage is being lost for all of them on that circuit, and the computer recognizes that is not the fault of all of them.

When the Check Engine light turns off while you're driving, that means it was a relatively minor problem, as far as emissions is concerned, and it went away at the moment. The code will stay in memory when the light turns off. The way I would approach this is to fashion a connection to the 5.0 volt terminal on the easiest sensor to get to which is usually the throttle position sensor, then use a small jumper wire to connect that to the lead of a voltmeter so you can watch if that voltage disappears intermittently. If it does, the trick is to get it to stay that way so you have time to do some troubleshooting. Shorted sensors are rare, but in this case I would disconnect one at a time and watch to see if that 5.0 volts comes back. MAP sensors have internal circuitry that can short, although that would be rare. Throttle position sensors really can't short. You can also move wire harnesses around to see if one is rubbing on something causing a wire to ground out to the body or engine.

A mechanical problem like a wire rubbed through should really cause problems more often than just for a few seconds after starting the engine. From the way you described how little it acts up, that is more characteristic of how a sensor would act when it's in the early stages of failing.
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Thursday, October 10th, 2013 AT 2:40 AM

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