On Wed, Apr 20, 2011 at 11:30 AM, john niolon <jniolon@bham.rr.com> wrote:
> My 2003 Tahoe takes me to the shop when I am away from it (shop content).
> Road trip down I-65 this weekend and three times my check engine light
comes
> on... dash display says "reduced engine power" and it drops to 4
cylinders...
> coasted to shoulder, turned it off...sit a minute and restarted ...all
ok...
>
> diagnostic code on return shows P1516... B google found some info on a
broken
> wire (inside the insulation) on the Throttle Body B or a bad crimp on the
TB
> wiring connections...
>
> any one else ever have this problem..
>
> on several occasions in the past I've had this same problem (check engine
> light and reduced power) when first starting (either cold or hot) and it
went
> away with a restart... B related ??
>
P1516 is a GM specific code (the P means "powertrain", the 1 means
manufacturer specifc, 5 means vehicle speed, throttle, and idle
control). This particular code means the throttle acuator control --
which is the thing that actually moves the blade in the throttle body
-- doesn't know what the position is, or the position isn't what it
should be. There was a TSB about the wiring being defective (which is
probably what you found). Other causes are the sensor at the gas
pedal is wrong, the throttle body is stuck or otherwise not moving
right (there's a motor), or the throttle position sensors are screwy.
If I remember right, there are a bunch of different reduced power
modes available. One forces the engine to shut off, which isn't
what's happened. The others force idle only, reduce acceleration
(limits the rate at which revs can increase), or limit the max
throttle opening.
You can inspect the wiring, and check that your throttle body isn't
stuck or covered in carbon. After that, you'll need diagnostic
equipment. There are a pair of throttle positioning sensors in the
throttle body that you can check produce the right signals as the
throttle is positioned, and the sensor at the accelerator pedal (Oh,
probably not your problem, but don't touch the gas pedal when
starting. It doesn't do any good, but one of the things the computer
learns is closed throttle position. If it isn't closed, it's
unhappy.) ditto. A scan tool can tell you the values reported, you
can also check them with a 'scope, but I have no idea what they're
supposed to be.
--
David Scheidt
dmscheidt@gmail.com
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