Clay L wrote:
There are two components in the throttle position sensor system. One is the accelerator pedal assembly and the other is a black box above it on a bracket.
Since my shop admitted that they had no way of knowing which was at fault I replaced both. That took care of it - code P1516 as I recall.
Then several years later I got roughly the same symptoms but a different code - P1518. This time when the problem started (on a trip from CO to NH and back) it would reoccur on a random basis. Sometimes days apart and once twice in one day. When we got back to CO I replaced the throttle plate assembly that has a motor that moves the throttle plate. It sits on top of the throttle body injector assembly.
That was about 2600 miles ago and so far so good.
In addition to replacing the parts mentioned above I also checked all grounds involved (there are two on the top of the engine), and unplugged and replugged all connectors involved. So either that or the replacement parts fixed the problems. Since the problem was intermittent and would not show up for many miles it was not possible to do one thing and then see if it worked or not.
Having the engine go into reduced power (1st code) or idle mode (2nd code) was dangerous. I could be stopped in a traffic lane unable to get over to a breakdown lane and that is scary to me. In many places we go there wasn't a breakdown lane or even a shoulder to speak of anyway.
Because of that I threw parts at the problems - something I don't ordinarily do.
My total parts cost was close to $1000 as I recall - I did the replacement myself so no labor was involved.
In that year, is their not also a Crankshaft Position Sensor? The symptom sure seems to fit a not failing CPS... But, I'm not up on what I assume is the 8.1GM sitting in that Workhorse...
Best of luck, and OP - please close the loop back and let us not what root cause of the problem was...
Smitty
