About three months ago, while driving down the highway, I hammered the go pedal to haul out from a yuppie tailgaiting me. At about 2300 RPM, bam nothing, like I shut the engine off with the key... I got off the pedal, and it was idling fine. Rev the engine, a few times with no problem. So I head on my way, although the check engine light is on. Ran fine with no trouble for weeks, and the code cleared itself. Then it happened again, and would do so a few times a week now.

So I went to autozone and used the scanner. P1689, no communication between injection pump and ECM. So I took off the EZ, and the TST and double checked all the wires. Still had the problem a few times a week, but only above 2000 RPM, and with pretty decent pedal depressed.

Now, it really died. I had to drive home essentially idling in 6th gear at 30 MPH (gotta love that low end torque..). It was idling perfectly and running very well loaded in 6th gear idling, putting out some smoke, and generally pulling perfectly. So I was really thinking it could be the APPS and got the idea to try the cruise control. I had to wait till I was going down a hill and hit 35 MPH, then set the cruise control, and it worked fine !! I could use the accelerate button on the cruise and she ran great any speed, any load. But the pedal was still dead.....

This really screams APPS, but the code it threw is unrelated to the APPS and many people say the P1689 is a VP death code???? But it runs postively perfectly on cruise control

Anybody have any ideas???

 

If it works perfectly on the CC, then that all but guarantees that it's the APPS in my mind.

Good to see you on here, Kev--

 

How is the CC any different than using your foot on the pedal? (on a 6.5 chev when the CCis used it controls veh speed via the ecm not the apps) I'll go look at my truck, maybe I'm missing something but I'm sure mine has a cable from the apps to a throttle actuator.

Midwest fuel injection lists the 1698 code as a usual suspect for a bad pump, but they also say there are some electrical checks that should be done as well

 

The APPS is still used on cruise in these trucks. A vaccum solenoid just tugs on it instead of your right foot when the CC is activated. The 1689 is typically a failure of the VP44 ECU board. You know how it goes....starts out random and intermitent but only gets worse from there. I have never heard of a 1689 meaning anything other than VP44 replacement. No BUS COMM means that the VP44 ECU stopped talking to the ECM. I suppose you could double check the connectors for continuity but this does sound like a classic PC board failure.

 

Thanks for the replies!!

No, the CC on the truck does not operate the APPS with a vacuum pot or anything. It is straight drive by wire from the ECM or PCM. Only thing that moves the APPS is the go pedal.


I agree with you Hohn, the CC test seems to confirm to me nearly certainly, its the APPS.

Doing the key on-off trick, I found last night also 0121 code, which is indeed the APPS, so I feel pretty good about changing that out.

I think I might have thrown the 1689 code, when I took off the EZ or TST while troubleshooting. I might have momentarily created a bus fault and threw the code.

 

What year did that change? No cruise solenoid under the drivers side battery?

Yup, the 0121 certainly confirms APPS. Hopefully, the 1689 was a fluke.

 

I know '01 and '02 trucks have electronic cruise. Change was made in either '99 or '00.

 

Kev, I don't know if you found a cheap replacement, but my shopping
showed Hoesli's as having the best price.

 

It looks like several major ECM BUS changes occured for the 01 model year. I'm betting the APPS control and electronic CC were included in that. Everything on the 98.5 - 00 appears identical.

 

not to hijack, but I just got the pcm 1693 and ecu 121 fault today also on my way to work, happend trying to merge into traffic from an on ramp, not a good place to loose your throttle. cycled key and was running fine again.

DuaneW.