Engine/Transmission (1998.5 - 2002) Ecm/pcm issue?

[Kf6cmp]

I have a problome with my Truck. I keep getting a check engine light p121. Now I know this has to to with the throttle position sensor . So I reset the trouble code i. e. cleared it. It came back on again. So I went to recalibrate it. Disconected my ground on the batteries and let it sit for a few hours. Then reconected the Batteries and turned key on and did the three slow applications of accelerater peddle. It reset. Now my wait to start light isnt working and after a few hours of driving, my truck threw another code. yep, p121. On the way home from work my speedometer started jumping around and finally just fell to zero. The truck seems to be running fine. After reading a few hours on forums, it seems that the Ecm/pcm could be the issue. Does this seem plossible? I had a simular issue a few months back. My wait to start light stopped working and a few weeks later my starter failed, Cheap Napa starter, and after replacing starter and reconecting my batteries, a day or so of disconect, my wait to start light worked again.

 

[Sticks]

All the lights in the dash should com on for a second or two every time you go from off to run.

It might be that your gauge assembly has gone TU. ECM and PCM are fine, just the gauge cluster is toast. Not sure if there is a way to test. Some generic code scanners will show VSS (vehicle speed sensor) output. The one that I got from Harbor Freight does, so I can be connected to the OBDII port and see if I am getting VSS output. If it's working and dash shows nothing, safe bet that it (gauge cluster) needs replaced. If you have a buddy with the same year/model vehicle, you may be able to swap out and verify. Might tweak the actual mileage, so don't do it for more than testing... like long enough to see that the speedo works.

At least you are getting the TPS code. I had no codes, just symptoms then it up and died at a stoplight before it threw a code. Get it changed out. Do a search on here. There is a procedure for using a different TPS module and adapter rather than spending the HUGE $$$ the dealers want for the whole assembly.

 

[ph]

Hey Kf6cmp,

There are some excellent diagnostions on this site and I consider Sticks to be one. On my truck though, I solved several "intermittant", and/or varying symptoms by cleaning and re-assembling with dialectric grease all of the grounds that I could locate. It's by far the most economical place to start. I'm 100% with sticks on the TPS as the next step. Hope this is of some help.
ph

 

[Kf6cmp]

Well thanks ,ph and sticks. I just went through the grounds ,about 6 of them, and they are tight and look good. So next I will replace the tps. I need to order one through Geno's. I know that part is bad, and maybe the other symtoms will go away with the part replaced. Chris

 

[Kf6cmp]

Does anyone know if the aps from Geno's is any good?

 

[JR]

I bought one through them last year. It seems to be of good quality, no issues to date. Just follow the instructions for calibration and you will be fine

 

[Kf6cmp]

Thanks, just ordered it.

 

[Kf6cmp]

So, I did the APPS reset and the truck started up and I drove it around the block with none tps code being thrown. Also speedo is working now. When I started the truck the wait to start light worked. But when getting back to house and shutting down and restarting the light didnt work. I tried pushing on cluster and it worked. Maybe cluster conection is dirty or just a huge coincidence! I will put new tps in and hope this takes care of the issue. I will pull the istrument cluster and clean contacts and replace , also.

 

[Sticks]

Likely you have two unrelated issues going on.

Checking the grounds for tight is not enough. You pretty much need to pull, clean (scotchbrite or 250 grit sandpaper) then reinstall.

Good idea on pulling your gauge cluster connections and cleaning them. This many years, dust, humidity and vibration starts to take it's toll. That might be the source of your issues there.

Keep an eye on the TPS. Hopefully the cleaning the grounds was enough to solve that issue, but in my experience, once they start to go, they are gone (design flaw).

 

[Gary - K7GLD]

Likely you have two unrelated issues going on.



Checking the grounds for tight is not enough. You pretty much need to pull, clean (scotchbrite or 250 grit sandpaper) then reinstall.



Good idea on pulling your gauge cluster connections and cleaning them. This many years, dust, humidity and vibration starts to take it's toll. That might be the source of your issues there.



Keep an eye on the TPS. Hopefully the cleaning the grounds was enough to solve that issue, but in my experience, once they start to go, they are gone (design flaw).

All that, plus, crimped-on end connectors are the pits! Hidden corrosion and resulting deteriorated conductivity result in lots of "mystery" symptoms and failures. MANY sensors in later computer controlled vehicles use very low voltages and signal levels - and resulting loss of connector conductivity can sideline a vehicle as easily as a blown engine or transmission...



As much as possible, I prefer to actually solder connections for best and long-term reliability...