Hi, I have a 2000 f250 psd 7.3 4x4 lariat, with a 'service engine soon' when pedal pressed error, fuses are ok. A while back I replaced my batteries and noticed the glow plug relay wasn't working (should have checked before buying two new batteries). After I swapped it out I noticed the lack of throttle response after startup and the SES light. I would idle it and it would disappear. I drove it like this for about a month at which point the SES light came on for good when pedal pressed. The truck is stuck at a buddies now, and I've been over to work on it as often as I can, but would like to fix it soon.

When I pulled the codes on it (FORscan & 327 elm), I had; p0122,p0123,p0221,p0478,p0470
I replaced the pedal from the local pick-a-part. And took a look at the EBP, which was too fused on to remove, so I poked a wire down the tube about halfway as it was so backed up. I'm ignoring that for now as I can fix that once I have my truck back home. This has reduced my errors to only p0221 and p0478 with a SES light and no throttle still.

I followed this AP/IVS Pedal Position Sensor/Idle Validation Switch page (APS=123 AVS=AB)
Connector Checks to Ground
2 and 3 to Grd are questionable (my tester is a cheap china knockoff)
Connector Voltage Checks
ok
Harness Resistance Checks
open! 91-1
ok-89-2
ok-90-3
Operational Voltage Checks
ok-Range is good and responds to throttle (.55v-3.69v)

So from that I gathered that there is a problem somewhere for the APS circuit between the PCM and pedal. From that page, there was a '76-way Bulkhead connector. I looked around I'm guessing it was the 42-way under the air intake on the drivers side. on my year of truck.
Testing continuity from the PCM to the 42way
ok-90-21
ok-91-19
ok-10-A
Testing continuity from the Harness to the connectors
open-21-3
open-19-1

At this point I have reached the limit of my knowledge of what to do. I guess I am looking for the #1 open/grounded wire between pedal and harness, which is as good as a needle in a haystack to me. However FORscan does show correct voltage range and if the circuit was open/grounded wouldn't it be inopperable?

What should I do next?
Anyone have circuit 359 or 351 diagrams?
Should I signup for AlldataDIY/anyone have experience with this?

Thanks for any help!

 

What year is your Truck?

 

Can't believe I missed that, it's a year 2000!

 

 

 

Thanks so much whitetmw! I'll post back with hopefully good results :-)

 

Not so great results, the IVS circuit is open. I tried jiggling the connector while I read off the IVS idle data on FORscan and eventually got it to oscillate. I thought it was the connector so I clipped it and cross-wired it, no luck. I then lost all oscillation on the circuit and no amount of wiggling and jiggling could get the idle off.

Is it possible to wire the idle off at an earlier point in the circuit and if so are there any side effects?

 

I got the ivs mostly off idle so this allowed me to drive home; by finding a loose splice located directly above the pedal. If I jiggle it just right I got it to stay 'off idle'. On the way there my ride was rough and i had intermittent power. at times complete loss of power and idle only (ses). I pegged in my cruise control and that evened it out; smooth driving.

Now that it is home, I am onto dismantling dash and replacing/resplicing the wiring harness.

 

Glad your making good progress. Was it a factory splice or a previous repair?

 

Factory splice.

 

Update, a possible good news turns bad. After some very conflicting results I think that it's my PCM.

Originally, I was receiving a good connection to PIN 10 for the vref BUT fluctuating Power, from 4-11v, then I was able to jiggle the harness and get a steady voltage and get the IVS to operate enough to get home. Once home and dismantled my dash, and I got into the harness/slice power oscillations halted and were a steady 11v. However I can no longer get the IVS to 'off idle', connection is good to pin 10 still. I even checked using a breakout fuse from another 10a circuit to the VREF and it wouldn't leave idle. IVS vref to ground is not present (testing to ground on brake connector)

So for tom's IVS diagnostic;
FE2 No
FE3 No
FE4 Yes
FE5 Yes
FE6 Yes
FE7 Replaced pedal to no avail

Before I buy a PCM, is there any chance that my OTC light is out is related? Or that my ignition was popped (currently using a screwdriver)? Or perhaps PCM Pin 10 is seating with the harness?

Is it common for a PCM to fail ONLY on one circuit? From the video's I've been youtubin; the PCM looks like it went in a smoker for 2 hours.

 

After looking into replacing a PCM and the pita it would be to get one, I took another look at the vref circuit. I was able to get the IVS off idle, but wasn't able to get it to reliably go on/off. So looks like the PCM is 'ok'... sigh

I'm starting to get pretty anoyed, and my wife wants to sell...

Any reason to not clip the VREF pin 10 at the harness and rerun a wire, just to rule out a vref?

 

Put a T-tap splice onto the vref right out of the harness to the PCM. Still no getting it off idle.

 

"T-Pin" (Back probe) the signal wire and see if your seeing a signal to the PCM from the Pedal. If you see a signal, the PCM is most probably the culprit. DVOM set to Hz or Use A Scope. DO NOT ALLOW THE "T-PIN" TO TOUCH SYSTEM VOLTAGE! Or, you will be buying a new PCM.

If you see signal, check again at the PCM. Again, DO NOT ALLOW THE "T-PIN" TO TOUCH SYSTEM VOLTAGE!

Be CAREFUL with this test!

Raise the rear USE JACK STANDS!, BLOCK THE FRONT WHEELS and see if you can get it to 26 MPH, Set Cruise Control and see if it maintains, accelerates using the Cruise Switches. This will eliminate the PCM.

DO NOT SLAM THE BRAKES ON! You could damage an ABS Sensor.

Do you have access to a Bi-Directional Scan Tool to monitor PID's?

You may also have an ABS or Speed Sensor DTC Set as a result.

 

Hi Tom,

I was able to get some time on the truck, I looked up a t-pin; works great! WAY better than splicing in. The things you learn! I was able to get a reading and I can see a signal going to the PCM.

I wasn't brave enough to test the Jack stands, though when I did get it home, cruise control evened out the ride. (I think it was switching idle/off idle from p0221 / IVS).

Will start to look for a PCM on Monday. - Thanks again.