If this is how your going about getting fixed , then it may be cheaper to take it to a good shop , a good shop would only replace what tests bad , not just replace a bunch of things to see if that fixes it .
Then again because of your lack of understanding , the sensors do share the same 5v reference , but do not & can not share the same signal return .
Just a suggestion to save you money & grief .

 

John,
My wording was poor. Same 5v supply and common return. Of course seperate signal from sensor. Forgive me. I may be a lousy typist but I didn't come from under a rock.
The reality is that I would love to have access to sufficient information, i.e. detailed profesional grade manuals, to trouble shoot this problem. Would love a DRBIII scanner too for that matter. But the truth is I live in BFE. Closest good shop is >90miles in Buffalo NY.
Local dealer is 20 miles. $80/hr minimum 2 hours labor charge just to hook up. Not fixing anything. Their words were, "Your truck is not stock and our policy is not to service them". He then introduced me to the salesman for a new truck.

Have to tow it to either shop.

Dealer would only give me resistances and a couple of voltages. Books that have "not common" information >$400 per.

Cost of the sensors less than any of the other options. I assume risk that problem isn't solved. Problem is apparently intermittent with only consistant error being TPPS. MAP sensor reads approximatley twice what std pressure should be.

Sorry to flame on as I really do appreciate your help. Truth be known if there was someone local to fix it they would be hired in an instant, I really don't have the time.

 

There was no insult in tended , but it is common that when replying to statements that read like someone is just throwing parts at a problem & no diagnostic attempts [ just like the dealers do ] that I come down harsh on that type of work , its just a matter of factual response , with no intent , if you were a dealer tech , I would PM you , and use all kind of unusable language .
So lets start again , how familiar are you with basic electronics & do you have a good multimeter [ low impedance , digital , hopefully a bar graph ] ?
I've have had all of the pro tools & sources of info , still have some of that .
And with about 30 yrs. of experience now , I can [ many times , but not all ] get by with minimal equipment .
To start , doing a resistance test on the sensors , then doing what ever makes them react , heat on a temp , movement on a TPS or crank , what you want to see on the active side of any sensor , is a steady reaction to , heat/movement , with no glitches [ this is best done with a scope , but a good multimeter may find the really bad glitches ] .
Be watchful of connectors when disconnecting / reconnecting that they are clean & snug on the metal connections , in most all cases I like to use a spray connector cleaner [ plastic safe ] then put back together with a dab of dielectric grease .
Then back probing at the computer any suspected circuits , in for no other reason , to make sure that a good signal is getting through harness to computer .
This is the main reason that dealers throw parts at a problem , it is very tedious/time consuming & takes a good detailed knowledge of basic electronics to chase down just what is wrong , then replace only that .
The dealers make more profit by not having [ paying for ] really good techs , then selling more parts , witch is where my ***** is .

 

yes those do read barometeric pressure when engine is off and running, more than likely your apps is causing the 5 volt supply to be shorted causing the rest of the sensors on that 5v ref. do go dead, those oil press. senders go bad all the time to. as far as your map/boost sensor, to get a true boost reading from it you must take the key on engine off reading and subtract it from the highest pressure reading you get under load, this will be the amount of boost the ecm is being told it is building P0121-ACCEL POS SENSOR VOLTS DO NOT AGREE W/IDLE VALID
SIGN P0122-APP SENSOR SIGNAL VOLTAGE
When Monitored: During engine running operation.
Set Condition: Low voltage detected at APPS signal circuit or low voltage detected
between the Engine Control Module (ECM) and the Power Train Control Module (PCM). hope these help, did a little research on the p0123 could find nothing for this dtc

 

P0123 Apps signal voltage too high. Apps voltage input above max acceptable voltage. this along with the other codes, I would inspect the wires going to the various sensors, I suspect that one is rubbing and shorting to ground, making the supply voltage jump around. Either that or a bad MAP sensor shorting.

 

Scott: My truck does the same thing now and then. With my truck it is the Edge Comp. I see you live where it is cold, the Comps hate the cold weather.

Try removing the Comp and see how it runs. When I start my truck in the morning I have to cycle the key a few times just to get the thing to turn on.

Also on the Comp wire harness where it plugs into the back of the unit there is a resistor under the shrink wrap by the connector. If the harness has been bent or twisted it may have damaged the resistor.

 

John, no offense taken. I have a strong background, (not professional) in electronics and electrical theory. I have most of the toys including a scope. I can't find the probes for the latter.
I did see a glitch in the output of the apps with the graphing function of my obdII scanner, .i.e. the signal dropped as I moved the sensor from 0 to 100%.
I also monitored the 5v source voltage. My DVM read a very solid 5.02v, the bar graph did not show any fluctuations. Replaced the apps sensor and set voltage. Glitch is gone, but truck still isn't right. Similar problem, except the the duration of the event is short but at a higher frequency. Before when it was dead it was dead, now it only lasts a split second.

My edge comp has been disconnected and removed. I thought the same thing unfortunatley it made no difference.

When I remove the MAP sensor connector the computer defaults to 29.37"Hg. With it plugged in it reads 56" idle and will respond to turbo spin up. You can see the turbo lag if you hit the throttle quickly. I have not as of yet done a quantitative test but qualitativley it responds, just with a wrong value.

I did check the sensor return (not signal return) and found that it floats 15mV higher than ground. It does seem to jump around a bit when it acts up. abit means floating from 15mV to about 40mV. I checked this at the MAP sensor connection. I have not checked at the ECM pin out yet. It is raining/snowing/blowing right now and the last thing I want to do is short something out. For today it was easier to pick up the sensor return at the MAP connection. I did find that the return has an AC compontent of 35 to 50mV. Frequency depends on RPM (100 to 900Hz). Need to get my scope out as the dvm isn't that great outside of a couple hundred Hz.
FYI new tpps will throw the low voltage code when it acts up. But I can clear it now and it will stay clear until it acts up again.

I have not tested my oil pressure sensor yet nor the cam position sensor, other than checking the wires and connections. WIll do that when the weather gets better.
Here is a rundown of what I know so far in regard to the sensors:

1) Coolant Sensor, responds accuratley and output not effected with problem
2) IAT Sensor. Same as coolant, accurate and not effected.
3) Oil Pressure sensor, appears accurate until it acts up and then drops to zero.
4) MAPS. Providing output twice actual. When acting up goes to 75"hg.
5) APPS. Responds smoothly at output of sensor. I see no variation in output when engine is acting up, although ECM thinks it has a low voltage.
6) CAM Sensor. Unknown. Tach is stable and appears to respond properly to RPM without obvious fluctuations even when the engine acts up. It is a new sensor when I rebuilt the motor last year. I do have the one that I replaced and it was working when I changed it. (It was easy to get to with VP out and the engine on a stand)

The sensors being effected when the engine acts up are the oil pressure and MAP sensor. I don't know what the output of the cam sensor is. I would assume that is doesn't have the circuitry in it to convert pulse to voltage so will need my scope to see it. If anyone knows let me know.

I am also interested in what the correct reading for the MAPS should be.

When I get a break in the weather, I will double check the connections and pins/sockets on the ECM. I am will also check between the sensor return and battery return on the plug for any voltage drop. I also plan on unbundling the wire harness and checking the wires. Yes I will rebudle them in spiral wrap when I am done. ;-)

Thanks, I REALLY do appreciate the help and knowledge being offered.

 

PO123 (M) =TPS Voltage High, TPS/APPS input voltage above the maximum acceptable voltage
If your oil pressure sending unit is bad, and sends a 0 psi reading to the ECM, the ECM then sends a defuel (limp home reduced power mode) command to the PCM.
The same defuel command applies when the MAP/Superboost sensor fails.

 

It sounds like your going about this in a good way , but these problems can be tedious to run down .
Weather , where is this globule warming they keep telling us about , keeping me from doing stuff also .
You need to isolate the offending sensor's , one at a time to see if one is the cause , vs reacting to symptom .
I bought a tool some time back [ there are about 3 levels of these to do most ] that will put out a number sensor readings , volts , resistance , pulse , ect. , that I have use to put a good signal to a suspected circuit , to verify whats / what .
Many times a problem like this is where the dealer way of fixing things can work , but cost too much - throwing parts at the problem till it goes away .

 

Global warming hasn't hit here. We are suppose to have 12" of snow by wednesday. Just another way to tax us.

Sun is out today. Will update as I get into it today.

 

E-mail or call this guy Timbom1976@aol.com, 717-577-1464.

Ask him to send you an accelerator pedal position sensor, he will e-mail an invoice for pay-pal for a less expensive alternative than the dealer.

You will have it in 2-3 days, install it and enjoy your truck again.

The other codes are caused by the bad sensor, I don't know why.

My cts readings were all over place and seemed to follow the tps reading, and the map code is caused by the comp.

I just went through all this a month ago.

I was going to try to find out why the other readings were messed up, but after installing a new apps and seeing how much better the truck runs, I just don't care.

 

Just put Tim's sensor in a couple of days ago. Corrected my dead spot but did not correct other. Still have problem.
Did find a marginal plug on cam position sensor. cleaning that now. looking up what size allen fits the bolt.
Want to look at the sensor closer and check the pins.

 

it is a 4 mm allen socket

 

Thanks. With the help of my 11yr old Pulled sensor. Found nothing major wrong other than retainer tab was broken. Put my spare in non the less. As expected no difference. Checked cables back to ECM no shorts or opens.

On to the next circuit. Trying to get tool around MAPS sensor to test that, same with oil pressure sensor.

 

Ttesting wire by wire is tedious. I am finding that in order to visually inspect the wires almost need to pull the wiring harness out. Difficult to see and hard to get to when under the hood. This will take a while but it is a good excuse to be outside today.