P0123 TPS High & C0322 - will not clear - 1996 Ram CTD 47RE

[JHZR2]

I’m creating a new thread because this is more related to OBD. I had asked before about my 47RE searching under light throttle, 45-60 MPH. It’s very random. I can be driving long distances at these speeds and encounter no TC lock/unlock, or I can have it happen continuously, even if I force the transmission to turn OD off.

Ram 47RE TC searching

About the only questionable thing about my Ram is that the AT sometimes gets confused at around 45-60 mph with light throttle. The AT was replaced about 10k miles ago. No other records of prior AT replacement. I liked the idea @ram_man had to post a video of shifting behavior. This is one...

bobistheoilguy.com

So I got my hands on a scan tool, wanting to take a look at live data... The truck does not have any CELs, and shifts very well, except when it’s doing this funny business. AC ripple and/or EMI from the alternator to grounds is suspected as a culprit. I have a little battery/alternator tester, which checked out fine (and I subsequently had Autozone verify too).

I found that the truck has a P0123 and C0322. The P0123 is a generic TPS sensor high reading, the C0322 is apparently a Chrysler specific variant. Note here that I have tested my TPS at idle and WOT, and the readings are correct (1.0V and 3.8V). I pulled the TPS too, and it looks brand new. Also have cleaned the alternator and other body/engine grounds. All are bright metal.

My understanding is that the code is set if over 4.94v is seen for over 0.48s. Ive not seen this, at least not with a multimeter (scope would obviously be better).

I then took live data. The OBD reading in this tool indicates that the tps is at 20% at idle. When the pedal is floored, it never goes above about 76%. Thing is, neither of these create the high voltage required to throw the CEL

I have cleared the codes multiple times, including with the engine off, power on, and engine running. The code is never pending, and is always set even as soon as I check it again. The CEL works, but is not illuminated.

There does seem to be electric noise. The live data goes from smooth to spiky/variable, when this TC unlock and/or downshift out of OD occurs. Does this point to a short? Ive probed at the tps connector, notionally it should be the same as at the pcm connector. Is there a good way to probe the PCM connector without hacking up harnesses?

Here is a single event:

And here are examples when it searches more:

Whats the best way to get this to clear once and for all? If I disconnect the TPS altogether, and still get this code, does thst indicate a bad wire, or a bad PCM? Is it possible to remove one single wire from a 32-pin PCM harness, without messing the whole thing up?

Thanks!

 

[OVERKILL]

Are you able to sub-in another TPS? That'd be where I'd start, see if it follows the TPS or not.

 

[mk378]

See if live data works with the engine not running. Key on engine not running, move the throttle slowly over the whole range and watch the live reading. If it jumps around, the TPS is likely bad, though it could also be a bad connection on the way to the PCM.

 

[JHZR2]

See if live data works with the engine not running. Key on engine not running, move the throttle slowly over the whole range and watch the live reading. If it jumps around, the TPS is likely bad, though it could also be a bad connection on the way to the PCM.

Yes I did that and it is smooth, no issues I can observe. I tried wiggling everything when it was in that condition, and there was no issue - at most, wiggling things and knocking things created a 1% change.

Are you able to sub-in another TPS? That'd be where I'd start, see if it follows the TPS or not.

I have one coming in to NAPA today. I’m going to do just that. I had ordered it and was on the fence regarding throwing a $120+ part at it, but it’s probably worth it....

The issue is that I know the output from the TPS is a good voltage range, and is NOT high. So it can’t be shorted inside there or anything like that.

 

[wpod]

Are you thinking alternator? Could you disconnect all the wires being careful with the battery wire , insulate them and tie them out of the way and go for a drive maybe ,,, just a wild guess.

 

[JHZR2]

Are you thinking alternator? Could you disconnect all the wires being careful with the battery wire , insulate them and tie them out of the way and go for a drive maybe ,,, just a wild guess.

I was, which is why I was testing it multiple times. It always passes.

Are you able to sub-in another TPS? That'd be where I'd start, see if it follows the TPS or not.

I installed the TPS. Exactly the same result and reading. The range is 1.0-3.8V when it is installed.

Curious to me, when I have no TPS installed at all, the signal wire back to the PCM reads 5V. I don’t know if this is normal or not.

See if live data works with the engine not running. Key on engine not running, move the throttle slowly over the whole range and watch the live reading. If it jumps around, the TPS is likely bad, though it could also be a bad connection on the way to the PCM.

So, I did some more investigating in this spirit, with the old and new TPS. I am able to clear the codes with the key on, and they will seemingly stay off.

So with engine on, the codes won’t clear, but with engine off, power on, the codes will clear.

It started pouring, holding me up a bit from testing more. I will try to get a test drive with the new TPS.

 

[JHZR2]

Well it seems that Ockham’s Razor is good advice. While the old TPS checks out fine and the live data never showed anything abnormal to throw the code, something was still wrong with it.

The old and new tested the same way with a meter and live OBD data.

But the new one allowed the code to not be set again. And driving it seems to be as is correct operation. Fine shift points, no searching, all good.

The live data is generally smoother.

And no codes!

 

[clinebarger]

Curious to me, when I have no TPS installed at all, the signal wire back to the PCM reads 5V. I don’t know if this is normal or not.

That's a 5 volt resisted bias.....Those high spikes you saw in the TPS voltage could have been Opens in the potentiometer which will spike to 5 volts.

Diagrams used to include such details.....

 

[JHZR2]

That's a 5 volt resisted bias.....Those high spikes you saw in the TPS voltage could have been Opens in the potentiometer which will spike to 5 volts.

Diagrams used to include such details.....

I had a look. I’m not a whiz with wiring diagrams... but Im not sure if can make it out from this?

 

[clinebarger]

That diagram doesn't show the 5 volt supply & Resistor detail inside the PCM.....Even though it's obviously there because you get 5 volts with an open TP Signal Circuit.

The diagram I posted is of a 1995 Chevy Truck as an example of how cell diagrams should be drawn.....It even shows the .450 volt bias on the Oxygen Sensor signal circuit which GM still uses to this day, But hasn't been included in cell diagrams for the last 25 years.

 

[JHZR2]

That's a 5 volt resisted bias.....Those high spikes you saw in the TPS voltage could have been Opens in the potentiometer which will spike to 5 volts.

For others reading this, a great set of drawings and teaching on resisted bias can be found here:

http://www.symres.com/files/scalebias.pdf

“Scaling and Biasing Analog Signals” Copyright Symmetric Research

It is copyrighted with explicit language about reproduction, so I can’t share screen captures. What we have is figure 4, I believe. A resistor divider with a biasing signal.