96 LHS TPS issue

Been fighting this for a while so i don't recall if i got a code or not that
caused me to find it. but its been idling rough, off and on, surging,
shifting funky as expected, A/C compressor not working consistently, and a
few other issues. Some investigation online shows others have had this
issue...4.5 volts at the SIGNAL wire, with it unplugged from the TPS and key
on. So obviously the signal wire is shorted to a voltage source somewhere.
the connector to the TPS was cracked and causing all kind off issues but
that has now been replaced. Traced wires back to behind the block where they
run into the large main harness and none are stuck together. no voltage seen
prom the corresponding PIN on the PCM with power on, so i don't think its
coming from there. now the fun part? my test light works fine...if there's
voltage there it lights up but not on the TPS connector. But i can however
find voltage with the voltmeter. one of the weird things is ALLDATA is
showing a chart asking if its getting MORE than 10 volts on the signal
wire.....seems like a hell of a lot of voltage since 4.5 volts is already
enough to signal wide open throttle.

Tech at one of the dealers said to check all other sensors since some times
they can cause the issue as well. So far haven't found anything on MAP
sensor or trans control module, but haven't checked A/C pressure switch yet.
i am not looking forward to having to sort thru all those wires in the
harness, so I'm looking to find out if anyone else knows a known culprit
that causes this more often than others, so i can possibly cut the trouble
shooting time down.

 

That's because a test light pulls current (which will load the
relatively high impedance TPS output signal - test lights are only good
for stiff source voltages), a voltmeter doesn't pull loading current to
make its measurement.

Have you posted this to www.dodgeintrepid.net and/or wwww.lhforums.net?
There are some pretty good LH car experts there (some of the same
people hang out at both sites).

 

The PCM puts a 5v diagnostic voltage on the signal circuit. It's
normal. No, it won't light your 12v test light.

 

I'm on intrepid.net from time to time. seen some interesting stuff on
changing rack bushings and what not but nothing on this.....yet. i'll keep
looking though.

LHforum i didnt know about so that something to look into.

 

"The PCM puts a 5v diagnostic voltage on the signal circuit. It's

if this is so, how long is that voltage signal supposed to be there? it
appears to not go away key on, connector unplugged but my volt meter leads
are too big to probe the back with the connector plugged in so i haven't
checked it that way with engine running. still looking for some new leads
with thinner probe tips or the plug on type.

i tested for voltage at the corresponding pin on the PCM and there was no
voltage there? but that's with the PCM connector off. guess i really need
those meter leads....

 

I'm thinking if what you're seeing is not a diagnostic voltage, there
may be a bad ground connection into your TPS, or the ground side of the
sensor is open (rather than it being shorted to some voltage source).
The TPS is a simple variable resistor wired in potentiometer mode. If
the diagnostic signal (which I didn't know about) is staying on then the
question is what is keeping it on (bad PCM, or is there some condition
that is keeping the PCM in that diagnostic mode - perhaps once it
detects the bad sensor it keeps that diagnostic voltage on the sensor?).

I don't know that you can determine anything with the connector
unplugged, other than doing resistance checks back thru the sensor itself.

 

yeah ALLDATA shows several checks with the TPS and PCM connector off.
unfortunately some call for a DRB and i don't have access to one.

But i now that i re-read it, I see where at one point they are asking you to
use the DRB to monitor voltage and asking if the voltage is ABOVE 4.5 which
it isn't, but right on 4.5. Another check shows to disconnect the connector
and check for voltage at the sensor signal and asks if its over 10v. seems a
little high.

i need to find those leads today and get some more testing done. will
report back And by the way i think i saw a floating ground yesterday on the
sensor ground too so thanks for the reminder.

 

well my father in laws meter has leads with points on them to penetrate the
insulation slightly (i have a top class meter but the leads are kinda round
and blunt made to plug other connectors on them but i haven't found anyone
that sells them) and the TPS and circuit seem to be working just like
designed. here's what i should be getting:

THEORY/OPERATION
" The Throttle Position Sensor (TPS) sends signals back to the PCM in the
range of approximately 0.38 volts to 1.03 volts at minimum throttle opening
(idle), to a maximum of 3.1 volts to 4.0 volts at wide open throttle (WOT),
depending upon the throttle shaft angle. The PCM uses these input voltages
to determine the current position of the throttle. "

I got about .45 volts at closed throttle (or something close to that), and
it slowly increased as i opened the throttle, until i got about 3.8 at WOT.
So it looks like its working good and since i changed the connector Saturday
it seems to be doing ok. Still revs too high at start up...about 2000 rpm
but settles down to 950 or so. I had cleaned the throttle bodies and EGR a
while back when this all started so i need to look into the linkage and
springs to make sure everything is on correctly.

Thanks for the info guys, i'll report back later.

 

The PCM uses the voltage to monitor the TPS circuit. If it sees 5v
then it'll set a TPS volts high fault, meaning there's an open
circuit, the ground has been lost, or the TPS is toast.

The circuit is monitored whenever the key is on.

 

Pretty much what I said. But what is the diagnostic voltage you were
talking about previously?

The OP says it appears to be operating normally now - must have been a
connection problem.

 

yeah still idling high at first start up, but settles down and runs just
fine. TPS connector was causing engine to try and die at times especially
when you wiggle the ground wire (and i had changed connector once already,
so that one was bad too....watch what you buy at the salvage yard) and was
effecting trans upshift since it wasn't getting a good signal to the trans
control module. just like an old torqfilte it's gotta see the throttle
position to know when to upshift or down shift. i cleaned the throttle
bodies and adjusted idle screw setting because the measurement was off back
about 2 months ago. might put that back to where it was plus i need to
check one of the return springs i am suspicious of. I hear of folks
cleaning the IAC motor and valve but since i don't have access to a DRB to
adjust it if needed, i don't want to do anything with it just yet until i
check a couple more things.