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sprinkles08, Chrysler/Dodge/Jeep master tech
Category: Dodge
Satisfied Customers: 23118
Experience:  ASE Master and Advanced Certified, Chrysler/Dodge/Jeep Master Certified, Trans and Hybrid Specialist
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Exactly same thing as this post. But every thing he said to

Customer Question

Exactly same thing as this post. But every thing he said to check is good. Truck already has 2 new TPS sensors, and 2 New/reman PCM's, plus the original PCM. Still P0123
JA: Which particular sensor are you asking about? And have any trouble codes been triggered?
Customer: TPS sensor. DTC P0123
JA: What is the model/year of your Dodge?
Customer: 1998 Dodge Ram 1500, with a 5.9L V8 gas engine. Auto trans 4 spd, 4x4, a/c, cruise control
JA: Are you fixing your Ram 1500 yourself? What have you tried so far?
Customer: Truck already has 2 new TPS sensors, and 2 New/reman PCM's, plus the original PCM. Still P0123
JA: Anything else you want the mechanic to know before I connect you?
Customer: I have 5.10 volts on the tps signal wire going into the pcm. The pcm is putting OUT 5.10 volts, on what should be an INPUT signal from the TPS. disconnected every fuse and relay in the PDC, brake switch and clock spring are disconnected= same no change
Submitted: 2 months ago.
Category: Dodge
Expert:  sprinkles08 replied 2 months ago.

Hello and welcome to JustAnswer!

As you most likely know P0123 sets when voltage on the TPS signal circuit is high and out of normal operating range. This is most often the sensor itself, followed by a wiring issue.

Where are the replacement sensors coming from?

Do you have a scan tool to monitor live data?

When you measured the 5v on the signal wire was that with the sensor unplugged?

Customer: replied 2 months ago.
Snap on Modis scanner. Live data shows 4.98 volts for tps. Tps sensor unplugged, and signal wire cut at pcm. At cut point the half that goes to the tps= 0.00 volts, the half going to pcm= 5.10 volts. Using a fluke 88 DVOM.
Expert:  sprinkles08 replied 2 months ago.

It shows 4.98v on the scan tool with the TPS plugged in?

Customer: replied 2 months ago.
On scanner, data shows 4.98 volts with tps DISCONNECTED and CONNECTED same. Shows 4.98 volts with signal wire (wire coming from tps to pcm to tell how far you are on the gas, idle .5 volts- 4.5 volts at w.o.t) CUT 1 INCH AWAY FROM PCM CONNECTOR. The half from the to-do 0 volts, the half from pcm 5.10 volts.
Expert:  sprinkles08 replied 2 months ago.

At the time it's showing 4.98v on the scan tool backprobe the signal wire at the sensor with it plugged in. What voltage does it show?

Customer: replied 2 months ago.
Call. Way easier/faster.
Expert:  sprinkles08 replied 2 months ago.

I'm not able to talk on the phone. If the conventional question/answer format is insufficient I will need to open the question to see if another wishes to help.

Customer: replied 2 months ago.
Not at vehicle right now, to answer that question. ASE Mechanic by trade. Tps has proper 5 volt ( purple wire I believe), signal ground ( black wire with a tracer) good, signal wire (orange with blue tracer, I believe) good to pcm ( where I have it cut for testing) so for your question " what is the voltage on the signal wire with tps plugged in" .5 at idle or 4.5 volts doesn't really matter when the pcm is putting out 5 volts on the signal wire.
Expert:  sprinkles08 replied 2 months ago.

Yes, it matters what the voltage is at the sensor because that's how you're going to determine whether the problem is with the signal wire, the sensor, reference or sensor ground.

Customer: replied 2 months ago.
Again. The pcm is putting OUT 5 volts on the signal wire. The wire that is an INPUT to the pcm FROM the tps. So let's just say. The signal wire is cut, and I measure the signal voltage from the tps at idle (with tps connected. Remember I have proper 5 volt and ground.) And my reading is .5 volt ( normal) THE MOMENT I RECONNECT THE SIGNAL WIRE IT WILL READ 5 VOLTS, BECAUSE THE PCM IS PUTTING OUT 5 VOLTS ON THE SIGNAL WIRE. (This test was done with fluke dvom) (scanner will always read 4.98 volts because something is causing the pcm to put OUT voltage on what should be and INPUT circuit.) And that what I'm asking. What else other than a shorted clock spring can be causing this
Expert:  sprinkles08 replied 2 months ago.

I understand that you're seeing 5v on the signal wire at the PCM with the circuit open. That's normal operation for any sensor signal wire. It's pullup voltage for open circuit diagnostics and that's how it has worked since the 80's when electronic engine controls went into use. You can find the same reading at the coolant sensor, MAP sensor, governor pressure sensor, and intake air temperature sensor on this vehicle.

If you wish to continue I need the answer to the test I described.

Customer: replied 2 months ago.
TPS connector= pin 1- purple/white- 5 volt supply voltage- disconnected=5.17 volt. Connected (back probed)= 5.17 volt.
pin 2 (reconnected at pcm for test)- orange/blue- signal wire-disconnected= 5.13 volt. Connected=5.13 volt & no change on throttle sweep. Cut signal wire at pcm- perform throttle sweep test (key on/ engine off)= .6 volts at idle and 4.8 volts at WOT
pin 3- black/blue- sensor return/ground- disconnected= .01 volts/40.5 ohms (to neg batt terminal) Connected= .01volts/40.3 ohms, and no change on throttle sweep
Expert:  sprinkles08 replied 2 months ago.

There is a connector bolted down in the PDC. Disconnect this and use a spray contact cleaner to clean the terminals on both sides. Apply some dielectric grease, reinstall the connector and see if anything changes.

Customer: replied 2 months ago.
No moisture or corrosion in connector, have had connector off and on a few times for testing. Twenty plus years turning wrenches, an ASE master tech (GM dealership, Transmission shop's backgrounds) And this Dodge has kicked my A#*. Multiple issues found and fixed (ie: trailer light/brake connector at rear of vehicle chafed/corrosion in wires, same for trans connector, screw thru body harness under Left door sill plate from botched speaker wire installation, botched blower motor and resistor installation with a wire nut, wire nut connection of large red wire behind IP fuse block, who ever uses wire nuts for auto repair SHOULD NOT DO AUTO REPAIR) But the final culprit for my issue was what looked like an old critter home (ants, roach, whatever. Not mice) under PDC. Cleaned/blew out debris, inspected all wires, found what maybe chafe wires (4-6 ones but not to the point of exposed copper or corrosion, black taped them anyway). Possible short where nest was built into bottom of PDC in the connectors for the fuse and relays. How that didn't blow a fuse or cause other issues ???? Now on scanner data, normal TPS voltage with proper sweep voltage and NO P0123
Expert:  sprinkles08 replied 2 months ago.

Voltage was bleeding between circuits as it passed through this connector, whether it was at the connector itself or underneath. I've seen issues with ion channels in the connector itself which is why I recommended contact cleaner and dielectric grease.

Customer: replied 2 months ago.
As you know when you remove and re connect any connector, just that act re-scratches/ or cleans (to a point) the male and female contact points. Dielectric grease keeps moisture and corrosion (by product of moisture and electricity) out of the connection points which also can cause a "voltage bleed". The Top of the connector (or the point where the male and female connections happen) had no moisture or corrosion in it hence the "Voltage bleed" was not from That connection point. More than likely was due to the chafe wires under the PDC causing the "Voltage Bleed" or maybe even the old nest built into the bottom of the PDC ( although it was old and dry, and just dried dirt at this time). So blowing contact cleaner in the connector may have helped (didn't do that yet, but will do that and put dielectric in every connector I tested) Either way you mentioning that connector made me remove the PDC to look deeper because I didn't find the issue in the Connector on top of the PDC. Glad this one is over. Put this one into diag bag of tricks, and move one to the next project
Expert:  sprinkles08 replied 2 months ago.

I'm glad you got it repaired.