QuestionQUESTION: I have a 1997 dodge Dakota with a 3.9l engine it has a high voltage issue with the tps. It is at 100% tps at key on engine off. I have replace tps as an obvious attempt I traced wires and then found no issues voltage at center wire which is trigger wire is higher than the voltage on the violet which is power. I even eliminated that wire directly to pcm and reads same coming directly from pcm. I determined must be internal pcm issue so I spent the money bought and programmed a new one only to find it is the same as when I started. I took it to a shop they spent hours and called and said they give up. I have unplugged everything I could imagine and have come up empty handy. I i unplugged clockspring o2 sensors iac map every sensor I could think of I unhooked fuses to no avail just sat at same voltage same issue IDK what is going on very weird. Any help would be greatly appreciated.
ANSWER: Hi Guy,
The signal wire cannot be higher in voltage than the violet power wire unless that wire is shorting to some other wire in the harness between the TPS and the PCM. What voltage does the signal wire show at the TPS plug when it is unplugged from the TPS? It should read 0V.
Have you tried unplugging both the TPS AND the pcm plug(s) and then measuring the resistance (or checking for continuity if you don't have an ohmmeter) between the signal wire and every other pin of the pcm plugs? I would believe you will find some other pin that is shorted to the signal wire or at least showing some other resistance than infinite along that harness run. There is no other way that I can see this happening. When you find such a short then check the wiring diagram to verify that the wire to which it is shorting does indeed carry the higher voltage that you are finding on the signal wire. You may have to splice in an alternative wire between the TPS and the PCM plug if you can't find the short somewhere along the harness. Try flexing all along the harness to see if you can eliminate the short and then open the harness where that flexing bears fruit to locate the short point. Please let me know what you find.
Roland
PS I am in a close race to be the 'volunteer of the month' here at Allexperts, so would appreciate your rating my answer. Thank you
---------- FOLLOW-UP ----------
QUESTION: I cut that wire off the pcm and the voltage was at 5.6v I replaced the tps to pcm wire and didnt change a thing. Thats why I bought a pcm thought an internal short... New one plugeed in truck started and light came back on.. Strangest thing i have ever seen. I do alot of in depth eletrical on new chassis for installations of dumps etc. I just dont understand this... Would you think the pcm plugs could short internally somehow? They seem insulated and very secure but idk whatelse to believe. I have no doubt something is feeding that pcm juice not of the tps circuit but how... Thanks
ANSWER: I am not in possession of a truck wiring diagram so I can't give you a totally knowledgeable answer but it seems to me that there should not be 5.6V on the signal wire with the tps unplugged. When you say that you cut that wire off at the pcm, do you mean right at the plug? If so, I assume that you didn't replace the entire harness between the pcm and the tps, correct?
So what I would suggest is that you measure for a short in the pcm plug(s) between the pin for the signal wire and every other pcm pin, for there must be a short inside the plug or between the pins/sockets of the plug which is putting a stray voltage on the signal pin. I understand that you have a new pcm so that should eliminate that as the source of the 5.6V on the signal wire. Also, when you measure the voltage on the signal wire it should be with reference to the sensor ground wire which is usually black/dark blue. Sensor ground may not be the same as chassis ground. You might also want to check the ground wires of the pcm to be sure they too are actually grounded to the chassis/-post as the case may be.
Roland
---------- FOLLOW-UP ----------
QUESTION: I have tested the wire with sensor ground as well as the chassis ground and it is close to the same still to high. I dont get it but I did notice the cruise control stopped working that offer any insight?
AnswerHi Guy,
That is interesting and a possibility. In a '93 car manual I have for the Chrysler car line I notice that the TPS wire is on pin 22 of one pcm plug while the vehicle speed control mode wire is on pin 23, right next door!. That mode wire will be carrying some voltage depending upon the position of the speed control or better yet it could be carrying 12v if the incoming 12v to the clockspring in the steering column were shorted to the outgoing mode wire. So that is a possible source of your constant high voltage on the tps. If it is clear which fuse powers the speed control unit you could pull that fuse and see if that solves the 0123.
Roland
PS You are entitled to rate this answer similarly as you did the first one this morning. Thank you.
