QuestionHi, Roland;
My GTC has 94,000 miles on it, I installed a rebuilt A604 last fall and retrained it. The trans was rebuilt by an independent jobber in northern Utah and according to the paperwork, a Mopar approved shop. I am using the correct trans fluid, btw, and the level is full.
Now, I've got an erratic speedometer and limp mode when the speedo quits. There is no rhyme or reason to it. Sometimes, I have normal operation on start up and sometimes it's in limp mode (no speedometer, usually, but not always). I have done restarts that occasionally get the speedo going, then another is required to get the trans shifting again.
I've replaced the output sensor, cleaned, inspected and tightened the wiring plugs on the transmission harness, the ground connections are cleaned and I've used some anti-oxidant electrical lubricant (conductive) to keep them rust free.
I do not have access to a code reader, usually there are no abnormal codes (very occasionally I get a 37, but it disappears if I can get the trans to shift through one complete cycle), the nearest Chrysler dealer is 120 miles away, and I'm about to sell this darn car if I don't get it fixed soon.
I appreciate any advice you might have. Thanks in advance. I sure miss my slant six Valiant . . .
Charles Cochran
AnswerHi Charles,
I am limited in having a '94 manual rather than a '95 but I doubt there is any difference between the two.
The fact that you have a limp-in which certainly can be caused by the loss of the output speed sensor signal at the same time that you lose the speedometer function strongly supports the possibility that either the output speed sensor is not being driven reliably by the trans gear, or that the wires from the sensor to the TCM or to the speedometer are not reliably connected. I would suggest that you trace those wires and check their continuity while shaking the harness that contains the wires. Here are the wiring details:
The dark blue/black wire at the sensor is connected to pin 13 of the TCM and it is a common (-) source also for the turbine speed sensor. The sensor signal is light green/white and goes to pin 14 of the TCM. There may be an issue in the TCM but only a trans controller readout with a DRB II would tell you that.
The speed sensor signal is digitized in the TCM and sent on the data bus (+) violet/brown at TCM 43 and bus (-) white/black at TCM 4 to pin 26 at the PCM (+) and pin 46 at the PCM (-) respectively. There is one disconnect plug,light gray 10 pin, on the right side fender shield that those two data bus wires pass through in going from the TCM to the PCM. That data bus signal is used by the PCM for engine control, but not for the speedometer signal. That is generated in the TCM on a white/orange wire at pin 58 of the TCM, through a black 10 pin disconnect plug on the right inner fender shield to a splice under the dash where it is split between the speedometer (black plug pin 5) and the PCM pin 47. I am not certain how the speedo signal differs from the output sensor signal, if at all, nor exactly what the PCM uses those signals for. I suspect the data bus is for engine control while the speedo signal is for the cruise control.
If the wiring proves to be reliable, then I would wonder about the TCM being flaky, or the output sensor being flaky or the trans gear not driving it properly.
It might be necessary to get a readout of the data link plug under the dash to see what codes are stored in the TCM to get a better handle on the malfunction, though I know that is impractical. The fact that the separate speedo and data bus signals originate in the TCM and are separate wires would cause me to think there is a problem within the TCM, or in the wires from the output sensor to the TCM.
I don't know whether this description and analysis is something that you already know or not, but it is my best effort to give you some direction.
Roland
