2002 Chrysler Town and Country Town and Country not shifting

The first thing you need to do is have the diagnostic fault codes read and recorded to know which circuit needs further diagnosis. That information was lost when you disconnected the Transmission Computer, but since the problem is still there with the new computer, it should have set the same code(s). You may be able to read them yourself as you can with engine codes. Cycle the ignition switch from "off" to "run" three times within five seconds without cranking the engine, then watch the code numbers show up in the odometer display.

Your test method is valid, if the vehicle was from the 1980s or before. For a 2002 model you're going about this all wrong. There is going to be a small current drain of as much as 35 milliamps all the time to keep the many computer memory circuits alive. When you disconnected the battery, the diagnostic fault codes, fuel metering data, and transmission clutch volume data were lost. Now you're going to have engine performance and transmission shift quality problems until that data is relearned.

More importantly, some computers need up to 20 minutes to go to "sleep" mode after the ignition switch is turned off. During that time it is common to find up to three amps for current draw. You can't measure current with a test light. All you can see is if you have enough current to make the light bright enough to see. The resistance of the bulb also reduces current flow to the point where a computer may never get to sleep mode.

If you're going to pursue this line of troubleshooting, you need an amp meter, but you have to start out on a scale high enough to read at least three amps. On most digital meters, that means moving the positive lead to a special jack. Once you see current drop after 20 minutes, you need to move the lead to the standard jack and lower scale to get more accuracy. Doing that creates an open circuit while the lead is disconnected. That wakes the computers up again and the 20-minute cycle starts all over. Most digital meters have a 2-amp scale and an internal 2-amp fuse. That fuse will blow due to the three amps the computers are trying to draw.

The next problem is you'll want to switch to the 200 milliamp scale for even more accuracy. All digital meters use a "break-before-make" range switch. That means as you turn it, the switch breaks the contact to one scale, then, as you turn it further, it makes the contact to the next scale. That momentary break is enough to wake up the computers again.

You need to insure there is never a break in that circuit when you do any switching. That is easy to do by connecting a small jumper wire from the battery's post to the cable clamp when any switching is done. We always do this with the negative cable. Once you're on the scale you want, remove the jumper wire so current goes through the meter.

As for code 1768, there is no real good description for it but it is related to the transmission relay. Typically you're going to find a broken ground wire for that relay, or damaged wires near the transmission or left inner fender.

Yup. There's three ways a solenoid pack can have a problem. The first is if the assembly is leaking, and that's usually a gasket problem. That is found strictly by observation. The second way is to have an electrical problem, which is almost always due to a break in one of the circuits. That can be a corroded terminal in a connector, a cut wire, a wire rubbed bare and touching ground, or less commonly, a break inside the solenoid's winding. The third way is to have a good circuit, but when it's energized, no fluid flows so no pressure increase is detected or the clutch pack doesn't engage. That is a mechanical problem related to operation of an electrical circuit. The last two defects will be detected by the computer which will set appropriate diagnostic fault codes.

I'm not sure what you're testing, but how do you get any voltage anywhere with the battery cable disconnected?

Wait a minute, I see the problem. Your positive probe is taking a reading related to a reference point, which commonly is ground, which is the negative battery post, but you removed that. This is like trying to measure barometric pressure with the gauge sitting in a jar pumped into a vacuum. There is some circuitry that is allowing the tiniest trickle of current through your meter, and that is what is allowing it to pick something up. You can prove this by measuring any of those voltages, then place a test light across the same two points. You'll see the test light doesn't light up and your voltmeter will go to 0.0 volts.

The only valid voltage readings are those taken with the battery connected. The battery does need to be disconnected to take some resistance readings unless the circuit can be made dead some other way, as in turning off a switch or pulling a fuse. Voltage in a circuit will cause totally incorrect resistance readings.

Terminals 30 and 87 are the contacts that are switched on and off. 12 volts on terminal 87 all the time is correct. That 12 volts will show up on terminal 30 when the relay is energized. Terminal 85 or 86 will have 12 volts when the ignition switch is turned on. I can never remember which one. If you have the relay plugged in and are able to reach the terminals with the meter probe, you'll find 12 volts on both 85 and 86. 12 volts is getting to the second terminal through the coil of wire in the relay. One of them gets grounded by the Engine Computer for one second after you turn on the ignition switch. It gets grounded again anytime the computer sees engine rotation, meaning cranking or running.

All of the testing you've done so far can be summed up with a single voltage reading. The relay has to be plugged in so you might have to fashion a thin piece of wire if necessary to reach the terminal. Measure the voltage on terminal 30. A test light works much better for this test for two reasons. First, most digital meters don't respond fast enough to catch quick pulses. Second, think of a compressed air line. All you need is a tiny pinhole through what is otherwise total blockage of the pipe, and you'll have full pressure on a gauge at the end of the line, but you'll never be able to get enough volume through there to run a tool. Similarly, all you need is any circuitry with really high resistance to let a teeny dribble of current through and the meter will pick that up as a voltage, but you'll never be able to get enough current through that resistance to do any useful work. A test light has very low resistance so it's going to draw relatively high current through the circuit. It can only do that and light up if the circuit is working properly. Also, we don't need to know the exact voltage at terminal 30. The test light is going to be off, (0.0 volts), dim, (insufficient voltage, but something), or bright, (enough voltage to prove the circuit is working).

There's two parts to this test. With the test light connected to terminal 30, it should be off. Now turn the ignition switch on. You should see a bright test light for one second, then it will go back off. You might hear the fuel pump's hum at the same time. That has just proven the circuit is okay and the Engine Computer has control over the relay. Next, crank the engine. The test light should turn on anytime the engine is rotating. If it does, move on to something else.

The only time a mechanic would do this test is if there was a fault code related to the "switched 12 volts is missing" and he wanted to verify that or see if the 12 volts was making it as far as the relay. That would instantly tell him if there could be a break in the circuit before terminal 87 or after terminal 30.

This is real hard for me to explain better without having a marker board to draw on. A better example might be to think about when you remove a battery cable to insert an amp meter. How can you get a reading of any current unless it is able to find a path through some circuitry on the car. Okay, now that we know there's some circuitry there, you're putting one meter probe on the battery's negative post, then the other probe on the negative cable that is attached to that circuitry and goes all the way around and back to the positive cable and battery post. In effect, you're measuring right across the battery, but with a pile of circuitry in between.

For all practical purposes, the voltmeter has extremely high resistance so it just measures electrical pressure, (voltage). No current actually flows through it. No air flows through a pressure gauge on a compressed air line. That's why it can measure full pressure when there's just that little pinhole in the blockage in the pipe.

If you tried to measure volume of air flow, you couldn't get any because of that blockage. You would not be able to run an air tool. The test light is that air tool. It needs current flow through it to make the filament light up. The circuitry in the car has way too much resistance to let enough current flow. That 's why where the voltmeter is showing 12 volts, the test light will show 0 volts. When you have the voltmeter connected and you're watching that voltage, it will drop to 0 volts when you put the test light across it.

You're right about lifting the relay out of the socket part way. All that's important is the terminals remain in contact with the terminals in the socket, otherwise it can't work. If you see the 12 volts show up on terminal 30, that can only happen if everything related to that relay is working. You can also stick a piece of wire in the terminal but you have to watch that it doesn't stretch the female terminal and cause an intermittent connection. That's a big issue with '90s GM relay sockets. Poking terminals with meter probes can cause the same problem.

First try swapping the relay with one of the other ones like it.

Next, what you described as intermittent operation suggests three likely possibilities. One is arced or pitted contacts in the relay. The next is intermittent loss of voltage feeding the coil of the relay. That is a Transmission Computer or wire issue. You said you replaced the computer already. The last suspect is the ground wire which seems like the best one.

Remove the relay, then use your ohm meter to measure the resistance between terminal 85 and ground. It should be real low, as in no more than a few ohms. If that appears to be okay, rig up your wire to measure the voltage on terminal 86 the way you did on terminal 30. This time it's a good idea to use the voltmeter instead of the test light. This is a very low-current circuit, and the driver transistor inside the computer may not appreciate being forced to pass enough current to run the test light.

For the moment we can assume the wire between the computer and terminal 86 is okay because you consistently saw the relay get turned on for a few seconds each time you turned on the ignition switch. What we want to see now is if that 12 volts stays there once the engine is running. Whether it stays or drops out will tell us which way to go next.

I think we're making some progress. Terminal 86 jumps to 10.5 volts, then drops to essentially 0 volts, which is correct, but it should go back up with the engine running. We have a problem there when it stays at 2 volts. It could be the computer is detecting a problem and is turning that voltage off on purpose to turn the relay off.

Terminal 87 must have 12 volts all the time. That comes right from fuse 15, a 20 amp, in the same computer module / fuse box as the transmission control relay. You posted:

RELAY IN KEY ON
Socket 30 ---11.8 dropping to zero and zero when running
Socket 86---- 10.5 Dropping off to 0.00 and zero when ruinning
Socket 87 --- 1.88

Unless you mistyped, you can't have only 1.88 volts on that terminal. The only thing that can cause that voltage when current is trying to flow is high resistance in that circuit. That would be like stepping on a garden hose a partially blocking it. As long as the nozzle is closed, you'll still have full pressure there. When you open the nozzle to turn on current (water) flow, the pressure, (voltage) will drop off. This is where a test light is more accurate. It needs current flow to operate where a voltmeter doesn't. Do this test again on terminal 87 with a test light. No matter what you do with the ignition switch, that test light should never go out. If it does, find that fuse 15 and test the voltage on it the same way. There will be two tiny holes on top for taking the readings.

Okay, terminal 87 is fine. It doesn't have a problem. The question now is why is terminal 86 dropping to 0 volts? My only guess at this time is the computer isn't happy about something so it's turning the relay off. What I would do next is remove the relay, leave the ignition switch off, then jump terminal 87 to 30. Listen for any clicking which would indicate there's nothing shorted in that circuit and things are trying to work. If you hear that, that's a good sign. If you don't hear anything, that's not a bad sign. If something is shorted, the 15 amp fuse is in there to protect the wiring.

If nothing goes up in smoke, remove the jumper, start the engine, then put the jumper back in. Along with all the other circuits that relay feeds, one line goes right back to the computer as its way of verifying the relay turned on when it expected it to, but it also wants to see it goes off when it's supposed to. If you leave the jumper in while you're cranking the engine, I suspect the computer will detect that, as far as it knows, the relay is stuck on, and therefore it has no control over it. By waiting to reinstall the jumper until after the engine is running, that will be avoided.

If everything seems to be okay, try driving the van to see if it shifts. With luck some other diagnostic fault code will pop up that may provide a clue as to where to look next.