QuestionQUESTION: Your question was
1994 Dodge Grand Caravan 3.8L Stays In Limp Home Mode (LHM): Flash Codes 12, 15.
SYMPTOMS: Around 9 months ago, vehicle started to go into LHM without warning. It seemed to go into LHM more often when it was making uphill left hand turns and also while driving in the rain. Frequently, LHM could be cured by turning off the ignition and then restarting it. Other times, the car had to sit for awhile and then restart to cure LHM. One thing that was consistent, whenever the speedometer was not working the car would go into LHM.
Since LHM has become almost permanent: brakes not working properly; converter not releasing from lockup mode; and difficulty starting.
Approximately four months ago, the LHM condition has been almost continuous, with very few normal transmission shifts.
STEPS TAKEN TO REMEDY SITUATION: Replaced transmission solenoid pack. Replaced both speed sensors three times, verified continuity and resistance from speed sensors to TCM. Tranny fluid within specs. Added direct ground wire from TCM to ground terminal on battery; as well as used electrical contact cleaner to both wiring harness pin out and to TCM contacts. Brought car to “Transmission Expert” for free check ---their findings, power got up to transmission relay but no power from main relay box (drivers side fender well) upward. Per “Transmission Expert” it would take between 3 and 7 man hours ($300 to $700) to TRY to locate short. P.S. I have been unable to find (at Autozone or any where else) anyone who has the OBD1 scan service for free.
OTHER INFO: Transmission was replaced with completely rebuilt transmission approximately 60,000 miles ago.
QUESTIONS: What do you think is wrong? How best to get the transmission repaired in a cost effective fashion and/or is this something I could do myself (I am currently among the “No Longer Employed” portion of the U.S. population)?
ANSWER: This is a tough one. Your problem is almost certainly either a short-circuit or a bad connection at one of the weather-tite (HA!) connectors. Prior to OBDII, the flashing-light codes from the ECM were displayed on the dash, and none of the likely sources of "free" scans had anything other than a litle connector that shorted out the two contacts to make the light flash. You are almost certainly going to have to find someone who has experience working on older Chryslers and pay him to find your problem. The option would be to get a wiring diagram (most public libraries have them in repair manuals and will let you photo-copy them) and patiently trace each and every wire connected to the systems involved. Disconnect the battery and use the ohmmeter function to test each wire after it is disconnected at both ends. On these cars I would start with the wires that pass through the bulkhead connectors on the firewall, and on those that connect to the fusebox. These are trouble spots on all Chrysler front-wheel drives. This will be boring and time-consuming, but when you find and fix the problem you will feel great.
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QUESTION: I understand the idea of the ohmeter.. please tell me how to do it. Feel free to make it so simple that others also can use it for "Trouble Shooting Electrical Problems for Dummies."
Answer Well, this isn't the easiest thing to do if you don't have a basic understanding of electricity. So, I am going to assume that you do. An ohmmeter uses a voltage (from a battery contained in the instrument) to measure the resistance of a given piece of wire. If you have a recently purchased digital VOM (Volt-Ohm meter), it may have a circuit-fault detection mechanism already built into it. Consult the instruction sheet. If it has this feature, the meter will have a little buzzer that sounds whenever you make a complete circuit with the two probes. Test its function by touching the two probes together and listening for the beep. If it doesn't have this, or you have an old analog VOM, then you will want to set the dial for the lowest range of Ohms (the little omega symbols). When you touch the probes together the value displayed should drop to close to zero (in an old analog meter the needle will deflect completely). Disconnect each wire at both ends and hook one probe to one end and the second probe to the other end. You may have to make a jumper wire to reach that far (just attach two alligator clips to a long piece of wire) in some cases. Remember to disconnect the battery first. If the circuit is complete the value will go to zero, letting you know that there is little or no resistance and the circuit is complete. If possible, check the continuity through each connector in the same fashion. In places where that is not practical, pull the connector apart and make sure that the contacts are shiny and come together tightly. Eventually you will find a wire that does not cause a zero value, although it may register a few hundred ohms. Any value above 3 or 4 ohms is an indication of a corroded or damaged connection. In computerized cars there is much less than 12V available at most circuits, and DC voltage is not good at jumping across iffy connections. Make sure that all of the connections are good, all of the wires have complete circuits, and you don't skip any 'cause they're hard to get at. Eventually you should find the guilty circuit. After you do, you could continue to check all of the wires, or you could fix that one and go drive the car to see if it fixed the problem. I, personally, would go and drive the car right away unless the bad wire was part of a harness. Then, I would check the entire harness before I allowed myself to get excited and try driving the car. Remember to drive it 10 or 15 miles so that the computer, which has lost its memory from having the battery disconnected, has a chance to reset itself.
