Hi. I have a 2000 Dodge Caravan 3.0L. Recently when driving the car I experienced a couple of hard jerks while driving down the highway activating the check engine light. When I got it home the vehicle would not start. The starter relay under the hood would only chatter as soon as the ignition would turn on. I swapped out relays and the same problem. Now the interesting part is when I plug in the OBD reader the engine fires right up and runs smooth. I replaced the O2 sensor which the reader stated was a problem. That was the only code and the check engine light has cleared. Still the car will only start when the reader is plugged in. If I disconnect the reader while the engine is running the engine quits. Obviously By plugging in the reader I am bypassing a circuit somewhere allowing the engine to start. No doubt a missing ground. I do not have a shop manual so at this point I am only guessing as to where to look. I am very good with a multi meter but where to begin? Oh another thing, the instruments are flashing periodically when the engine is running. This started a week or two before the check engine light came on. The speedometer, fuel gauge, odometer would fluctuate and then normalize for a while. Again I think there is a missing ground somewhere. Your thoughts? My thoughts are a possibly bad wiring connection on the ECM or a bad ECM itself
What is the mileage of the vehicle?
Mileage is 145,000. Original miles as I am the original owner. The O2 sensor replaced is the upstream sensor. No O2 sensors have been replaced in the past
Found the problem. The Negative battery post has two cables running to it. The larger one which is clamped to the battery and a smaller cable about AWG 16 connected to the side of the wire terminal clamp. This smaller connector fastened to the side of the post was pretty corroded at the attachment point. Once cleaned with a wire brush and CRC cleaner sprayed on it all is good. This smaller wire goes into a bundle on the main negative wire about eight inches downstream from the battery post. I don't have a wire diagram but I assume this smaller wire branches off to the ECM or perhaps a ground on the chassis somewhere which supplies a ground to the ECM amongst other devices. Anyway plugging the OBD reader into the diagnostic port obviously replaced this ground allowing the engine to start. This is good to know as should this connection go bad in the future it could leave a person stranded. A simple jumper bypass at the diagnostic port can have you back on the road..... PROBLEM SOLVED!
Thanks for taking the time to share what you found out. Good luck.
Just leave it plugged in.
I think a bad ground is your problem. I would start with the ECM ground.
