I PUT A NEW PCM IN THE CAR IT TURNS ON BUT RUN ...

2002 Dodge Durango

Tiny

trishaannafalcon

November, 9, 2012 AT 9:45 PM

I put a new pcm in the car it turns on but run roughly and the dash board stays lit up and no gauges work, if I were to put the old pcm back in woul it have to be fix for what the odometer says

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24 Answers

Tiny

caradiodoc

November, 9, 2012 AT 10:46 PM

The vehicle's mileage is stored in the instrument cluster. You can read the mileage in the Engine Computer too with a scanner but that is not for the odometer.

Tiny

trishaannafalcon

November, 10, 2012 AT 12:27 AM

Ok so another qustion we put the new Pcm in but the truck runs like crap and none of the gauges work and all the light sensors light up and don't turn off. But they were working just fine before we put the new Pcm in.

Tiny

caradiodoc

November, 10, 2012 AT 5:26 AM

Don't have an answer for that. Chrysler has very little trouble with their Engine Computers. What was the original problem or reason for replacing it?

Tiny

trishaannafalcon

November, 10, 2012 AT 7:03 PM

The reason for changing was it started to turn off and it would crank but no start say no bus and no gauges worked so we did all the tests and to no prevail so only next option was to. Changethe pcm.

Tiny

caradiodoc

November, 11, 2012 AT 3:57 AM

The "Data Buss" originates in the Body Computer. It's a pair of wires that connect all of the many computers to each other so they can share information. Roughly 6.0 volts is on both wires. That's what comes from the Body Computer. Anything that shorts one of those wires to ground or that shorts the two wires together will cause the buss to not work and none of the computers, including the Engine Computer, will get the turn-on signal to start working.

We were taught that any computer on the vehicle could develop an internal short that could kill the data buss and result in a no-start condition, but in my experience there's too much circuitry in them isolating a potential short from the buss. I've never run into a different computer itself causing a no-start. The problem is most commonly caused by the Body Computer or its connector terminals not making a good contact.

Tiny

trishaannafalcon

November, 11, 2012 AT 8:14 AM

So what do you recommend the gun the truck to start in runs but it's running rough then again just work all the sensor lights in the dashboard but still it the alternator is still kinda whinny and doesn't shut off like before although the way it runs it sounds like its getting ready to die out kinda like when you run out of gas.I'm running out of ideas.

Tiny

caradiodoc

November, 11, 2012 AT 8:58 AM

Wow, that's quite a sentence. Depending on how I read it, it got the rough running and a hint of low idle speed. The low idle is due to disconnecting the Engine Computer. (Disconnecting the battery will cause the same low idle speed).

The Engine Computer lost its memory and has to relearn "minimum throttle" before it will know when it must be in control of idle speed. It also might not give you the normal "idle flare-up" to 1500 rpm when you start the engine. To meet the conditions for the relearn to take place, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the brake or gas pedals.

For the rough running I'd start with normal tune-up stuff like spark plugs and wires. If the Check Engine light is on, there will be a diagnostic fault code stored in the Engine Computer. Those codes will get you to the circuit or system that needs further diagnosis. There are some codes that indicate which cylinder is misfiring.

Tiny

trishaannafalcon

November, 11, 2012 AT 10:54 AM

Sorry I did not proof read the last message. But there still leaves the problem with dashboard not working none of the gauges are working at all. They were working on and off when the old pcm was in. The only time they woul't work was when the truck didn't want to start and now the truck starts up no but none of the gauges are responding at all. Hopefully this can be fixed

Tiny

caradiodoc

November, 11, 2012 AT 11:14 AM

That goes back to the Body Computer. He gets the information from all the other computers, then sends it back out on the data buss. The instrument cluster receives that information on the buss and picks out what it needs to run the gauges.

If you see "no buss" in the odometer display, the cluster isn't getting information from the Body Computer. To not overlook something simple, measure the battery voltage. If you find around 11 volts, it has a shorted cell. Low system voltage can prevent the Body Computer from working or will make it do strange things.

Tiny

trishaannafalcon

November, 11, 2012 AT 12:37 PM

Thanks a bunch we are going to check all and if I still have an issue I will be sure to come back with some more questions. Thanx

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