QuestionQUESTION: I've had an ongoing problem with my 1999 Chrysler Cirrus. I've twice replaced the PCM (re-manufactured) and the Crankshaft Position Sensor. Both times the car ran great for about a month before it started to show problems again. The check engine light would come on, then go off without storing codes. Almost every morning when first started it would stall out. It would restart with no problem and run without stalling again (at least for a while). On occasion, it would stall when in low speed or coasting. It never stalls at high speed or while giving it gas.
Now the car won't start at all. It cranks but but won't start. There is a "No Bus" message on the dash. This is the exact same problem I had the last time (eight months ago) and was told I needed to replace the PCM and Crankshaft Position Sensor. Again, this did fix my problem for about a month. I then put up with the stalling issues for another seven months (though the symptoms did get progressively worse).
My question is, am I replacing the correct parts, and if so, why does it continue to go bad?
ANSWER: Hi Brad,
To correct this situation you may need to use a plug-in code reader that is capable of saying what is exactly the reason for No Bus showing up on the dash which could be caused by several different problems with the Data communication (Bus) system. About the only thing I can suggest would be to unplug each of the modules that are part of that system and obser ve whether the "no bus" message disappears when you remove each module, one at a time. If it does, then consider replacing that module.
Begin with the transmission control module, then continue after plugging it back in to remove and note the presence or absence of the message with: the powertrain control module, compass/mini-trip computer (if equipped), controller anti-lock brake (if equipped), the Heating/ventilation/cooling module, the radio, the body computer. One of those when removed may end the No Bus message. Other than a module, the twisted pair of wires that connect all these module could have a short or open connection but again that requires the sophisticated code reader to do that diagnosis. Were that the case, the best approach would be to locate a shop that is competent and equipped and have the vehicle towed there.
You can check the crankshaft position sensor by putting a voltmeter between pins 2 and 3 and then with the key in the run position rotate the engine by hand with a socket on the crankshaft pulley bolt. Observe whether or not the voltage oscillates between 5 and 0.3V. Similarly, assuming this is a 2.5L engine, connect the meter between pins 1 and 3 of the six-pin plug of the distributor and note whether the voltage does the same oscillations. If not then the camshaft position sensor is likely bad.
Otherwise, I fairly sophisticated diagnostic readout box will be necessary to diagnose the cause.
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QUESTION: Roland - thanks so much for the quick response and helpful advise. I wonder though since replacing these parts in the past (which fixed the problem for a month) any ideas of why it would eventually occur again in such a short period of time? Could there be an underlying problem that breaks these parts?
AnswerI doubt there is an overvoltage problem that breaks the pcm or the crank sensor. Rather I wonder if there is another bus module or wire connection situation that improves when a part is replaced but then deteriorates again. That is why a more sophisticated diagnostic readout make sense to me. But check out the two rotational position sensors (the crankshaft and the one inside the distributor) to verify that those are pulsing or not and replace but only after first verifying that you do have 8v on the other pin of the crank sensor and on the orange wire at pin 2 of the 6-pin plug at the distributor. That might get your engine running again.
Thanks for the rating/nomination and kind remarks.
By the way "no bus" could also mean that the connections of the bus wires to the cluster are compromised. You could verify that the connectors for pins 2 and 3 of the cluster plug socket proper are soldered to the adjacent circuit board. A 'cold' solder joint on either of those connections would provoke a "no bus" to appear even though there is no problem with the bus elsewhere on the network. So start by removing the cluster and touching those solder joints with the tip of a soldering pencil/iron to reheat the joints.
