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Hi, new here, I have a 2002 base model manual transmission PT Cruiser. We've been stymied by the "idiot" light for the electrical system. Replaced the alternator and the control module (twice) but I still get the dash light intermittently after driving 3 or 4 miles. When I shut the engine and re-start the car I can go for miles without lighting the dash light, or, I can go for a few miles and have it re-light. Any suggestions as to something else that may be causing this problem? Or is it truly just the after market parts are less usable?

Thanks in advance . . . Joe Vee
 

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I'd look at the wiring and inspect every connection in the charging system from the battery cables to the alternator for corrosion.
 
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Have you tried to retrieve any diagnostic codes from the PCM (powertrain control module)? That is always advisable before swapping parts in hopes of solving the problem.
 

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Welcome to Allpar. If there is a battery temperature sensor issue, that can also turn on a battery warning light.
It is important to diagnose first, then repair/replace only what is needed.
What is your charging voltage? You can monitor this as you drive at the Power Outlet/Lighter socket.
Are there any fault codes present?
Turning the car off and then restarting it may be resetting the light, but a fault code should still be stored in PCM memory.
 

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Now, I don't know if this is true, but as a fellow PT owner, I've READ that somehow oil can travel from the oil sending unit to the PCM and cause problems. I don't know how it's possible, but on a PT forum that I belong to, this has come up and been discussed several times. The solution is removing the connector and giving it a good cleaning. You might look at that. I'm not saying that's what it is, but it's something to look at.
 

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The Electrical System Warning Light will come on for:
  • System Voltage too High
  • System Voltage too Low
  • Faults in the Alternator Field Control
Already mentioned, a bad battery or short can drag down the electrical system and cause the light to light. A short, even a corroded/dirty connector to the field control of the alternator can cause the light to light. Other components in the electric system, especially components that set the charging voltage can fail to light the light. The light does NOT mean simply you have a bad alternator.

What Control Module did you replace? You likely have several different ones in your vehicle. Was it the PCM?

Check for stored Diagnostic Codes, you can do a "key dance" that should display the codes in the Odometer Display, or flash the codes out on the Check Engine Light if you have a mechanical odometer.

Like mentioned already, check the system voltage.
The battery voltage with the car off.
The battery voltage with the ignition on but the engine NOT started.
The battery voltage (which is the system voltage) with the engine running.
Having a way to check voltage when the light lights also, like the cigarette lighter example already suggested.

The PCM controls the field windings of the Alternator to control its voltage, the PCM does what the old voltage regulator used to do. The PCM also takes in the temperature near the battery with a battery temp sensor, to determine what to set the voltage level at. The temp of the battery determines the charging/system voltage. Corrosion or an intermittent short to that one connector to the alternator to the PCM would cause intermittent problems.
 

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Now, I don't know if this is true, but as a fellow PT owner, I've READ that somehow oil can travel from the oil sending unit to the PCM and cause problems. I don't know how it's possible, but on a PT forum that I belong to, this has come up and been discussed several times. The solution is removing the connector and giving it a good cleaning. You might look at that. I'm not saying that's what it is, but it's something to look at.
Oil Pressure Sending units can often leak oil into their connector, oil flows easily, if the wire routing was just right, it would be possible for oil being forced into the connector at the oil press sending unit, to run along the wire and into the harness bundle and drain down to the PCM connector.

Does the Low Oil Pressure light and its sensor even connect to the PCM in an '02 PT Cruiser? They may NOT. Regardless, the wire for oil pressure would be in the bundle in the harness and oil could transfer.

The point is still valid. He has to figure out exactly what is going on.

First clue is stored fault codes.
2nd clue is the system voltages when operating normally and what happens to voltage when the light lights.
If voltage is going out of control or there is field control faults, with a new alternator, then I would be checking all the connections to the alternator, PCM and battery temps sensors.
 

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Discussion Starter #9
OMG, there is so much life here! Thank you all for your input. I don't do the work myself but I do have a mechanic who is helpful. A lot of the suggestions have been reviewed multiple times but I think we may need to look at some of the issues raised regarding connectors. There was an oil build up probably as pointed out. My mechanic dealt with that but maybe it needs another look. When the light is on with the engine running the voltage is at 15 or slightly hotter. It is my understanding that it should be around 14.5 so it looks a bit hot. I am printing out all of the comments so we can take a deeper approach. having replaced the alternator and computer twice I an loath to believe i keep getting bad parts. Thanks again to all who have shared their thoughts. i am overwhelmed :)
 

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Yes, the electric system warning lamp will light if voltage is too HIGH. 15V is usually more than its suppose to produce, 14.5V or 14.75V is usually the highest. And that is only if the battery temp sensor is telling the PCM that the battery is extremely cold. If the area around the battery is up around 65°F or more, you should be seeing more like 13V-13.5V.

Corrosion on a connector or ground to the alternator field control, or PCM, etc could introduce additional resistance that makes the PCM sense voltage lower than it really is and thus it ups the voltage higher.
 
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