Welcome to Allpar. The 'Battery' light isn't wired like the charging lights of the past when it was in the battery/alternator circuit in series.

The lamp (LED) is turned on or off by the PCM over the communications bus.

That's why the lamp didn't go out while driving, even though it was charging OK. (In the old days, the charging light would dim, flicker & go out once it resumed charging).

Check for PCM fault codes related to charging:
P0622-GENERATOR FIELD NOT SWITCHING PROPERLY
P1594-CHARGING SYSTEM VOLTAGE TOO HIGH
P1682-CHARGING SYSTEM VOLTAGE LOW

There is also a section for diagnosis when no codes are found (DTC=diagnostic trouble code):
*CHECKING CHARGING SYSTEM OPERATION WITH NO DTC’S PRESENT .

Being a 23 year-old car, I would inspect underhood grounds & power cables for looseness or corrosion. Check drive belt.
Visit your friendly, neighborhood auto parts store.

 

when idling .. measure the voltage between the cylinder head to strut bolt/tower should be low<.1v

often the ground wire on the starter bolt gets corroded and needs a good wire brushing (via a drill) and the aluminum trans case too... for good measure i replaced the ground from the head to the body with a new wire from the head to a strut bolt

 

Thanks for the helpful info. Unfortunately, the system stopped charging entirely on the way back to the parking lot today.

I don't live where the car is located, so troubleshooting is difficult to accomplish. I'll have to try to get the car to a shop at some point.

 

The grounds on both inner fenders are known sources of problems such as this.
They were marginal when new and only get worse with age.
Also, the wiring harness containing the alternator wiring has been known to chafe through and short to ground.

 

. . . . Being a 23 year-old car, I would inspect underhood grounds & power cables for looseness or corrosion. Check drive belt.
Visit your friendly, neighborhood auto parts store. . . . .

. . . .The grounds on both inner fenders are known sources of problems such as this. They were marginal when new and only get worse with age. Also, the wiring harness containing the alternator wiring has been known to chafe through and short to ground. . . . .

While good ground connections are essential for proper operation of electrical components in a vehicle, a poor or intermittent ground connection is NOT the cause of the charging system failure in this situation.

The battery negative post wiring is grounded / attached to the engine block in the vicinity of the starter. The alternator receives its ground though its case mounting on the engine head. If there was a grounding issue, the starter would not engage but that is not the situation.

See attached image for PT Cruiser charging circuitry. 2002 model is the same as the 2001 model. The alternator field receives 12 volt power when the ASD relay closes. The PCM provides a pulsed ground side switch on the alternator field coil. There is a larger, 6 gauge wire that connects alternator output to the battery.

To diagnose this charging problem one needs to check the 6 gauge wire, through the fusible link, to the battery. Check for broken wire or short to ground. Likewise with the 2 wire cable to the alternator field check for broken wire, connection and / or short to ground.

If wiring passes all its inspections, then the alternator needs to be tested for failed brushes and failed diodes.

 

Thanks again for the comprehensive info.

Unfortunately, the car is located in another state, which makes troubleshooting logistically difficult. I'm going to try to get there in the next few weeks to bring it to a shop.