voltage problem

Hey all,
Got a problem with my electrical stuff.

Was driving today and noticed that the check engine light was on and my battery gauge was in the red. When I stopped at a light or idled in a parking lot, the gauge crept back up to 12 or 13, then dropped again once I started moving.

This seems counterintuitive. Any ideas?

patient is a 95 cherokee, i6 manual, 165k 2 dr.

Sounds like a low voltage issue from:

• a failing battery
• a failing alternator
• dirty or loose wire connections
• internally corroded battery wires

Perform routine maintenance of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Copper wires should be copper color, not black or green. Do the same for the grounding wires from the starter to engine block, and from the battery and engine to the Jeep's frame/body. You must remove, scrape, and clean until shiny, the cable/wire ends, and whatever they bolt to. Jeeps do not tolerate low voltage, bad connections, or poor grounds.

Test voltage drop with a digital volts/ohms multi-meter, set to lowest scale on volts. Place the negative lead on the battery negative post, and the positive lead on the alternator. The reading is how much voltage is draining. You should see a reading of .002 volts or less depending on the meter. Anything greater and you have ground connection problems.


Have the battery and the alternator Load Tested for proper function in a test machine that applies a simulated work load. Handheld testers are inaccurate and will often pass faulty parts.

I would start with the grounds, when the engine torques you could be losing connections, could be charging circuit in the PCM. On rare occasions we have seen a flying short in the rotor cause no output, but the majority of the time it would cause runaway voltage.

First I would check the battery voltage at the battery, engine off, should be about 12.7 V. Charge the battery if it is low (and clean the battery cables). Then check the battery voltage at the battery with the engine running. Should be about 13.7-14.5 V.

Then do the wire testing, and other main wire contact clean ups already suggested. And maybe retest again.

Keep in mind Jeep gauges are not always right, especially the Volt gauges.

Check the O2 sensor wires for a broken, damaged shorted wire!!!