Alternator - Code 42

92 XJ, 4.0L throwing code 42. A little background, when I start the engine in the morning (or anytime it's been sitting for a while) the guage shows low voltage around 9 or so and the lights are very dim. After a while, it's almost as if it the alternator "switches" back on and the lights will instantly brighten up and the gauge will snap to full charge. This is an intermittent problem. Some days it starts and runs fine without this problem. Other days it does it everytime I start the engine.

Any ideas? Bad ground, worn cables, alternator failure, etc?

You need to check the ASD (automatic shutdown) relay.

hmmmm....never thought of that. Think it's going bad? I have some spares.

Pop one in and see.

Well, it wasn't code 42. It was 41. My mistake. The manual says that the alternator field control circuit is open or shorted.

What the hell does that mean? Do I need a new alt? Anyone?

CJHVN said:

Well, it wasn't code 42. It was 41. My mistake. The manual says that the alternator field control circuit is open or shorted.

What the hell does that mean? Do I need a new alt? Anyone?

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Could just be a bad connection, a code don't mean that something is bad it;s just the place to start good troubleshooting practices.

langer1 said:

Could just be a bad connection, a code don't mean that something is bad it;s just the place to start good troubleshooting practices.

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I agree to check the connector on the back with the two small wires first. One of those wires goes to +12 volts (from the shutdown relay I believe) and the other goes to the computer, which grounds it to turn on the field current and cause charging. What the code means is that the voltage on the wire to the computer didn't match what the computer thinks it should have been. For example, 0 voltages when it wasn't grounding it means a broken circuit somewhere. +12 volts when it's trying to ground it also means a problem.