97 Rodeo charging problem

1997 ISUZU
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1997 Isuzu Rodeo 92,000 miles 3.2L V6 Auto.
No output from alternator. Replaced alternator, still no output. In troubleshooting wiring I disconnected the red/white wire at the harness that goes to the generator gain control (in the ECU?). Alternator charges when wire is disconnected, will not charge if wire is connected. No voltage @ this wire KOEO or KOER. Should be 10.5v KOEO and Bat voltage KOER?
Short to ground inside ECU @ generator gain control? Must replace ECU to fix?
Jan 13, 2006 at 3:38 AM

What to check next

Diagnostic guidance. Suggested checks and possible repairs are separate from the owner's reported results.

The owner's final update points to checking replacement-part compatibility and operation before condemning the ECU. Have the original control wiring restored and verified against the correct service information.

Guidance references and applicability

Source: Original question and visible replies. Owner reports and other participants' experiences are distinguished. Next steps are editorial guidance for obtaining diagnosis or clarifying the reported findings; they are not a verified repair procedure or an independently confirmed component diagnosis.

Read the replies · Discussion summary and reported outcome

AI-ASSISTED GUIDANCE · REVIEWED BY 2CARPROS
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EWORKS
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OK-It's fixed. Turns out both of the NAPA reman alternators were bad. The internal regulators were not wired properly. The ISUZU alternator's gain control needs a 12v signal from the regulator or it will ground the regulator out. The NAPA alternators were not putting out any voltage through the red/white gain control wire. We installed a Carquest reman alternator and got the voltage signal we were looking for, the ECU was happy and the alternator was allowed to do it's job.
This was after 10 hours of diagnostic work! :evil:
Jan 18, 2006 at 11:39 AM

Discussion summary

97 Rodeo charging problem

A 1997 Isuzu Rodeo 3.2 had no alternator output even after replacement. During testing, the owner found that disconnecting a control wire changed charging behavior.

Reported outcome: The original owner reported that installing a different replacement alternator restored charging after two earlier replacement units failed to work correctly.

The owner attributed the earlier failures to their internal regulators. That explanation and the wire-voltage expectations were not independently verified; disconnecting a control wire is not presented as a repair.

Read the original discussion

AI-ASSISTED SUMMARY · REVIEWED BY 2CARPROS
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