| ID | Status | Date | Year | Make | Model | Transmission Type | A/C Controls | Public/Private |
|---|---|---|---|---|---|---|---|---|
| #14633 | Closed | 2003 | Chevy | Venture | public |
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I took the alternator off and had it tested at my local parts store and they said it was good. There is an orange and a red wire coming out of the back of the alternator. The orange wire has battery voltage and I know the red wire goes to the ECM but I don’t know what the voltage is supposed to be. Also the ECM was replace a couple of years ago. Any suggestions you can give will be greatly appreciated. It didn’t ask below but it is a 3.4L V-6 |
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Testing on this system is a bit of a pain because according to GM you need the use of a scan tool with bi directional controls.
Does the voltage measure greater than 4.7 volts when commanded ON and near zero volts when commanded OFF? What one can infer from this is there should be a nominal 5 volt signal on the red wire when the pcm wants the alternator to charge. Care should be taken since the engine will need to be started and running to test this signal without the use of a scan tool. You may want to inspect the terminals in the harness connector to see if they are compressed and therefore not making a connection to the regulator terminal. Also check to see if the wire may be broken near the connector. |
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I don’t have 4.7 volts coming out of the alternator to the ECM. I only have a little over 1 volt. Are those two wires, the incoming voltage and the outgoing voltage plugged into the regulator? Or does this not actually have a regulator in the alternator? Thanks. |
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The 4.7 or higher voltage is produced by the PCM and is measured with the alternator connector disconnected and the scan tool commanding it on. The hope is that the PCM will still send this signal with the engine running and the harness to the alternator disconnected. |
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I don’t have a scan tool that can command. I measured with the voltage with the connector plugged in and the engine running. I will try it with the plug out and see what I get. Thanks. |
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I tried it with the plug out and it still did not register the 4.7 volts. It was around 1.5 volts. I did check the resistance on the wire |
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There is a lot of gray area here. According to the GM test you need to use a scan tool in order to “see” the 4.7 volts or higher with the harness disconnected. Although it likely should there are few things to consider. Is the battery voltage low enough that the PCM would automatically adjust the voltage? Does the connector need to be connected to the alternator and immediately disconnected after start up to test? Although most sources will recommend using an ohms test to check the wiring it is a very poor test. The wire needs to be isolated and a load test placed on it with a headlight bulb as the minimum load used. |