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2001 Lexus IS200/300 Alternator Wiring

posted Jun 24, 2016 07:50:13 by Tim Canning
Hi Guys

A friend has asked me to look at his 2001 Lexus IS200 that he thinks has a charging/battery issue. I don't think they sell the IS200 in the USA but they do sell the IS300. I've checked the charging system diagrams for both and the alternator wiring is basically identical.

(Diagram has been uploaded, I hope it appears!)

If you look at pin 1 of connector B at the alternator, that wire goes to the Engine ECU. There is no detail on the diagram what this wire does - e.g is the wire used to monitor battery/charging voltage by the ECU (i.e there should be battery voltage on the wire with the engine running) or is it a control wire from the ECU to adjust the level of charging by the alternator?

I checked the Lexus technical information website but couldn't find a 'description and operation' section on the charging system.

Could anyone tell me what this wire does and what should be seen on the wire on a normally working system?



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4 replies
Andy@rscelectric said Jun 24, 2016 12:40:08
Hi: Unfortunately I can't expand the picture to see the terminals for some reason. If you find the make / model of the alternator, the manufacturers data sheet should tell you what each terminal does.
Electricity in Safe hands.
AndyMacFadyen said Jun 24, 2016 16:41:59
It is very likey to be Denso alternator in which case the small gauge B+ is the battery voltage sensing wire, the wire going to the ECU is an alternator load signal to the ECU to allow it to adjust idle speed for alternator load. The other wire is the rotor field energising which goes through the warning light (and on Denso there is usually a resistor in parallel with the lamp) to kick start the rotor field coil.

If it is the type I think it is the Engine ECU does not control the alternator charging.
Normally these alternators charge at about 14.4v at idle with no major electrical loads, at 2500 rpm with normal electrical loads on (dipped headlamps, heated rear window, heater blower on slow speed) the voltage should not drop below 13.4 volts. Also the charging voltage should never go above 15 volts.
You should check the field coil is getting energised and check the output on the main heavy gauge connection to the battery for excessive AC ripple.
Usually the most common problem with this type of alternator is diode pack failure, replacing diode pack is fairly easy if you have a very large soldering iron.
[Last edited Jun 24, 2016 16:46:29]
"Rust never sleeps"
Tyler said Jun 25, 2016 19:08:38
Andy MacFadyen is right on, pin 1 is a PCM input for idle control. I've seen a couple different Denso alternators with that circuit, and it's never a required input for charging. Usually, I find a 0-5V square wave at that pin, changing with engine load.

I experimented on my Scion, which uses a three-wire alternator of similar design. Pulling that circuit to ground with my test light made no difference to charging voltage, and set no trouble codes.

AndyMacFadyen said Jun 25, 2016 20:20:09
Yes it is a square wave the duty cycle of which changes with load. 50% duty cycle is no load, 0% duty cycle indicates the alternator rotor is at full field.
This capture is from a 105 amp Denso on a 1800cc engine at idle.
"Rust never sleeps"
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