multimeter setting to test pin 41

[onlyoneromeo]

on the multimeter unit pictured in this message which setting do i put it on to test pin 41 to try n diagnose why im getting that generator terminal code ?

 

[steve]

I's expect you want to turn it to 20 DCV, three positions counterclockwise from the off position in the picture. You also need to move the black probe to the spot marked COM.

Do you know what your looking for in your testing?

 

[onlyoneromeo]

Thanx for the info. I think I'm looking for something like 9volts without accessories and s lil less with the. Running. Is that correct?

Also would I use that same setting if I were just testing the battery and alternator itself ? Or would I leave the black terminal where it is?

 

[steve]

There is nothing you would do with that meter and the black probe plugged in to where it is.
That spot is only for the red probe when making current measurements using the 10A setting that is next to the connector.

 

[DSM1G90]

With motor at idle, leads plugged into what Steve mentions and VOM setting at 20VDC: You touch both positive and negative leads to their respective posts on the battery and get DC volts coming from the battery .. which should between 13.8V and 14.3VDC .. which is telling you that the ALT is working normally.

 

[onlyoneromeo]

thanx dsm. now the reason why im doing all of this is because im trying to diagnose a check engine code. i was only getting 3.5ish volts at the ecu from the green wire coming from the alt. when i check the alternator wire up top im getting 7.5ish volts. should there be such a difference ? im really trying to get rid of this check engine code. is there anything i can do to get the correct value at the ecu? this is my second alt and it seems to be checking out fine but somehow im losing voltage down the line.

 

[DSM1G90]

You prob need to get a OBD-II test unit and goto this site: OBD-II Check Engine Light Trouble Codes

If you're getting the required voltage out of the battery mentioned above with motor running, bet you've something attached to your system that shouldn't be there, like an aftermarket alarm system (which loves to mess stock systems up), or a sound system that gobbles up voltage, or similar.

 

[onlyoneromeo]

Yes but at the plug coming from the alt I'm getting 8.7 ish volts down by the ecu I'm only getting 3.5 or so. Is there any place in the wiring loom that the green wire is spliced and might have a bad connection ?

Is there any place on the car I can draw from to get the required voltage to the ecu to get rid of this code?

 

[luv2rallye]

First, what CEL code are you getting? P1500?

Second, that green wire only goes from alt "FR" terminal to ECU pin 41 so it should have the same voltage at both ends when you keep it connected at both ends. Your not disconnecting one of the ends when measuring are you?

Third, that wire carries alt sensing voltage pulses (actually ON/OFF
state of the generator field coil) that the ECU uses to control the IAC during changing alt loads to maintain a constant idle (like when headlights are turned on). So it varies with alt electrical load and rpm. This function is for the oem alt and would not apply if you have some other one, like a non-turbo alt or a Saturn alt, or one that doesn't support this FR function.

Typical oem alt failures for P1500 are 1) open circuit in alt FR terminal circuit or 2) ECU. But if the alt is putting out like it should (charging battery > 13.8v) and idle is not drastically affected (like kills engine) when you turn on heavy electrical items at idle, then you can save yourself some money and not replace these. Of course if you really do have different voltages at each end of that wire when they are connected (at idle and with the exact same alt electrical load when you measured them), then you should find out why (partial short perhaps). Or you just want to get rid of that CEL code.

 

[steve]

i was only getting 3.5ish volts at the ecu from the green wire coming from the alt. when i check the alternator wire up top im getting 7.5ish volts.

Yes but at the plug coming from the alt I'm getting 8.7 ish volts down by the ecu I'm only getting 3.5 or so.

Were you using the meter with the probes plugged in as shown when you made these measurements?

 

[onlyoneromeo]

I did take the measurements with the probes as shown but after you told me I redid it and got the same numbers. I have to Make sure that line has current all the way thru and worst case scenario I have to run a new line from the alt straight to the ecu to see if it gets rid of that code. (p1500)

 

[luv2rallye]

Remember that line carries ON/OFF state of the generator field coil (pulses) which, when engine is running, will change with battery charging or any device being turned on/off (your meter reads an average). So you may get one reading on one end but by the time you switch to the other end it may have changed already. So test enough times to convince yourself that it is not changing much. Generally the more current the alt is putting out, the lower voltage (average) you will see on that wire (the voltage pulses are near 0 more often than they are near +12).

Another test: Do you get the same voltage on both ends with key On but engine not running?

Another possibility is you really do have a bad alt.

When doing voltage measurements, the black probe plugs into the COM jack and is connected to ground (car body/frame). The red probe, plugged in where you have it in the picture, is used for testing.