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ISC not working; possible problem with relay
Topic Started: Jan 27 2015, 01:02 PM (5,925 Views)
freegeo
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My ISC is not working right. The relay box has a spot in it for a ISCA relay. I pulled the relay and checked if it has voltage to it. Only one wire actually has battery voltage. Shouldn't there be two wires that have voltage at the relay. The wires going to it are Gray, Gray yellow, Gray black and White black or blue.

This is a 97 3/5 metro.
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Good bye


As with most relays, one should be battery hot and another should be hot either with the key or when that particular function is desired. If two are hot with the key on then then ground may be switched by the ecm, for example: the fuel pump.
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freegeo
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My 96 should be the same. I forgot to check it. It works correctly. I will check it tonght and see what it does.
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freegeo
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Found some info in the FSM on the wiring for the idle speed controller. I have battery voltage to the # 1 connector on the ISC relay (green circle on wiring diagram).

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I have tested the relay per the FSM and it checks out ok.

The # 2 connector on the relay goes back to the PCM. There should be battery voltage or close to that to the #16 connection at the PCM correct? IF not then I have a bad wire or connection between the relay and PCM.

I'll find out in the morning and post back the results.
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Good bye


It looks like the Pcm provides the ground to close that relay. From there the pcm controls the stepper motor, both other wires go through the motor and back to the pcm. The stepper motor looks like it is pulse width modulated by the pcm.
Edited by Good bye, Jan 28 2015, 01:44 AM.
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freegeo
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me and my metro
Jan 28 2015, 01:42 AM
It looks like the Pcm provides the ground to close that relay. From there the pcm controls the stepper motor, both other wires go through the motor and back to the pcm. The stepper motor looks like it is pulse width modulated by the pcm.
That's is what I was thinking also. If the wiring checks out to be ok then it has to be something with the PCM correct?
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truckjohn


When my ISC wouldn't work right - sometimes it wouldn't kick, sometimes it would kick randomly - it turned out the problem was my TPS.

Thanks
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freegeo
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truckjohn
Jan 28 2015, 09:46 AM
When my ISC wouldn't work right - sometimes it wouldn't kick, sometimes it would kick randomly - it turned out the problem was my TPS.

Thanks
Thanks truckjohn. I have put 2 different ISC (black box on the back of the throttle body) and they respond the same way. The last one I put on the throttle body was switched also. I had gotten a throttle body with ISC and TPS on it. No difference at all.
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freegeo
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Got some stuff checked out on the ISC. Used the FSM procedure. Was a couple of procedures I couldn't do since I need a dealer type of scan tool.

Here is what i found.

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There is battery voltage to the green circle. FSM shows this is good.

The wire is good between the 2 blue arrows (gray black wire).

The wire between the pink double arrow is good (gray wire).

The wire between the orange boxes is good (gray yellow wire).

On the ISC connector # 4 (red arrow) there is a reference voltage of 4.99 volts.

On the ISC connector # 5 ( yellow star) the ground is good.

There was only a couple of wires that I did not check. According to the FSM if all those things checked out the PCM is at fault and needs replaced.

The computer in this car (97) is a B5 1.0 MT Fed. The computer in my 96 is a B2 1.0 MT FED. They should swap out so I could see if it is the computer? I can get a PCM for $35 so it would be a cheap fix if that is it.
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Hanuman
"The Almighty Grounds Cleaner"

clean all of your grounds and all of the postive connections.
http://geometroforum.com/topic/5720306/1/

just because voltage is corect when tested doesnt mean it is corect under load. this is where a clean grounding system is critical. these arent 1990 subaru legacy's....the computer doesnt compensate well enough for voltage changes as these cars age and corrode.

i can you you from personal experience over and over again clean shiny grounds and positives are critical. a slight layer of corrosion almost impossible to see unless in perfect light is enough to effect the voltage while under load.
Edited by Hanuman, Jan 28 2015, 07:45 PM.
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freegeo
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i have already cleaned the grounds more than once.
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freegeo
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I went this morning and got some t pins at the fabric store. Figured I would do some more testing. I not stopping until I get this figured out.

I have so far added a extra ground from the battery ground to the intake ground. Made no change. I double checked and cleaned the grounds in the engine compartment.

I checked the reference voltage at the ISC connector with it plugged in and running it still has 4.99 volts.

The wires going to the ISC motor, (gray and gray red) I did not get any voltage but my voltmeter was set at 20 volts. I checked my 96 and didn't get anything with it either until I set it at 200 mv. I'll have to recheck it tomorrow and see if I get any readings set in MV. The reading did vary like a sign wave.

On a good note I did get my oil pressure switch swapped out so no more oil leak. WOO HOO! Made progress on something. :rocker :cheers
Edited by freegeo, Jan 29 2015, 01:30 PM.
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freegeo
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i did take and swap my pcm out of my 96 and there was no change.
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TripleThreat


THANKS GMF!
Edited by TripleThreat, Mar 14 2015, 11:04 PM.
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freegeo
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Yes I know my grounds are clean.

I checked my voltage at the battery post with the car running and all accessories off and get 14.48 volts. With the DRL on it has 14.23. My alternator is good and I know the grounds are good. Need more suggestions on what to check and how.


A guy at work has a friend that does tech work and has a dealer type scan tool that you can maybe hook it up and check out the problem.


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