This is a funny story that happened while I was working on my wife Lisa’s car, 1996 Saturn SL2.
There was a problem with the alternator (previous post). I replaced the battery and the alternator, however the Saturn would not crank now. It was lot worse than I started working on the car. If the alternator is bad, would that cause the starter motor not to crank? My thought was that the car should run even if the alternator is bad, but the only difference would be that the battery would not charge.
I checked out the 1996 Saturn Chilton’s Service Manual from the library to look at the schematics. There was tons of wiring, but the relevant section was super simple. The diagram below shows the simplified version of the startup circuit.
1996 Saturn startup diagram
Not that many things to check for a failure. What happened was this: If I take out the IGN4 fuse out, the starter motor would crank, but the engine would not start since the IGN4 fuse controls the instrument panel, plus tons of other circuits like the fuel pump, etc. But if I put the IGN4 fuse in, the starter motor would NOT crank, but everything else seemed to be in order.
At first I thought that this might be a problem with the PCM (PowerTrain Control Module), but as you can see there is NO way that the PCM can intercept the starting circuit. Even if it were completely shut, the engine should crank.
This was a puzzle that I worked on for the next several days. The main problem was that there was no easy way for me to measure any voltages on the wires since they were all sealed up and they were very hard to access. I did not want to cut any wires.
But, I was not making any progress. So finally I inserted a pin into the yellow cable from the clutch switch. According to the schematic, this cable went into the ignition switch. When I did that, I could see that the clutch switch was working fine. Somehow, no power was coming from the ignition switch. Here is the picture of the pin inserted into the yellow cable.
1996 Saturn clutch switch
There was a number of problems working around the ignition switch. I could barely see it, let alone measure anything on it. I took the covers off around it fine, but I still could not get to it. The instructions were saying that I needed to take the steering wheel out, after disabling the emergency air bag unit. I wasn’t about to do either of those things.
When I carefully looked at the connector behind the ignition switch, I noticed that there were eight cables going into it. Number of cables agreed with the schematic I had, but none of the colors agreed. How could I know which two wires were the right ones?
After a long fight, I disconnected the connector from the back of the ignition switch. Now I could find at least one of the wires (the yellow wire from the clutch) that went to the ignition switch by checking the continuity.
The other wire was supposed to be coming from the fuse box (red-white). I removed the IGN3 fuse and put in a short blade and found the second wire that went into the ignition switch. Here is some pictures showing the 30 amp fuses.
1996 Saturn fuse box
1996 Saturn fuse legend
Note the relevant 30 AMP fuses on the right from top to bottom (Conv, IGN3, Blank, Blank, IGN4, ..)
1996 Saturn fuse terminal
Second fuse from the top is IGN3 fuse.
I found the two wires out of the eight wires this way. Then I noticed that all eight wires were going into another connector in the back. I yanked the connector towards me to have a better look. Seven of the wires were straight through into an identical connector. However, one of them (the one of the two I just identified as startup circuitry) was going into a small black box, and was coming out of it. This was the only other thing in the startup circuit path that could intercept the cranking.
I came into the house and asked my wife if she knew anything about this small black box. She said “Oh, I remember now, I had a burglar alarm installed a long time ago so that nobody can jump start my car. You just have to press the small button behind it”. Arrrgh!
When I pressed the small button, the car started right up without any problems. The colors of the wires from the second connector in the back matched the schematics perfectly.
When the engine started running, another question that I asked in the beginning of this post was answered. Will the engine run without an alternator? The answer is “YES”. Because when the engine started running, the two wires that connected into the alternator were dangling underneath the engine (waiting for me to connect them). As the battery discharges while driving, the PCM will notice that it was not being charged, and turn on the dash board battery indicator.