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V1 Ark's City Goblin #187 (2008 SS/TC donor)
- bradr Well-Known Member
X3 in this case is GM's reference for "Connector 3". If you need help identifying the connectors, you can look a the first tab in my spreadsheet HERE. Find the connector in the left-most column and then scroll WAY to the right and you will see a column for "connector notes" which has color and other info.
ctuinstra
Goblin Guru
- ctuinstra Goblin Guru
Almost reminds me of a starter solenoid when the battery is dead. Enough power to energize the relay but once it's energized, it can't sustain it or what it turns on. Could be another poor connection somewhere. But just to be on the safe side, your battery is charged good, right?
Ark :D
Goblin Guru
- Ark :D Goblin Guru
I'm not 100% confident in the battery. It sat around for a few months without action, then a guy at work used it in his car for a week just to keep it alive, then it sat again for a couple more weeks in my garage. It puts about 12.5v into the car at any time, it looks like. Just to be sure, I hooked up my booster pack to it and it shows about 75% charge, so I turned the booster on and measured voltage again. 14.5v this time. But I saw the same behavior from the powertrain relay.
The fluctuating millivolts I am seeing on pins 3, 5, and 6 on the ECM connector would point to a short, would it not?
The fluctuating millivolts I am seeing on pins 3, 5, and 6 on the ECM connector would point to a short, would it not?
- bradr Well-Known Member
No, it just indicates there is no power there, would be expected by the power train relay behavior. I think it is likely you have a bad power connection or ground to the PCM. The PCM should be grounded to the engine block. Assuming it is, is your engine block grounded to the frame?
ctuinstra
Goblin Guru
Ark :D
Goblin Guru
- Ark :D Goblin Guru
I've tested the three large ground pins in the ECM harness, but if there are other grounds in there, I have not yet tested them. The engine block has the grounding strap attached, and I ground all the powder coat off the engine mounts before I bolted the engine to the frame, and the tester confirms that the block is grounded. I think it's more likely I have a bad power connection, somehow.
That thought had crossed my mind as well. In the course of all this testing, I've had the fuse box apart several times and I've been very careful to make sure it is all the way back together. I could see that being a problem, it's easy to do ... but I'm certain I have been seating it fully.
Ark :D
Goblin Guru
- Ark :D Goblin Guru
I just re-read though the last few pages of this thread, and the bolded above is sticking out to me. If pins 3, 5, and 6 in ECM X2 are powered by the fuse box, then correct me if I am wrong but, the power flow should look like this:
Battery positive pole -> Starter -> Positive pole on corner of fuse box
In other words, if pins 3, 5, and 6 are not getting power, does it not have to be a problem IN the fuse box, or with power delivery to the fuse box??
Ross
Goblin Professor
- Ross Goblin Professor
If there was an electrical issue between Battery positive pole -> Starter then the only things that would get power would be from that 50Amp fuse on the side of the battery.
Same if there was an electrical issue between Starter -> Positive pole on corner of fuse box
Ark :D
Goblin Guru
- Ark :D Goblin Guru
I definitely have 12.6v constant to the positive pole on the fuse box (14.6v+ with my booster turned on).
Yeah, I won't be doing that. I was tempted, but there's too much risk to the ECM.
The power steering message went away, but the CEL is not working, and in fact, the other lights stopped working too. The only light on the cluster that is working right now is the car security light (illuminates briefly at key on, then goes out). Gas gauge works briefly as well, now.
- bradr Well-Known Member
I know you want there to be power at these pins. And there will be, once your underlying problem is resolved. Here is how the system works:
The PCM needs power all the time, which you have now resolved. This powers the basic logic inside the PCM. It also needs power from the ignition and accessory circuits to determine key position (OFF, ACC, IGN, START).
When the PCM actually decides to power up all the engine periderals, it grounds the wire going to the power train relay. This powers up a bunch of stuff like injectors and also provides high current power to itself through pins 3/5/6 for all the sensors and high pressure fuel pump driven from the PCM directly.
Your Power Train relay behavior indicates the PCM is enabling the relay and then disabling it. This behavior is usually because of a weak power supply or a short in the wiring AFTER the power train relay that tanks the system voltage, causing the relay to drop out. The relay dropping out allows the PCM to power up again, and try and enable the relay again. This happens very quickly resulting in the relay chatter you are experiencing.
Desert Sasqwatch
Bigfoot Goblin
- Desert Sasqwatch Bigfoot Goblin
Ark, it helps when you have an expert's direction to help you through this. The help from the rest of us (mostly) wouldn't be as precise with what to do first, second, etc. and what not to do. 
Brad, the rest of us are grateful you have stepped up to help get Ark through this and taken time away from other important tasks, like family. Thank you and happy Father's day to both of you.
Brad, the rest of us are grateful you have stepped up to help get Ark through this and taken time away from other important tasks, like family. Thank you and happy Father's day to both of you.
