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V1 No Start, Was Working
- glantz Member
That’s a good thought. I will try it. I’m currently measuring 12.6 at the battery, same at the fuse box post. I’m only measuring 9v at the ecm power pin. I’m not sure what it should be. I would assume 12v but trying to find conclusive documentation. If it’s supposed to be 12v then that could be the issue and I’ll have to trace it and see if I can find a break or something. Best lead I have so far. It’ll have to wait until tomorrow. For now I’ll throw the charger on.
Goblinfanclub1234
Well-Known Member
- Goblinfanclub1234 Well-Known Member
I cleared up a bunch of intermittant issues I was having by running a nice thick ground wire from the engine block ground location to the ground bolt at the rear drivers side of the car.
- glantz Member
I used a small jumper wire and probed pins 3, 19, 20 and 73 on X1 connector (with the other probe on ground lug). According to the diagram those are the four that supply power to the ECM. First three measure 12.49. Pin 73 still only ~9v. If I measure at the fuse it is also ~9v. Should it be 12v? Am I testing correctly?
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- Gtstorey Goblin Guru
Yes, it should be getting battery voltage. Pull the fuse and check voltage at the fuse. It may be the power train relay feeding the circuit that isn’t making good contact, either internally or externally. Or it could possibly be a failing circuit in the fuse box.
I’m not sure this will be your main issue, but needs to be corrected regardless.
I’m not sure this will be your main issue, but needs to be corrected regardless.
- glantz Member
Fuse box failure would explain a lot since this stopped working so suddenly. I keep coming back to the suddenness... it was working perfectly, then in an instant (while attempting to start) it wasn't. Like something blew or failed. Blocks are definitely tight. What I plan to do is remove the fuse box clean and reseat all contacts and see if that makes any change. I'll also do some additional troubleshooting on the fuse box itself. Last night I noticed that a couple other fuses in the area surrounding the PCM/ECM fuse measured ~9v at the fuse. It was late and I didn't identify which fuses or how they relate to the circuit.
Desert Sasqwatch
Bigfoot Goblin
- Desert Sasqwatch Bigfoot Goblin
This sounds like a trace on the PCB inside the fuse box overheated and has resistance now, but didn't go open circuit all the way. Since just about everything else has been checked, I would recommend separating the fuse box itself and have a close look at the PCB - since you are removing it from the car anyway. Anything that looks like a dark/burnt line in the green board may be your culprit.
- Gtstorey Goblin Guru
Or like a loose connection stopped making connection. Electrical problem always happen suddenly, no matter what the cause is. Other than maybe a failing battery.
To trouble shoot electrical issues, you have to be methodical. Once you find an issue, just follow the chain. Low voltage at the ECM, leads to low voltage at the fuse, to the relay, to the fuse box, and continue on to the battery. Keep going till you get the battery voltage. I also recommend running a wire straight to the negative post of the battery as a temp ground so you can insure that grounding issues aren't causing bad readings on your voltage. Or at least take all of these readings at the same ground point.
To trouble shoot electrical issues, you have to be methodical. Once you find an issue, just follow the chain. Low voltage at the ECM, leads to low voltage at the fuse, to the relay, to the fuse box, and continue on to the battery. Keep going till you get the battery voltage. I also recommend running a wire straight to the negative post of the battery as a temp ground so you can insure that grounding issues aren't causing bad readings on your voltage. Or at least take all of these readings at the same ground point.
- glantz Member
I 100% completely agree with this and it is my plan. I will keep working my way through it. I also agree that electrical always happens suddenly. Still the way this happened seems meaningful. It's not that one start attempt worked and the next one didn't. It's that it was mid-start while the starter was cranking when all ECM communication stopped that has me convinced something failed. I'm not so convinced that I'm not looking at all possibilities but it does seem most plausible to me. I am definitely going to keep tracing until I rule out all possibilities (or replace anything else).
- Gtstorey Goblin Guru
Just the vibration from the motor cranking can make a loose connection break.
I was once trouble shooting a natural gas heater that drove me crazy because the slightest touch of the heater would make it start working. My Fluke meter magnet touching this 300 lb heater woulkd make it start working again.
I was once trouble shooting a natural gas heater that drove me crazy because the slightest touch of the heater would make it start working. My Fluke meter magnet touching this 300 lb heater woulkd make it start working again.
- glantz Member
Update: I think I have isolated this problem to the fuse box. I get battery voltage on x8(jump post), as well as all leads on x4 fuse block. Low voltage seems to be just the circuit for the PCM/ECM fuse (x5 block). Actually, there are other fuses in the surrounding area also with low voltage but they are unrelated to the ECM circuit (still concerning). So this seems to be a problem with the fuse box. I'm going to take the weekend to triple check everything to be certain before I order another. I still haven't visually inspected the PCB. I did connect to the ECM through GODIAG (I posted about that in a separate post) and was able to pull DTC, so it's for sure not the ECM itself. Some of the codes indicated previous low voltage warnings so that's definitely something. I'm on the right track I think.
Desert Sasqwatch
Bigfoot Goblin
- Desert Sasqwatch Bigfoot Goblin
If this ends up being a burnt circuit trace on the PWB in the fusebox, the source of the problem needs to be located so a new fusebox or a trace repair doesn't result in a repeat. In most cases, a burnt trace is the result of that circuit being shorted to ground and pulling more current/amperage than the trace can handle. The connection to the fusebox and wiring associated with this circuit should be checked with an ohmmeter to look for shorts or very low resistance to the frame ground points.
When you have located the burnt trace on PWB inside the fuse box, it can be fixed if you have soldering skills. Cut the burnt trace out of the circuit and solder in an appropriate wire to bypass this bad circuit - 22 gauge wire if it's a narrow looking trace, 16 gauge if it's a thicker looking trace.
When you have located the burnt trace on PWB inside the fuse box, it can be fixed if you have soldering skills. Cut the burnt trace out of the circuit and solder in an appropriate wire to bypass this bad circuit - 22 gauge wire if it's a narrow looking trace, 16 gauge if it's a thicker looking trace.
