Can the ECU be started with a power supply?

[TurboWood]

Hi Gents,
I apologize if these are simple questions, but hopefully you have the patience to deal with another newb.

I'm building a kit car and haven't finished the wiring but need to get the PCM powered up. The main reason is I've bought a used PCM and I want to make sure it works. The second reasons is that despite using HPT I also need to load a trifecta tune that will eliminate the security since I'll have no BCM. I would like to get that loaded as well. Trifecta has assured me this will still allow me to tune with HPT so you'll be hearing more from me once the car is running.

To do this I am intending to wire up the GM LAN (OBDII port) and use a 12V power supply. Does anyone know if this is possible? From what I can tell I would need to wire it as follows:

Power to pins: 3, 5, 6, 54, and 56 on the small connector
Ground to pins: 1, 2, and 4 on the small connector
High speed LAN (+) to pin: 42 on the small connector
High speed LAN (-) to pin: 55 on the small connector
Nothing connected to the large connector

Is there anything else needed? Will the PCM throw up tons of error codes and puke or will it allow me to do this?

As I'll have no BCM is there any way for the PCM to calculate gear? I have a wiring diagram that I bought online that will allow me to run the engine in stand alone, but I see no wheel speed sensor so I assume that is part of the BCM. Can any tell me what pins on the PCM are linked to gear?

Thanks,
Daniel

[Engineer@HPT]

PCM type?

[cobaltssoverbooster]

Trifecta required for bcm delete would make that a bosch e69 gdi controller.

[TurboCobalt]

At the very least you'll need to also wire in accessory as well as run/crank line. If u need more details on what these 2 lines do let me know. There may also be some other wake up line? Not sure, I can't think of any right now. If i were u id check every pin on both connectors and be ready to connect to any and all other lines that say something like power, 12v, or ground. Im not sure how many different power sources, and how many different ground planes the controller has. It should only be the ones you stated but who knows. Also make sure u use a twisted pair for the CAN bus, and you'll probably need a termination resistor. I can't remember exactly but I think it's either 120 or 60 ohms.
Good luck, let us know what happens.

[TurboWood]

I'm very glad I asked!

overboost is right, the PCM is from an '08 Cobalt SS. I'm using an LDK longblock from ZZP.

TurboCobalt,
I do need some more information. Looking at the wiring diagram the only thing I see labeled "accessory" is not used anymore (pin 41 on small connector). Am I correct that only the + side of the GM Lan needs to be a twisted pair? I don't see anything labeled run/crank.


Regarding vehicle speed, I may have found it. It looks like there is a sensor connected to pins 40 and 53 on the small connector. Does anyone know what the cobalt speed sensor input is (counts/rev?)?

Thanks,
Daniel

[maccos]

Hi Daniel,
Scott from ModernKitCar.com....where you purchased the standalone wiring diagram.

Yes it sounds like you have the correct pins for power and ground to power up the ECU. But you probably only need the first 6 pins wired on the 58-pin-connector as those are the BIG pins.

The two wires from pins 42 & 55 are twisted around each other from the ECU to the OBDII port.

The Vehicle Speed Sensor (labeled as VSS on the diagram) is on the transmission. Not sure what the output signal is for the VSS.

Pin 41 (in the 58-pin-connector) is not used in this application...I don't remember what it is used for.

The "cranking" circuit as TurboCobalt mentioned is a separate circuit in this standalone application. Meaning it is separate from the OEM wiring harness. As you can see on the diagram, it is a simple key switch and start button (and clutch switch) that switches a relay that sends battery power to the starter...very simple.

I am not sure what you are referring to about a terminator resistor. You don't need any resistors in this wiring harness.

Although taking a step back and trying to understand that you are wanting to bench test the ECU, I am not sure if you are going to be able to confirm if everything is working or not. Perhaps there could be a driver or voltage regulator that is not working and I am not sure how you would pick that up unless you are running the engine? Yes it will throw just about every code in the book if you have none of the sensors/solenoids,etc hooked up.

I would just focus your time on getting the harness routed and connected with a fuse/relay box and you can troubleshoot once you know everything is in place. Most likely everything will work fine

[TurboCobalt]

Hello,
I have no knowledge what so ever about this stand alone harness that you are building, I will assume the advice u got on that is right.

Since u asked, I'll talk about how an OEM wires a car.
Powermoding is handled by 2 hard wires mainly. 1 wire is accessory the second is run/crank often labeled R/C. 2 wires, either 0 volts or 12 volts gives u 4 logic states, here's what they are: both lines low, is OFF, car is off, equivalent to ignition key off. Next state on the ignition key tumbler is accessory, that'd when accessory (or called acc sometimes) is high, 12 volt and r/c is low. Third state on the key tumbler is called RUN, this is when both acc and r/c line is high. The fourth state on the ignition is CRANK, that is when r/c is high and acc is low, self explenatory, car cranks. Yes I know things are a lot more complicated, but those are the basics. If I was gonna wire a custom made car I'd replicate this, either with a ignition key tumbler or with switches.

About the can bus, the high speed gmlan is just that, high speed. To make high speed electronics work you need good noise rejection, that's why it's a differential pair configuration and it's a twisted pair. The way can is wired through a car it's kinda like a chain, where each module is a link in the chain. But the beginning and the end links are special, they have termination resistors. The reasoning is complicated, has to do with matching impedance of a transmission line, avoiding standing waves, iada iada. What matters is that your can network has termination resistors. Usually one end is inside the ECM, and in an oem car one more module has the tail end resistor inside some other module, fuel pump for instance. I don't know in the cobalt. So when u make urself a bench harnes u either need to bring in the module that has the termination resistor, or add a resistor like I suggested.

Can u get away without twisting the can wires, sure, probably, maybe, but I've had this bite me before and I won't make the mistake again. Can u make it work without a termination resistor? Maybe, don't know, but I know I've needed one in the past for bench harnesses to work, otherwise the modules won't talk right.
Ur custom harness doesn't have a termination resistor probably cause it has the other module that has the termination resistor, if it doesn't I'd be surprised if ur obd port works.

Hope some of this helps.
Just curious, u paid for someone to give u a schematic? Or did u buy an actual harness?

[TurboCobalt]

That was a ton of writing on a smart phone, I really hope it helps someone, also hope it's all correct, lol, but at least that's my understanding of vehicle electronics.

Turbo wood I won't be around my laptop for another week, but I'll give u exact pin numbers then.

[TurboWood]

You guys are awesome. If nothing else this kit car has exposed me to some of the more helpful forums around (the other being USA7s).

What I bought was a wiring diagram (schematic) and I'm separately buying the harness/connectors/etc. The diagram is from Scott at modernkitcar.com which eliminates everything not needed by the PCM. It does look like I need to do some learning on the vehicle speed sensor and termination resistor.

*edit* Would it be reasonable to assume the termination resistor is in the ODBII cable or computer connected to it?

Daniel

[TurboCobalt]

An obd diagnostics tool, or hptuners in this case, does not have one of these termination resistors. These Are needed for the can bus to work, so you don't want to put them on a removable device. I might be able to figure out which modules have them in about a week when I get back to my laptop.
Don't get caught up with this little detail, this is only for the bench harness, odds are the advice you got from Scott was what u needed to get ur car going.
Sounds like a cool project, some pics would be nice.

[cobaltssoverbooster]

to answer your main question, yes you can bench test an ecu with a power supply.
1) you must trick the power supply to stay on and discharge an output voltage
2) you must wire in the same value fuse for the vehicles ecu main fuse.
3) you will want a voltage regulator, 12v, or a high amp dash pot that will allow you to adjust it to the safe range of 12-13v. (if you use a dash pot with multiple devices for testing make sure that you adjust the input voltage while you are testing those units to keep the voltage the same)
4) the more items you test with the power supply the bigger you need to go. When i did injector testing i powered a megasquirt, j-stim, and a full bank of 8 injectors with a 1200 watt platinum rated power supply. i probably could have gone smaller like 800w but i didnt want to buy a second one.

i have not tested an e69 on the bench so unfortunately i cannot comment further. every one else is already giving you great data though so it shouldn't be to big of a problem.
good luck.

[maccos]

Sorry, I have no knowledge of the said resistors. I assume you are using them to fool the ecu to think that its actually connected to something???

I'd be curious to know what you find out by making a bench test. If I am thinking correctly about what you are attempting, it sounds like you are going to be putting together a large (time-consuming) side project that will have inconclusive results. Not trying to rain on your idea, but I just don't understand the reason. Save some time and wire it up in the car...you'll be that much closer to driving it!

TurboCobalt, thanks for the explanation of the ignition setup on an oem car.

TurboWood-My designed schematic uses a 2 position key switch, when you turn it to the "on" position it sends power to the ECU (the fuel pump primes and a bunch of other electrical gadgetry noises come from the engine)(this also turns on my headlights and running lights). Then you push the clutch pedal in and push and hold the starter button and the engine turns over...let go of button when engine is started, same idea as the OEM setup, just a different approach. You should be able to see how that works by studying the diagram.

[cobaltssoverbooster]

He's trying to flash it so it can be used. IF all you got is the ecu and a harness then all you can do is make a bench rig to fire it up just so you can flash the standalone software into it. Without that test rig all you have is a pile of wires and a door stop.