Crav3

iTrader: (1)

I have a 2008 ppontiac G5 GT and it will not start. I get the antitheft icon on the dash. I had a tech program my key and apparently it worked. Then the anti theft icon came on again causing no start.

The car already has a new ignition switch abd lock. When trying to connect to OBD2 scan tools say no link and GM MDI says cannot connect to engine control module.

We used a tech2 to scan for codes and we get "lost communication with engine control module" "lost communication with body control module" and "lost communication with traction control module/TCS". Tried erasing the codes but the wont erase.

Yesterday I replaced the ecu and I can now hear the fuel pump and throttle adjust. But still get the same error with scan tools. The bcm is good because everything inside the car works fine even the dash and gauges. It just wont connect to a scan tool.

When we try to program my vin into the ecm it says it cannot connect. Any idea what it might be? We have checked grounds, fuses, even all the module connectors and they all seem fine. I am close to giving up and selling the car to the junkyard :/

Thanks for reading and for any info

Snail_SS

iTrader: (3)

Sounds to me it's something with the harness including connectors and wires. Not necessarily close to the connector for the wires it could be anywhere

Crav3

iTrader: (1)

The connector does sit a little funny. And do ypu know what wires are the grounds for the ecm? There is not ground on the ecm itself but the tcm has ground on it

Snail_SS

iTrader: (3)

Not necessarily it has to be a ground maybe a wire got cut or is loose or it shorting out

ItalianJoe1

iTrader: (10)

Sounds like the CAN harness could be damaged or unplugged, follow the normal diagnostics for loss of communications and go from there. Check for continuity on the CAN-BUS pair between the suspect modules, look for signs of contamination or corrosion in the connectors, or bent/damaged pins on the module or connector itself. Something isn't getting a clean signal if they can't talk to each other but are individually working.

Did it just randomly stop starting or was this issue after some other work was done?

Crav3

iTrader: (1)

I did try a test on pin 6 and pin 14 of the OBD2 plug that are gmlan high and low respectively.

I got a reading of 120 ohms with ecm unpluged like it should. Then it told me to unplug the eps and it should be infinite ohms, but idk how to measure for infinite ohms lol. That determines if there is a short in the canbus harness. But cant find many info on how to diagnose the problem. Most people on the internet end up taking the car to the stealership.

I cant find any diagrams either. Anyone got access to alldata?

T-fog

Usually to get the infinite reading it won't have a reading on your meter or it will have a 0 with a line through it.

Snail_SS

iTrader: (3)

Yeah the voltmeter has a sign for infinite ohms can't remember what it is tho

Crav3

iTrader: (1)

I check the wires for the high and low canbus signal wires by the ecu connector and I dont get a reading. But inside I get 120 ohms. I think ill try it again later to make sure. And I kept try all tge setting on the voltage meter and dont get a reading for infinite

T-fog

You keep your meter in the ohms scale, If your screen goes blank or you get a zero with a line through it then you have a reading of infinite ohms.

Sorry if my last post wasn't clear

ItalianJoe1

iTrader: (10)

The infinite is whatever it shows when you turn the meter on and the probes aren't touching anything. That's an open circuit (infinite resistance).

If you're not seeing the same 120ohms on the pins at the ecu connector, there's a break somewhere in the harness.

Crav3

iTrader: (1)

Tomorrow im going to look thru the harness and see if there is a break anywhere. Can I bypass them from the obd connector pins to the connector?

Update: I figured it out after going through the wiring harness. The abs module is broken. Idk how it happened but that is where the problem is.

I bought one off an 09 HHR but the pins are different. I cant find anything for an ESC module for an 08 g5. The part number off the module doesnt come up on google and called autoparts stores with no luck. Will have to check the dealer tomorrow. Thinking its gone be abput $500 :/

ItalianJoe1

iTrader: (10)

There's a G5 at the local u-pull-it, what's the part #? I could stop in and if it's what you need I'm sure it would be under $200.

Crav3

iTrader: (1)

I looked through every junkyard in the area and it has to be a g5 gt and specifically a 2008 model. Apparently the modules are different between all disc brakes and front discs, rear drums. I found it for $281 at rockauto and might get it there since at the dealer it's $700

Snail_SS

iTrader: (3)

I saw a GT at a yunkyard but it was pretty gutted. Last time I went

Crav3

iTrader: (1)

Got the part at rockauto a while back and the car cranked but wpuldnt start. Turns out the engine was shot so I replaced it with a 2.4 off a 2012 malibu and not it starts but after 3 seconds it dies. I think its the key that needs programed but everyone that has come to see the car cant get it programed.

Im thia close to torching the car now for sure lol