2009 Equinox electrically dead

[Will_K]

Hello everybody. A few weeks ago I bought a 2009 Equinox mechanics special. When I went to the dealership who was selling the vehicle wholesale, the sales guy had the car started when I got there and it was overheating. A quick oil cap inspection showed a likely bad head gasket. I got a discount and trailered it home. The intent is to have this car ready for a child's first car on her 16th birthday a month from now.

The mechanical part of the engine was no problem. I replaced the head gasket and most everything else that needs replacement on a car with 176k miles while I was in there. I drove the car to work a few days with no issues.

The other problem was that the car came with an aftermarket car alarm system, and at the initial test drive it was going off non-stop. That was addressed by unplugging the horn. Removing this system lead to a no crank issue that I haven't figured out.

My assumption was something got cut that I couldn't find, so I replaced the dashboard wiring harness, but the same thing still happened. Turning the ignition key to start resulted in cutting off power to everything that gets power when you turn ignition to on. But that's not quite the problem I need to deal with now.

For whatever reason, this turns into a case study in why you disconnect the battery negative cable. What I had been doing is disconnecting battery positive because it was more convenient to drive the nut on the battery cable connection to the terminal. What happened next is that whatever I was doing, the ECU managed to come into contact with battery positive while the negative cable was connected. A sound resembling a bottle rocket whistle then pop followed and a small puff of smoke then nothing.

Where I'm at, I have no electrical power to anything. No dashboard lights or displays, no dome light when the door opens, nothing.

I've checked all the fuses and none are blown, all have continuity. Battery is charged. I can read 12 volts at every fuse with a multimeter to the battery negative. There's continuity to the negative battery terminal from the engine block and body.

I've run out of logical explanations to look for, do you have any suggestions? I'd think this was something like a blown fusable link but I can't see anything like that, and if that was the problem it would seem as though I'd have had no continuity to the body or engine.

 

[Hey Vern!]

In regards to the alarm, many come with a starter disconnect. You may have removed the connection to the starter when you removed the alarm?
In regards to the ECU bottle rocket pop, was the positive cable disconnected and it somehow maintained current to the ecu? where did the pop sound come from? under the hood, in the passenger compartment....?

 

[Will_K]

Negative cable connected, positive cable disconnected, so the positive terminal contacted the metal case of the ECU and had a path through ground to the negative battery terminal. I was doing something in the engine compartment and knocked the ECU off of whatever it was sitting on - probably the fuse box cover - and it contacted the metal bottom.

The alarm was a pain in the ass. Unlike most videos it didn't have a seperate starter disconnect. That seemed to have been integral to the alarm brain. I removed all modules and got no crank, I reconnected a couple modules and I was able to start. Then I just started removing spliced in wires and never found one where a wire was cut to connect in the alarm system.

My thought was that the alarm system was probably actually put in as an attempt at a cheap fix to a BCM problem. But I can't test any theory including that one until I solve the problem of no electrical power to anything.

 

[Hey Vern!]

The sound you described makes me think the capacitor exploded on the ECU board. Maybe it fried the BCM in the process. I'll see if I can find a schematic.

 

[Will_K]

Update. I resolved the no power situation. The middle connector for the engine compartment fuse block wasn't fully seated.

Now I'm down to the nocrank nostart issue and my scanners are not able to communicate.

I do have an ecu and bcm from another vehicle if I can figure out how to communicate with them. I think I can reprogram the vin but I have to figure out the communication problem.

 

[Will_K]

Further update. The engine control module and either the rear axle module (on AWD vehicles) or a diagnostic link resister (on FWD vehicles) provide 120 ohms resistance each at either end of the CAN network, and at the diagnostic test connector you should get 60 ohms as a result of the two resistors in parallel. I haven't actually located the diagnostic link resistor, but measurements point to it as a problem which may be causing my no communication problem with the scanners. The DTC reads open with the PCM disconnected and 120 ohms with the PCM connected, and the PCM reads 120 ohms.

I'm still going to have another problem to diagnose after I fix the resistor based on the fact I had a problem before.

For reasons I can't explain, I'm getting an instrument panel error code now stating that the hood is open - this wasn't present before. I don't have a hood latch sensor present, and it looks as though a mercury switch was added near the hinge as part of the aftermarket alarm.

I made a quick run to the junk yard at lunch thinking I could easily find and grab a data link resistor off the rear suspension module... only to find that I couldn't find it? The description on the wiring diagram states it's near the X400 connector. I think I was looking for it on the axle side of it and not the other side, but the harness looks like it disappears behind the fuel tank or something.

It could also be a broken connection somewhere between the DLR and the BCM - or for that matter it could be a connection broken somewhere else between the DLC. But If I could grab that resistor quick I'd rather have it on hand for this evening's diagnostic efforts.

 

[Will_K]

I'll just log my progress.

Yesterday I went through some mostly futile diagnostic exercises because I was running out of ideas. I tried swapping back in my dashboard harness to see if anything was different. It didn't really change much, but in the process I discovered one connector I missed on the electric steering module.

With that connector in place, now I get communication with all modules except for the TCU and PCM. The resistance check shows 120 ohms with the PCM disconnected so the rear resistor is showing up.

As a side note, I have the fancy tablet T8 scan tool thing from harbor freight. I figured out how to get to the other modules in spite of no communication to the PCM. I have a new GM key fob I had bought and which they said I'd have to bring in the car so they could program it for $120. I was able to program the key fob myself.

Today at lunch I thought I'd run to the junkyard and grab a TCM. This same tablet gives me the ability to reprogram vin numbers in modules (I believe - I found the functionality snooping around on another Jeep vehicle I have) I thought that it would be easy, it's just 3 screws right?

Well, it's under the battery tray support bracket and one of the brackets holding that onto the structure is packaged so you can only get a box wrench on it. Great. So I had to work around that bracket. And then the screws for the TCU are 12 mm socket screws, and for the most part everything is otherwise either 13 mm or 10 mm, so I tried 13 mm and may have rounded some corners, so 1 screw wouldn't come off.

I didn't have enough time to try another car, and the thinking was if I had the time I'd grab an engine harness - that obviously didn't happen but if I can get back before they crush out that row maybe I'll have a chance at having a head start on the removal. I just need to come back with a 13 mm box wrench apparently.

 

[Will_K]

PEBKAC error. I didn't have a connector properly seated on the main fuse block and that resulted in the engine control module and trans control module not getting power.

So now I have (or had) power to both and could read them on my scan tool.

Apparently however when I bought a new key and thought that I got the computer to learn the new key, I was going through the motions and doing. So when the engine and trans modules were back online and I tried to use my key they hadn't learned, I seem to have triggered the immobilizer.

Now I have no electrical power. Only the check engine light is on. Nothing else on the IP. No lock symbol. No data. No dome lights. The key is locked into the ignition.

I charged the battery overnight and didn't disconnect cables until this morning, I am hoping it resets after sitting a while because I can't see anything else I can try.

 

[Will_K]

I'm going to close this out with a final update.

Next suspect was a connection on the engine fuse block. I briefly got back interior lights as I fiddled with connectors. But I did so with the box not installed. Thinking I had one problem solved, I disconnected the use block, installed the box and reconnected. And I was back to no power.

Among diagnostics I observed some places that should measure 12v were measuring 2v. Some measures 12v. Not until yesterday did I put together 2 and 2. This was due to a good ground on the engine and a bad connection to the body ground. I realized the 2v readings came from the interior and the 12v readings came from the engine compartment.

I had also swapped fuse blocks before I found the ground problem. This may be why when I had power back my no start problem was also solved.

The car is now back to being drivable.

 

[Hey Vern!]

Will, I commend you for sticking with it and figuring it out.

 

[bagbyjw]

My head hurts from reading and trying to follow all of this