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Problems/Service/RepairsIf you have a problem with your HHR, want a tip on repairing or performing a particular service to you HHR here is the place to post!
Yesterday afternoon went to start the car. 85F out, car in direct sun with windows up.
Interior hot. How hot don't know .
Turn key acted like a dead battery, new battery installed 3 weeks ago.
First looked at radio to see if the face changed, it didn't. That's the first sign of a bad battery.
Used my Lithium Ion jumper pack and the car started.
Check engine and security light on the dash lit.
Drove the car 2 miles and the DIC dropped out with info and the trans started shifting hard and no power steering.
Park the car and the next morning used my BAFX OBD2 with my phone to pull codes.
It's now 65 F at 7 am.
Only code U0100 = No communication with ECM. But the car started with no external help.
Only two things lit were security and check engine light.
Pulled the 50 amp Maxi fuse at the back to reset the BCM. Now when started the only thing that was on was the check engine light and the code U0100.
Pulled the negative cable on battery and let sit 20 minutes.
Reconnected the battery and started the car. Check engine light off and the only thing on the DIC was no tire pressure. Drove 1/4 mile and that woke up.
Has been starting normal ever since.
Will it fail again, don't know ?
So why do these cars get brain farts with the controllers and have to be reset by disconnecting the battery ?
Tried to Google this and really can't find an answer to my question.
I did find something about reflashing the BCM but that's a dealer thing. And you know going to a dealer is a very big crap shoot on this.
U0100 refers to the ECM losing contact on the serial data lines. The Book has contradictory info on the code; at one point it says it is the ECM at another it says the TCM.
Nothing to do with the BCM.
I would suspect either a loose wire or connector. The new battery would lead me to triple check the battery connections.
Thanks for that info Don.
I don't have a scan tool to see codes like U100-U02FF or anything else.
It does say don't just replace an ECM, BCM or TCM.
It did say something that reflected towards the TCM as the trans did shift hard until I did a "reset".
U0100 is a very wide code indeed.
I did find something about the TCM as to adding an external ground to it's case.
Would this help a U0100 code ? I don't know, as this problem looks to be random at this point.
All connections at the battery are clean and tight, just to give you that info.
Since this happened, have you had to jump start the vehicle anymore times?
No. Have started the car about 10 times during the course of the day and no issues.
Carry my jumper pack with me if it does happen again.
Also a 10mm socket, 6" extension and ratchet to unhook negative battery cable if needed.
Ok, the jump starting seems to have been a separate issue. Everything you posted leads me to believe that you have a TCM going out. Never heard of the ground wire hack, but trying that is cheaper than a TCM, which replacing may or may not fix your issue. As donbrew said the BCM is not the issue here. It's also possible you won't see the issue again.
Today is 6/26 don't have any problems.
Just for the heck of it I'll hook up an extra ground to the TCM.
As ChevyMgr has said: "Everything you posted leads me to believe that you have a TCM going out." When done will give a picture of it. Again will it help. "I don't know?"
At least one of the pins in the TCM connector goes directly to ground. So I don't know how it could help, only harm if someone is careless and shorts the wire to bat.
Update again
Yesterday very warm day. Used car a few times with no issue. Late in day went to a store again, check engine light came on.
DIC showed warnings, trans started to shift hard, no speedo.
Came home shut off car and tried to restart. It didn't.
This morning it's cool out.
New codes have shown up.
U0100 - original code
U0073 - new code
Both are for CAN bus A
U0101 - TCM loss of communication.
Just to see I turned the key and it started.
Check engine and security light on while running, cleared codes while it ran. Felt a change like a "bump" in RPM for moment and engine still ran. Maybe for a millisecond.
I have not tried the extra ground wire to the TCM yet, but now I will.
I also think it's temperature related. But the problem it still a random thing.
I also will pull the connector to the TCM and have a look see.
Any thoughts from you Don ?
Or maybe Chevy Manager ?
I just found this video. The guy's problem not might be mine, but he goes thru how he troubleshooted the CAN bus wires.
Since we have been hearing about oil in connectors lately; I would look at the connector on the trans. Specifically the tan and tan/black wires.
Ground for the TCM is on pin 49 (blk/wht) it goes directly to a splice that goes to the ground on top of the trans then to the rad support.
As far as I can figure you have an intermittent short to ground, or a loose pin on one of the CAN busses. There are 2; high speed and low speed.
This is one that a GM tech would start expecting you to pay for new modules, one at a time, even though the book specifically say "don't replace a module based on this information".
The reason the pair don't always show together is that the inhibit each other and they won't show as current only as history. As soon as the U0073 pops up the TCM stops working and the trans has to control itself (like open loop).
This is all guess work, since it is on the CANbus and the book is sketchy on it. Your vid is pretty on point to identify the point of interest.
06-24-2019, 12:22 PM
