[SammyDog]

All Camaro models from 2016 through 2023 can potentially be affected according to the TSB.

The car affected:

2018 ZL1 Convertible A10, built date 02/2018 with about 7600 miles as I write this.
100% stock, NO LED lights, aftermarket Amp, etc.
No other issues with the car, except for the one mentioned here.
Good battery, 80% life left, >12.5 v
Ref. TSB PIC6397E (preceded by A-D)


Thank you to the ZL1 owner on this forum, who described his own experience with this frustrating issue. He stated that the dealership could not figure out what was going on. A GM factory tech had to be called in. I suppose he is the one who initiated the TSB. So, whoever you are, if you read this, thank you for your work. You solved the problem for me. When someone here solves a problem, please post the solution and don’t let the tread just die off.

However, the story is a little more complicated than as described in the TSB. The stray “feedback” voltage values, yes with a S, can be much lower than 2-3 v.

How to solve:

it is actually easy. The seat heater control module in some cars can be defective. The defective P/N for me was 13511696. It lasted about 5 years. The replacement part for me is 13523758. I opened the defective module. There is no obvious sign of damage on the board, but replacing it, per the TSB, solved the problem. The module costs between $65 and $85, depending on where it comes from. I would not buy a used one on eBay or elsewhere.
Replacing the module is not complicated. It is located under the passenger seat, towards the front. The seat must be removed. To do so there are two Torx 50 bolts at the back. The front of the seat is held place by hooks. There are some videos on YouTube that are quite useful. Whether the seat is a Recaro, or not, the principle is the same.

Move the seat forward, tilt the back forward. Once done, unplug the battery. There is an air bag sensor located inside the seat to the right by the belt. The belt does not need to be removed; the sensor does not need to be unplugged. Unhook the main harness below the seat. It is a two-finger blind operation. Again, refer to the videos. I broke a little piece of it. These plastic connectors/covers are just….

Place some blankets along the door frame and all that. Some metal features under the seat are sharp. Pull the seat half out of the car, with the back of the seat tilted towards the inside of the car. The module is held in place with a small Torx (27?, not sure), a couple of built-in side clips, alignment pins, and two connectors.

Symptoms:

There are many symptoms. Some appear and stay, others are transient.
They can happen just by one or two or in groups, usually a cascade of symptoms.

Assuming that the battery is in good to excellent shape, often the battery will drain to 9.5 volts in less than 48 hours, and it will keep draining. In a few cases, nothing happened for days until the car was awaken, no symptoms no battery drain, but it is rare. They will come back. I also checked the current draw at the battery and have experienced less than 50 mV one time, but also, 120mV or more.

The car can be driven. It never went into limp mode. The CEL will come on often and sometimes it disappears. When cleared, it stays off at times for a while. It never blinked, but at times it lost intensity and faded away! It can stay on for days even when the car is off and appears asleep, which is obviously not. Otherwise, when the engine is running, because the charging circuit is fully loaded at times, the car runs fine. It becomes a problem when it is stopped.

Relays clicking are common. I heard one under the car by the fuel tank. It lasted for a period, then disappeared, and never came back.
The ECM relay K7 will often start clicking, in particular if the voltage drops below 11v, then the throttle body will start clicking with it. The Run/crank relay will often click as well. All this happens when the car engine is off, and semi asleep.

Codes P0685 and P1682 may appear because both circuits (fuse F16 and F40) are not at the same voltage level (5.01 and 5.0 for example). There will be other transient codes at times which ultimately do not mean anything (ABS, transmission controller, radio!!!, and others, -> cleared and in my case disregarded).

Car does not start, nothing, no click, no crank. After pressing the button 3x it usually does (this is not a battery issue, not a starter issue). And the scary one: the engine does not turn off, as in “everything is off”, and the engine keeps running. This is the one that got me fuming. I do not use the car much, so I researched the problem for a while, halfheartedly, knowing that eventually it would get fixed. However, the day the engine could not be turned off, that was it. In case you wonder, either K2 or K7 remained energized, and this is why the engine stayed on. Others must have stayed on as well, like the fuel pump, etc. After pressing 3x on the on/off button, it turned off. It is just a weird feeling when all the lights are off, instrument panel off, and the engine is on.

I started calling the car Christine instead of Nicole.

Temporary fix (none really, but):

Remove fuse F16 and F40 which are located in the front fuse box. No work was done in the fuse box located in the trunk. This is for storing the car until the module is changed. This will preserve the battery.

Here are a few of the stray voltages detected in one test session, with the current equivalent iterated and about right. Obviously it is the current that’s powering the system, not the voltage. I used the famous table to convert based on the fuse size.

Rough figures, after the car was “supposedly” asleep, 20 minutes in:

At F16 (heated seat) .75mV = 160mV, but after F40, its buddy was removed, V = .20mV, STILL POWERED!!!!

F19, airbag, the car is off mind you, 1.35mV = 175mA

F40 (in “pair” with F16, regarding the seat heater module), .35mV = 95mA

F41, the CEL is on of course, because it is all screwed up, .27mV = 17 MA

MAF/O2 sensor circuit (there is the throttle signal): .57mV = 78mA

Etc. there were others. Many more were at zero volts of course.

When the voltmeter is used, wait until the mV reading stabilizes. Like the TSB says, at the fuse, the voltage should go down to zero after a few seconds if unpowered. Not all systems go to sleep right away however, but those voltages are much higher than mV. Just wait 15-20 minutes before testing the fuses.

Two things: if the trunk is opened, make sure you use a screwdriver to close the switch so the light is off and close the doors.

The hood switch will be on. I am not sure how much current it pulls.

After the module was replaced, the first time, the car did not turn on!
Another gremlin due to reconnecting the battery, and letting the ECM know that a module transplant had happened. Press twice on the button, and everything has been fine since. It now needs only one button push to start which is customary. There are no more CEL, codes, relays clicking, and the battery does not drain overnight.

Tool used: A decent DMM, with a good battery (required)

Optional tools:

To check the battery drain, plug DMM in series with the negative of the battery. Additional wires are required. It can be useful in general for battery drain checks, but it is not required here.

PDI CA-60 amp clamp. Optional. Careful because the clamp does not close fully on the fat battery cables of the ZL1. Add another 40 to 50 mA to the value read. It is hard to use because there is not much room in there. Also, this item is pretty jumpy and takes a while to provide a stable reading. Not required here.

Autel MK906BT scanner. I am not a car mechanic, but I own one of those. It is a great scanner because it will read some codes that my cheapo Actron scanners will not. It is also bi-directional, which is a must for some detective work. Here it is not necessary to have one as long as the codes can be detected and cleared another way with a cheaper tool.

[DevilsReject97]

Good information to have, glad you posted it!

[GroundhogSS]

Very good info, thanks. I've had some weird electrical gremlins but none this severe. Still get message to open and close one of the windows, usually the passenger.


After the battery is disconnected, it will always take two pushes on the start button the get the engine running.

[rorr]

Originally Posted by SammyDog

All Camaro models from 2016 through 2023 can potentially be affected according to the TSB.

SammyDog,
Just wanted to say thanks for this post. It helped me immensely. I was having a similar issue with my 2017 2SS Convertible. P069E code, battery being drained overnight, but the car ran perfectly. It wasn't until it got cold here in GA and I went to use my heated seats that I noticed they didn't work. This led me to search for why and I ran across your post. It made perfect sense and I immediately set forth to diagnose my issue according to the GM TSB. I found a reasonably priced new version heated seat module, installed it and my battery draw went away and phantom fuel pump module DTC went away.

Again, thank you for your information and I really appreciate it. My car is back in action and we are a happy Camaro family again.

Sincerely,
Robert

[ChosenM]

Wonderful write up, seat heating module ended up being the issue in the 19' 2SS as well.