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I picked this car and P18C4 code (gear selector sensor) was disclosed to me by the seller, he said it was cleared and had not came back, well it did come back on me after some time. I disconnected the battery for a reset and all was good for a few weeks and then it returned again. I cleared the codes with my code reader this time to return functionality.
I really need to get this fixed asap for California smog check and wrapping up with the DMV. When taking it in for further diagnosis will I need to wait for the CEL and loss of functions (gear indicator, rev match, cameras) to return or are the codes stored even though it all looks good at the moment...functions working and no CEL?
Anything else I can try myself, all I have been able to do is get my hand up there and wiggle the wires by the sensor, looks like a big job if it does needs replacement.
Last edited by boraxman; Jun 19, 2023 at 07:15 AM.
As for California emissions, it looks like I can pass if I get 15 warm-up cycles and 200 miles without the CEL returning. I can always deal with the underlying issue later as once CEL cleared as it doesn't seem come back for a good long while.
With my luck it will come back just before I hit the required cycles. Fun stuff!
Since the problem is intermittent the first thing I would do is disconnect the sensor and spray contact cleaner in both halves of the connector (harness side and sensor side). The problem could be with the sensor or at the other end of the wiring harness at the ECM (bad ECM or poor connection) but I suspect the transmission end is where the connections have a chance to be more exposed to dirt and moisture. When diagnosing electrical faults the first thing you need to do is ensure all electrical connections are clean and making good contact including ground connections.
The diagnostic table for P18C4 shows that you are concerned about Gear Position Signal 1 being shorted to ground so also check for damage to the wiring.
Unfortunately there's no way getting to the sensor/plug on the trans end. Will try poking around on the ECM side a bit. Right now getting to pass emissions is the priority - hoping I can get the warm-up and miles cycles in before the CEL returns.
I picked this car and P18C4 code (gear selector sensor) was disclosed to me by the seller, he said it was cleared and had not came back, well it did come back on me after some time. I disconnected the battery for a reset and all was good for a few weeks and then it returned again. I cleared the codes with my code reader this time to return functionality.
I really need to get this fixed asap for California smog check and wrapping up with the DMV. When taking it in for further diagnosis will I need to wait for the CEL and loss of functions (gear indicator, rev match, cameras) to return or are the codes stored even though it all looks good at the moment...functions working and no CEL?
Anything else I can try myself, all I have been able to do is get my hand up there and wiggle the wires by the sensor, looks like a big job if it does needs replacement.
This exact code popped up on my 2014 C7 Z51 Manual Trans.
Had CEL, loss function of rev match, and backup camera wouldn’t pop up if the screen was in the down position (would still work if screen was in the up position), also gear was not populating on the instrument cluster. The car drove fine besides that. I would delete the code and it would return almost instantly.
I found another thread on here of someone else having the exact same issue on their Z06. The dealership ended up replacing the gear position sensor on their vehicle. https://www.corvetteforum.com/forums...ay-be-bad.html
I have access to a 2 post lift. So I ended up being able to fit my hand up there and was able to remove the connector to the gear position sensor. I verified that the connector was in good condition. So I proceeded to check for power and ground and found that source voltages were good and ground was good. Which at that point I went ahead called it as the gear position sensor was bad.
The sensor is extremely difficult to get to and my forearms were all banged up after I replaced the sensor but it was better than dropping the whole rear subframe and trans. It’s totally possible to get it replaced with the right tools in about an hour or two (also 2 post lift helped a ton). The sensor has 4 8mm bolts that hold it down. You also have to replace the gasket that is underneath the sensor as well. Once you get the bolts out, the sensor will be pretty snug to the transmission. I ended up using a medium size snap on pick to pry the sensor up. After I did that, I heard the pressure release from the top of the transmission and I was able to remove the sensor.
Installing was a bit tricky, but I just put the 2 bolts through the front two holes of the sensor with the gasket mated as well and was able to carefully bolt it up to the transmission.
Once it was all done I deleted the code and everything started working again! I didn’t reprogram sensor like the post stated. Everything was working great after the install.
Just a heads up the sensor is on back order with no ETA everywhere. I got really lucky and found 1 available on Rockauto after checking the site everyday. I also called several dealerships and everyone said it was on back order with no ETA.
These are the parts with part numbers that you will need if your gear position sensor is bad. 24283436 :SL-N-SENSOR
19330912 :SL-N-SEAL
^^^^^^ Wow - Thats some great info! I just dont see how you could have possibly got in there. My hands aren't so large and no matter how hard I tried I couldnt hardly touch it let alone unplug or get a wrench on it.
I wonder if the dimensions are different on the Z06 or what?...I know the trans is a different part number than a Z51 but are the cases identical? Hmmm
Well Im really close to the required warm up cycles and the 200 miles since clearing codes for smog test, so if CEL doesnt return on the next couple of drives Im going to try testing.
^^^^^^ Wow - Thats some great info! I just dont see how you could have possibly got in there. My hands aren't so large and no matter how hard I tried I couldnt hardly touch it let alone unplug or get a wrench on it.
I wonder if the dimensions are different on the Z06 or what?...I know the trans is a different part number than a Z51 but are the cases identical? Hmmm
Well Im really close to the required warm up cycles and the 200 miles since clearing codes for smog test, so if CEL doesnt return on the next couple of drives Im going to try testing.
That’s a good point, not sure if they are the same dimensions.
It is a tight fit and I think that maybe removing the mufflers then you should have a little bit more room. I ended up using a 90 degree pick to unlatch the connector with one hand and used my other hand to pull up on the connector, almost like hugging the transmission. I used a 1/4” flex head ratchet and a stubby 8mm socket to remove the bolts for the sensor.
Hopefully it works out for you and you can pass smog!
I'm having this exact same issue on a 2015 Z51, it happened a few times last summer but cleared itself up after a few restarts. This year it's returned and gotten progressively worse. Short trips are usually ok, but any drive over 15 minutes or so is guaranteed to result in this error thrown.
It sounds like the sensor is probably bad, but I do have an original OEM battery that seems to be working just fine, but I'm wondering if it's worth proactively replacing that to see if it helps before scheduling an (expensive) appointment with a dealer who might want to drop the transmission to replace this... if they can even get the part?
Mine seems to have gone away since disconnecting and reconnecting the battery - hasn't returned in 1k miles. Seems a poster above managed to get to and replace his sensor on z51 without ripping the car apart.. not happing on a Z06.
P18C4 Code on 2016 Z06
