Long time reader, first time poster. Been looking around on this site to little avail in what step to take to fix my 2005 G35 Sedan. My son was driving it for prom and said after going over a speed bump (slowly, as it is lowered on coilovers) the car tossed up the SLIP and VDC lights and went into 'limp mode'. I had it towed home and it's been sitting for a couple of weeks...

I found the codes following codes while waiting for the tow truck. (I assume some where already there and he hadn't told me the light has been on)
Engine: P0605, P1564, P0011, P0183, P0463
ABS: C1131, C1109
Transmission: P1705

(P0605 OBD-II error code indicates a ROM error in the internal control module of the ECM)

After clearing the codes: The car starts and runs fine, but once it is put into drive and any sort of torque goes to the wheels it goes into limp mode and the P0605 code pops up. Before I go out and try to figure out how to straight replace the ECM, is there anything else I can/should look for? I'm stumped, and would assume that if the ECM has some sort of ROM error, the car wouldn't run... Any assistance is greatly appreciated!!

We did install a radio a few weeks back, I'm 97% sure it was wired up correctly, but saw in the forums that it may be an issue with a ground wire someplace...

 

Yes definitely start with the ground, they almost 100% had the ECM ground unbolted so they could add a ground wire for the new head unit. If it wasn't torqued properly it definitely WILL jiggle loose. It may also have been overtorqued and stripped the threads and was just barely hanging on until just the right chassis vibration wiggled it loose.

Also check the CRANK sensor, sits at the very bottom of where the bellhousing and engine meet, might have bottomed out bad enough to damage the crank sensor. If you look with your phone camera from up behind the lower skid plate you should be able to see it with your camera and a flashlight from under the car. Might be broken off if your son REALLY bottomed it out bad.

P1564 - Cruise control switch, this would also have been unplugged behind the stereo when installing a new head unit.

P0011 - Intake valve control, this can be caused by a damaged crank sensor.

P0183 - Fuel tank temperature, if the ECM ground is wonky it could definitely be misinterpreting other sensor data. This could also be caused by hitting a bump hard and physically bouncing the fuel pump level float hard enough that it damages other components.

P0463 - This can happen when a fuel pump level float ages, mine is currently throwing that code AGAIN, it's sort of a chronic G35 V35 chassis problem however jumping the car could also cause this issue.

For starters have another honest conversation with your son about this "speedbump" and make sure he wasn't downplaying what actually happened. If he hit a speed bump at full speed because he didn't see it then it really changes direction on what/where you would start the troubleshooting compared to if he actually did roll over it slowly.

Quick and easy is looking for a broken crank sensor or harness, followed by pulling the fuel pump to see if the float arm is bound in the upper/lower position or maybe broken past it's stoppers (this would be highly indicative of hitting a speed bump at full speed and not slowly rolling over it), the most difficult and time consuming is definitely taking the center trim off to inspect wiring behind the new head unit.

You should also look under the vehicle for any tell-tale skid marks where it bottomed out, and for bent wheels. Stock 19's will definitely not survive hitting a speed bump fast, they will bend. Stock 18s are still likely to have a bent spot on them.

 

Firstly, Thank you for the response, I have re-read it a number of times as it definitely helped with troubleshooting so far. It has taken me some time to get to this point as don’t have a lot of time to work on the car. With your suggestion, I did lift and look for anything out of place or funky on the car, no significant damage or tell-tale signs of what the issue might have been. Also replaced the crank sensor (no damage) while under there with one I had laying around for the car to throw the same code.

Decided to order an ECM from FS1 (FlagShipOne), which was supposed to be plug and play, no further programming. It, was not… Had it programmed, but the P0605 code came up immediately. I was able to return the ECM and get the money back, nothing but time wasted…

Service Manual EC-102 mentioned addressing the codes as a priority, so, looking at the P0183, I pulled the Fuel pump up to look at it, messed with it some (Forced the float to the middle). Nothing ‘helped’ as expected. Last thing to try for the evening, I unplugged the Sub Fuel Level Sensor on the Driver side and had the kid test it. SLIP and VDC stayed off!! The failure condition was repeatable, plug the Sub Fuel Level Sensor in, Slip Mode 9000, unplugged, purrs like a kitten with no issues. My assumption was to say the Driver side Fuel Level Sensor had a short in it or something causing the ECM to throw the P0605 code. But a replacement only reproduced the failure with the P0605 code. Still need to figure that one out, need to look at the harness, but the car is back on the road with the original ECM. Only out $65 total (so far) for a ‘service call’ from a mobile car tech to program the FS1 ECM.

 

So with the sub pump unplugged you get no codes, but when you plug it in you get P0605?

That's REALLY odd since the fuel float wires to the instrument cluster, not the ECM.