I have an 03 G35 automatic, 73K miles. For a few days, I've heard a rattle that comes and goes, only when the engine is on (moving or not, in gear or not). Otherwise everything was normal. Today, after driving to work without incident in a big rainstorm, the following happened on the way home from work:

1. SLIP and VDC lights were on from the moment I turned the car on, and stayed on
2. Shifting was very rough
3. The car sometimes lost power (almost as if the brakes were being applied for a few seconds)
4. The speedometer was at 0 even when the car was moving, and the odometer didn't change
5. Occasionally, the turn signal seemed... weak? The rhythm was off and it seemed kind of dim
6. The rattle continued, no difference from before
7. There were no other electrical or obvious mechanical problems

The SES light did NOT come on. I drove the car straight to my mechanic and left it there.

Oh, and a few days ago, the car was at the shop for an oil change, and they also changed the air filter and cabin air filter. They also tested the battery and found it to be good. The rattle probably started soon after that.

I searched, and although symptoms like these are not unusual, I haven't yet seen this exact combination. Any ideas what could be going on? The rattle sounds to me like it could be bearings that have gone bad, such as on an alternator. (The last time I heard something similar was 30 years ago, and it was a broken water pump.) But I'm not sure how a bad alternator could cause all the other symptoms.

 

Check and clean your ground cable to the battery. Check your brake fluid level.

 

Probably Camshaft sensor bank 1 or 2 are bad, pull error code see what the problem.. I have similar problem as described few years ago and bank 1 sensor was bad, I replaced both while at it....

 

The check engine light isn't on. Would there still be error codes?

 

Judging by your turn signal issue and the dash not working right it sounds very electrical in nature which wouldn't be caused by a bad cam sensor.
Are you sure it's working (turns on when key partially turned?) I would definitely start by going through all the grounds in the FSM.

My guess is the rattle is an unrelated problem, maybe a timing chain tensioner gunked up with oil from sitting (you have low mileage for the year). Try running some seafoam through your oil and see if that makes a difference after this electrical problem is fixed.

 

My mechanic said the car showed a code for a transmission speed sensor. He ordered the sensor and was about to replace it today. However, he drove the car one last time and noticed that it was working fine (VDC/SLIP lights off, speedometer fine). So the best guess is that in the rainstorm, the sensor got shorted.

Of course, I'm a bit worried that this will happen again the next time it rains. Any suggestions? Are there any specific locations that should be waterproof (such as where the sensor leads connect), which we can check to see if the seal is broken or something?

(And the rattle was indeed an unrelated problem - something to do with the exhaust system. I didn't catch the exact explanation. He said it's an easy fix.)

Edited to add: I just looked at my original list of symptoms. The speedometer at 0 and the VDC off both make sense, as do the rough shifting and loss of power. What doesn't make any sense at all is the weak turn signal. Unless some connection related to the turn signal is close to the transmission sensor connection, and water got in so they both got shorted...? Does this provide some clue about where to look?

 

The thing that makes electrical problems hard to figure out is they can trigger false codes: the speed sensor could be working fine but the signal's not getting to the correct computer because of a short or intermittent connection, triggering the code. Maybe the turn signal light being dim could provide a clue but you'd really have to be a wiring expert to make that connection.

Go through and clean all your grounds, trace the wiring back from the speed sensor, hopefully the problem will reveal itself.... You could try spraying various parts of the car with a hose, driving it, repeat until the symptoms trigger again to find the location of the problem if you're certain it's related to the water.

Maybe someone else will have something more concrete. GL.

 

2 people have now told you to check and clean all of your ground connections. It is the first thing I check when faced with electrical issues.

 

Take the battery out and inspect the IPDM for moisture damage. Your front drains may be a little clogged and water spilled into the battery compartment and got the IPDM wet during that big rainstorm, it's got a gasketed cover but sometimes it's not installed correctly and moisture damage is a VERY common problem and you end up with strange intermittent issues exactly like what you're experiencing.

 

Few years back my car would not start, and vdc, brake ,check engine light ect... all came on , read somewhere online clean and lightly sand the metal frame and the 4 screws that held ECM unit contact to frame of car, after that car run fine ....

 

^^^ That is cleaning one of your grounds. At the age of the car it's a good preventative maintenance idea IMO to go through and do this BEFORE your car decides to die on your because of a poor electrical contact.

 

Thanks, everyone. Looks like I need to figure out where the IPDM and ECM are. Some casual googling leads to this helpful blog post:

http://jfbreton.blogspot.com/2015/05...ssue-what.html

His symptoms were a bit different from mine, but close enough that I suspect a wet IPDM is the culprit. Now that I have the car back I'll poke around in there and see if the battery compartment drain hole is clogged.