2003 G35 nothing aftermarket... driving fine as usual and stop to get coffee on the way to work and when I come out it will not start. Turned over great, just wouldn't start. Got the code reader, would not link with the car. I checked fuses on back panel and found #82, the ECM relay fuse, to be blown. Replaced, car started. I now have a P0031 code. After reading about P0031, I started wondering if it could this have anything to do with the blown fuse?

Any help appreciated -- again, car is running great... just trying to figure out what happened and if P0031 is connected.

 

Maybe/maybe not, that code is for low amperage to bank 1 a/f heater sensor. Something, could have shorted and sent a power surge through the system. I'd read the fsm check the sensor and then the wiring at the ecu. The 31 could be an after affect of whatever blew the relay fuse or maybe have been the cause if it shorted to ground.

 

UPDATE!!! Drove 9 miles to work this morning just fine. Went out for lunch... the car dies while waiting at a draw bridge. Lots of fun....

Read the codes and now I have P0037 in addition to the original P0031. About to go research it now...

 

Also check your ground connections, a slightly corroded ground, intermittently open ground circuit arcing can blow that fuse as well as positive to ground (or just a current leak, not always a hot to ground fault).

Either way I'd start looking for some damaged or corroded wiring.

 

That's for the post CAT heated oxygen sensor on the same side. You definitely have something causing a current draw on the system. I would seriously consider parking the car until you get it resolved. Check your grounds, inspect the wiring going to the sensors, ECM, etc...

 

Don't mean to sound ignorant... but when you say check your ground connections... you mean the one off the battery only?? it was a little corroded and I wire brushed it... how would I check grounds in other places? I have no idea how to check for a current leak!

 

so I shouldn't just go buy another sensor and replace it... correct?

maybe the wire/harness is melted or something... I'll have to check tonight.

** Hope I make it home! (I just went out and checked... it started fine, which is weird considering it would not start at lunch)

 

Yea, don't go throwing parts at it, I mean theoretically it could all be coincidence. But, when you have a blown fuse there is usually a reason for it. I would inspect that side of the wiring harness and look for frayed wires and things like that. Also, the codes you have mention specifically about low amperage, so it's probably an electrical problem.

Read the FSM it tells you what wires to check on the ECU and what not. If you're not comfortable learning, lack of experience/time, or anything I would bring it to a place. You don't want to end up messing up the ECU and if anything goes bad in that ECU you have to replace the whole thing.

Also, DO NOT put a bigger fuse in there if it blows again.

 

10-4, thanks for the kind advice.. do you think a bad battery could be the root cause if this? My battery sucks... def need a new one. it causing a lot of corrosion that has to be scraped every week or so.

 

Actually the battery might not be the root cause, slow drains on the electrical system cause a lot of corrosion on the battery (also causes the fuse to blow when amp draw exceeds the overcurrent protection (fuse size). What I meant earlier was check ALL the grounds, usually from the battery there will be two, the big fuse box next to the battery might have a supplemental one also. Clean the metal to metal parts with a wire brush and apply an anti oxidation grease (de-ox) to both sides of the metal before tightening.

Definitely sounds like you have some frayed wiring or burned/scorched/damaged insulation on the wires somewhere.

 

thanks for the insight... I'll give all that a check. Here's how my battery has been acting, all within the last 3-4 weeks. My horn will get quieter every time I lock and unlock the doors with my key, the interior lights will get dimmer... until I disconnect the battery terminals and wire brush. At this point, the car will not start due to the battery. Then it starts fine once I clean the terminals of all the corrosion.

 

It's possible the battery IS the root of the problem. Our cars can pop up all kinds of electrical issues when the battery starts dying. Sounds like with your other issues it's started a slow death so I'd replace the battery if it's over 4 years old. You can take it to a local auto parts store to be tested, hell even WalMart will test them.

 

Or try another battery if you own multiple vehicles with the same battery type!

 

Your battery does a lot more than start the car. It also helps protects against surges and stabilize the voltage. If it's causing corrosion that often it should have been replaced right away. If you have AAA call them, they'll come out, test the system, and sell you a battery cheaper (if you're a member). I've bought all of my batteries from them over the past few years.

There are some body grounds that you should also check. I don't know where they are off the top of my head.

Start with the battery and then move on from there. If you have a multimeter it should read about 12.6 with the car off. Then turn the car on, head lights, a/c, etc... and the voltage should be slightly over 13v. That will show if your alternator is also charging the battery correctly. You could still have some bad cells, so you want to test them if possible.

I'd look into fixing the codes you have after you get a new battery.

 

If the battery has been corroding for a long time (a year) then it's pretty much shot regardless, the most common reason I've seen for significant battery corrosion that required cleaning was a slow drain on the battery that required the starter to work at full capacity for a short while every day to recharge the depleted system. There is a lot of extra heat generated from the cells during rapid charging from the alternator, it normally off-gasses a VERY SLIGHT amount when it does this which reacts with the differing metals on the terminal and lugs and causes a small burst of electrolysis corrosion, also sometimes the battery electrolyte can boil past the terminals making the problem even worse. If this only happens rarely (needed 1 jump start because the headlights got left on) then it's not an issue as long as the battery did not sit fully discharged for more than a day or so. Permanent damage to the dissimilar metal plates that makes up the cell will happen if it sits fully discharged for long as they achieve a greater homogeneous state than they originally were, this is also why batteries eventually "wear out", the dissimilar metals are always trying to achieve a homogeneous state by passing electrons from one plate to the other until they are literally the same metal, eventually this WILL happen regardless of the state of charge of the battery (why you change your battery every 5 years). Eventually the battery will fail to the point that regardless of how much charge you put into it the condition of the electrolyte has degraded and picked up significant amounts of the metal decaying off the plates and the electrolyte itself has become conductive to the point that the plates transfer electrons directly through it (normally the pure distilled water in each cell is an electrical insulator to dissipate HEAT and PREVENT the transfer of electrons from one plate to the other inside each cell). The battery will then decay VERY quickly and you will need to remove corrosion from the terminals each week, it's best to just let a battery like that die, don't even bother wasting electricity trying to charge it.

Anything on the vehicle CAN cause a slow drain, but starting with the big red flag item like the SES light being on is the best place to start. If you battery is older than 5 years, even if it DOES pass a specific gravity test (where they suck up the liquid to test electrolyte inside the cells) it's still wise to replace it during these summer months rather than waiting for the vehicle to not start in the snow or **** winter weather.

Every circuit on the vehicle can be tested for a drain by process of using a megohmeter set on the 50v scale, this is an INCREDIBLY time consuming process however and I've only done it on vehicles a couple times because it's such a pain (restoring classics).

Sorry that got a little long-winded Sometimes it helps to know the how's and why's to certain things though, little details paint a big picture.