02 GT throwing several codes, #8 fuse

[Tripoli]

02 GT throwing several codes, #8 fuse - UPDATED 3-7-2008

Recently, I was having issues with the car running smoothly and code P0340 came on (Camshaft Position Sensor circuit fault). After reading around on the forums, most people agreed that my alternator was going bad. I tested the battery voltage while the car was running, and it was at 12.8 volts. I also tested the sensor, which seems to be working fine. So, yesterday I replaced the alternator with a rebuilt one from Ford. Everything seemed fine for a few minutes, then the SES light came back on and the engine starting running rough again. I pulled the codes and this time I get 4 codes: P0135, P0155, P0443, & P1451.

After searching the forums, it seemed obvious that Fuse #8 under the dash was toast. Sure enough, it was. I popped a new one in and fired her up. After a minute or so, she started running rough again and the SES light popped back on.

The only obvious damage to any wiring related to this fuse is the driver's side upstream O2 sensor connector. A couple years ago, it came loose and melted the outside of the connector when it touched my header. This never threw a code, and has never been a problem for the past two years, nor have I done any work recently around that area, so I find it highly unlikely that this is where my problem lies.

I'm out of ideas at this point and I badly need some help figuring this out. I've read every post I can find about this issue, including several of svttech76's threads and I can't find the problem. I'm open to trying to further diagnose this problem on my own, but I don't really know much about using a multimeter, though I do own one. Any help is greatly appreciated.

 

[Mike97gt]

Recently, I was having issues with the car running smoothly and code P0340 came on (Camshaft Position Sensor circuit fault). After reading around on the forums, most people agreed that my alternator was going bad. I tested the battery voltage while the car was running, and it was at 12.8 volts. I also tested the sensor, which seems to be working fine. So, yesterday I replaced the alternator with a rebuilt one from Ford. Everything seemed fine for a few minutes, then the SES light came back on and the engine starting running rough again. I pulled the codes and this time I get 4 codes: P0135, P0155, P0443, & P1451.

After searching the forums, it seemed obvious that Fuse #8 under the dash was toast. Sure enough, it was. I popped a new one in and fired her up. After a minute or so, she started running rough again and the SES light popped back on.

The only obvious damage to any wiring related to this fuse is the driver's side upstream O2 sensor connector. A couple years ago, it came loose and melted the outside of the connector when it touched my header. This never threw a code, and has never been a problem for the past two years, nor have I done any work recently around that area, so I find it highly unlikely that this is where my problem lies.

I'm out of ideas at this point and I badly need some help figuring this out. I've read every post I can find about this issue, including several of svttech76's threads and I can't find the problem. I'm open to trying to further diagnose this problem on my own, but I don't really know much about using a multimeter, though I do own one. Any help is greatly appreciated.

Repair that damaged wiring you found, The melted wiring may have just started to short after all this time. Maybe there was just enough insulation between the wires to keep it from shorting when it first melted but over time a short devloped. You may also have to replace the sensor.

 

[Tripoli]

Well, I cut out the melted connector and spliced the wires together. Fired her up and let her run for a couple minutes, and all seemed well. Turned her off and checked the fuse and it was fine. Drove her 10 miles home, still running fine, no SES. Fired her up this morning, SES is back on. Same set of codes.

 

[Robs96]

I'm too lazy to look it up. What were the other codes? Also, make sure that splice is solid and didn't come loose.

 

[Mike97gt]

I'm too lazy to look it up. What were the other codes? Also, make sure that splice is solid and didn't come loose.

I agree check the splices and check of other damage up the harness.

The problem changed once you cut the melted harness out it went from popping fases to not popping fuses right?? Well you may also have a intermittent short in that circuit heater in the 02 sensor with the melted harness.

The change in the symptoms shows you are in the right area.

 

[Tripoli]

Well, I tried to do a little more troubleshooting today. I did my best to look at all the wires going to the O2s, and everything, including the new splices, looks fine.

I thought I'd try a different approach, so I installed a new fuse and fired her up. I stared at the fuse while I let the car idle for 3-4 minutes. Turned the car off. Fuse was fine. Turned the car back on and let her idle for a few minutes, fuse didn't pop. By now the car's almost completely warm. I started giving her a little gas, revving up to about 3,000 RPM and letting off. After maybe 15 seconds of playing with the throttle, the fuse popped. Turned the car off, replaced the fuse, then fired her back up without resetting the computer. No SES light, fuse is fine. Let her idle a good 7-8 minutes, watching the fuse the whole time...never popped. Finally tried revving the motor a little...fuse popped, SES light came on. Turned her off, replaced fuse, didn't reset computer just like last time, then started turning ignition key, fuse popped as soon as the key hit RUN, before I even got power to the starter. I reset the computer this time, replaced the fuse. Again, as soon as the key hit RUN, the fuse popped.

Another observation since this started: The engine always seems like it's running totally fine until the SES light itself comes on. When the fuse blows it doesn't seem like it's affecting anything. (Of course, I have stage 2 cams with a pretty small LSA, so it usually runs pretty rough, anyways.)

Thoughts?

 

[Tripoli]

Well, I decided to try cutting the suspect O2 sensor out again. I clipped the wires and taped them off so they wouldn't short. Last time, I gave it a few minutes to see if the fuse would blow and it never did. I did the same thing this time, and again the fuse did not blow. So, I went and drove it around for about 2 minutes and POP...it blew.

I can't seem to find any pattern. Sometime it blows before the starter even gets engaged, sometimes it takes 10 minutes of driving around.

 

[Tripoli]

Another update. I caved in and took the car to Ford this morning. They worked on it from 7:00 am until 3:00 pm and said they were 99% sure it was the passenger side upstream O2 sensor heater that was shorting, but said they couldn't test it until the car was cold, which after a long day of testing, it was not. With the car warm, they were unable to get the fuse to blow. (BTW, the tech has worked on Fords for 40 years.)

So they said to drive it home and see if the fuse would blow after the car had cooled down. On the way home, the fuse blew. So, hoping it was the passenger-side O2, I unplugged it, put in a new fuse and started driving her around. Turned the car off and on about three times, driving maybe half a mile inbetween, each time checking the fuse. Didn't blow. So I took her on the highway accelerating quickly. When I got off at the next exit, she was running rough. I pulled over and sure enough, the fuse was blown again. That 100% eliminates either upsteam O2 sensors now.

With the fuse blown, I proceeded to test the EVR for voltage. Nothing. Put in a new fuse, and sure enough there was power. I also tested the resistance of the EVR and it was fine. I left it unplugged and did my same driving routine as before. Just the same, after the fast acceleration onto the highway, the fuse was blown.

I don't know where the EVAP canister purge valve is to check it. Even though the dealership supposedly did check it and the canister itself, I feel as though I somehow am having better success blowing fuses, so I'd like to continue these tests one component at a time. Having eliminated both upstream O2s and the EVR, I could now use some more guidance.

 

[Mike97gt]

Another update. I caved in and took the car to Ford this morning. They worked on it from 7:00 am until 3:00 pm and said they were 99% sure it was the passenger side upstream O2 sensor heater that was shorting, but said they couldn't test it until the car was cold, which after a long day of testing, it was not. With the car warm, they were unable to get the fuse to blow. (BTW, the tech has worked on Fords for 40 years.)

So they said to drive it home and see if the fuse would blow after the car had cooled down. On the way home, the fuse blew. So, hoping it was the passenger-side O2, I unplugged it, put in a new fuse and started driving her around. Turned the car off and on about three times, driving maybe half a mile inbetween, each time checking the fuse. Didn't blow. So I took her on the highway accelerating quickly. When I got off at the next exit, she was running rough. I pulled over and sure enough, the fuse was blown again. That 100% eliminates either upsteam O2 sensors now.

With the fuse blown, I proceeded to test the EVR for voltage. Nothing. Put in a new fuse, and sure enough there was power. I also tested the resistance of the EVR and it was fine. I left it unplugged and did my same driving routine as before. Just the same, after the fast acceleration onto the highway, the fuse was blown.

I don't know where the EVAP canister purge valve is to check it. Even though the dealership supposedly did check it and the canister itself, I feel as though I somehow am having better success blowing fuses, so I'd like to continue these tests one component at a time. Having eliminated both upstream O2s and the EVR, I could now use some more guidance.

You eliminated the sensors themselfs but not the HARNESS or PCM.. I bet you have a damaged harness

 

[Tripoli]

Oh this just keeps getting better and better. I still have had no luck, but I found a very odd pattern to when this fuse is blowing.

I back out of my driveway, then turn left and go about 100 yards to a stop sign. I turn left and accelerate to 30 mph and cruise 7/10 of a mile in 4th or 5th gear, going over several fairly dramatic dips in the road along the way. I come to another stop sign. I turn left and accelerate to 30 or 35. About 100 yards after that turn, right about when I stop accelerating, the fuse blows. It's done this three times in a row in the EXACT same spot on that road.

These three tests were as follows:

1. Unplugged EVAP plug behind driver's side rear tire.
2. Plugged that back in and unplugged the upstream O2 sensor extensions that came with the L/T headers.
3. Left the O2s unplugged and also unplugged the EVAP and EGR Electronic Vacuum Regulator.

Before driving that route each time I tried starting and shutting off the motor a different number of times. For the first run, I started and let it idle a couple minutes, shut it down, started, shut down, checked fuse (OK), then drove. The second runI only shut down once and check the fuse (OK), then drove. The third time, I started and did not shut down before driving. Each time I reset the computer before these tests. Each time I saw the fuse blow at exactly the same point on the drive.

This is just weird.

 

[Pearl02]

Sorry your having so much trouble with it. I wish I had some answers for you. I have trouble finding problems like the ones you are having. It took me 2yrs to diagnois a drive train noise problem on my Mazda B-4000 pickup. I checked everything a bunch of times. Turns out the center carriar bearing was the problem. Just keep plugging away at it. Pearl02.

 

[Tripoli]

I've now tested the circuit with all 5 components unplugged at any given point, and the fuse still blows, and almost always at the same spot on my test drive, which is the only point on the drive that I get to about 35 MPH and over 2,500 RPM.

It's got to be a short somewhere in the wires that lead to or from these devices. I think my test driving might be providing a clue as to whice device is causing the problem. Does one of these devices only kick on after you exceed a certain speed or RPM?

Upstream O2 sensors & heaters.
Vapor Management Valve
ERG Electronic Vacuum REgulator
EVAP canister

Is it at all possible that my new Ford-rebuilt alternator could somehow be to blame for this? Is it okay to unplug the alternator and voltage regulator and drive around for a couple miles to test this?

 

[Tripoli]

A possible breakthrough?

A friend and I were trying to very thoroughly trace the wires tonight. We poked around a while and stripped away some of the plastic protecting the wires where they enter the engine compartment. We found the tell-take red/yellow wire that belongs to this circuit. We cut it and drove around to see if it still blew the fuse, and it did.

We didn't have much luck following the wire under the dash on the driver's side, but we were able to find it coming out from under the dash (apparently from the fuse box) on the passenger side right next to the PCM. From there it appeared to go directly up into the fender area and then out into the engine bay where we made the first cut. It did not appear to actually go into the PCM, to my surprise. So, we cut the wire again right there, guessing the short might be somewhere in the 2 feet between there and the first cut.

We drove the usual path again and parked to check the fuse. Still good. Interesting. So we took the car on about a 5-6 mile trip. Suspecting that the motion of the car, especially sudden decelaration, might cause the short, I rocked the car fairly violently in first gear, tried harsh breaking, etc. Fuse still good. Drove home after that. Still good.

I'm going to leave the wire cut for now and continue driving for a couple days to see if the fuse continues to stay good. Best I can figure, the wire we cut controls the upstream O2s, the EGR EVR, and the Vapor Management Valve, all of which have been tested.

God willing, we've found the problem. Will report back when I have more news.

 

[Pearl02]

That's great news. I hope you found the problem. I absolutely hate wire problems. They can be very hard to track down as you know. Pearl02.

 

[04_chucktown_V6]

Any more developments?

I am having the same issue you are having. I have not gotten into as much depth in testing the individual components but my #8 fuse keeps blowing as well. I replaced my O2 sensors so I dont think it is those. The connector on one of the previous O2 sensors was lieing on the header and melted as well, just like yours, so that is the reason why I replaced those.

I was just wondering if you have had your fuse blow anymore after making that last cut in that wire. Please post an update, thanks!

 

[Tripoli]

My fuse is still good after making that last cut. Since, I have spliced a new wire in its place; however, I seem to have bypassed the EVAP purge valve solenoid, located inside the right-front fender well. I'll be going in again to fix that. I'm concerned that that still won't fix the one code about the passive anti-theft system, so we'll see what happens after I fix the EVAP stuff.

 

[04_chucktown_V6]

So by cutting those wires are you disabling all of those components or only a certain one? I am asking because ever since my fuse blew, I have gotten horrible throttle response and overall performance when it comes to power. If I make the same cut that you made, will I just be disabling the O2 sensors and other components all together and just keeping the fuse from blowing? Or will I just be disabling the component that is making the fuse blow? I hope I am not confusing you in my question. Thanks for the update.

 

[Tripoli]

If you cut the wire, you'll be disabling all, or at least most, of the circuit, which includes the upstream O2s, the EVAP system, and the ERG system. The O2s are what causes the problems with the engine running properly. I found that unplugging the upstream O2s from the circuit helped with idle quality significantly, though you still don't want to run the engine up too high, because you won't be running the optimal air/fuel mixture.

In my case, we tested all the components and none of them were causing the short, though it is possible that one of them could be your problem. Unplugging them one at a time and driving around for a while is the only way to test this, and it can be quite a pain, unfortunately.

 

[Tripoli]

Been a while since I've worked on this, but I'm doing a head swap in a week or two and I want my engine codes gone by then.

I've continued playing around with the wires in the fender area near the PCM and under the hood. I'm down to these codes:

P0155 - Upstream Heated Oxygen Sensor Heater circuit fault - Bank No. 2.
P1151 - Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 2.
P1451 - EVAP Control System Canister Vent Solenoid Circuit Malfunction

Let's start with P0155 and P1151. How can these two codes coexist? Will solving P0155 likely solve P1151 by simply making the circuit active again?

P0155 and P1451 are obviously both symptoms of my original problem, which is a short to ground somewhere on the circuit. I have still not been able to locate the short. I attempted bypassing a small portion of the circuit between the PCM and the engine bay with some success. This apparently bypassed part of the EVAP system located inside the passenger-side fender. I fixed this by running a new power wire from my bypass wire directly to the device, and I haven't seen that code since. I'm pretty sure I know what's causing P0155 to kick on, which is one of the wires I cut in attempting to get rid of the short (I think/hope). My first task in the morning will be to splice those wires back together like they were to begin with. Hopefully that will narrow me down to just....

P1451. Can someone confirm that the wires for this circuit are the ones that run to the EVAP canister itself, located above the driver-side tailpipe? I have traced the power wire for that device forward along the driver-side door sill under the edge of the carpet, but I loose it once it gets to the kick panel next to the dead pedal. Can anyone tell me where this specific red/yellow wire disappears to? I would assume that it heads for either the fuse box or across to the PCM, but I just can't spot it.

 

[Tripoli]

Well, I seem to have solved almost everything, expect I'm still getting one code: P1151 - Bank 2 lean. Any ideas?