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Discussion Starter #1 (Edited)
Sorry in advance for the long post. I’ve seen so many people post minimal information with their issue and it usually just generates responses asking for more information. So here is everything I can think of to help explain what’s going on…

I have a 2003 Taurus SSE (6cyl-FFV OHV) with about 130K miles. It was owned by my wife’s grandmother until she passed away about 4 years ago, and then the car was given to my son. It was in immaculate condition at the time and had been maintained very well. Other than a few maintenance issues, it looked and ran like new. My son was 23 at the time. He’s a singer/songwriter and spends a lot of time on the road. He’s driven all kinds of cars without so much as a ticket, but within a month of getting this Taurus he had his first accident on the way to a gig. Mostly it was just body damage, but it took him 6-months to save for all the repairs. A few weeks after getting it back from the shop, he was playing a pretty big gig out of town. Normally he would ride with the band but he just got the car back from the shop and wanted to ride in comfort this trip. When leaving that city to head back the next morning he had another accident, although not his fault this time. Pretty much the exact same body damage occurred. Nothing mechanical was affected according to the shop.

Soon after getting it back from the shop following the second accident, problems began popping up like spring flowers. However, because of this forum, I’ve been able to identify and repair most everything we encountered thanks to others who had posted similar issues in the past… at least until now that is.

A few weeks ago, my son was driving to yet another big gig a few hours from home and another member of his band was riding with him. About halfway there he called to tell me the CEL came on and was flashing. I had just driven the car a week earlier and knew it was running smooth as silk, so I was surprised to hear this. He said it still seemed to be running just fine, but after the CEL came on he noticed the shifting felt a little off, like when the camshaft synchronizer and an assortment of other things went bad 18 months ago.

He was way out in the country but close to a small city, so I told him to find a local auto parts store and have them read the codes. He called back and said they found 3 codes. They didn’t give him the code numbers, only what the codes were related to. They also cleared the codes off without asking him first.

The codes were associated with:
1. Catalytic converter
2. Gas Cap
3. Cylinder 6 misfire

Since this night was a big event for him, I told him he could probably continue on as long as the car felt and sounded ok, but just to pay close attention to the gauges and to stop if the CEL came back on. About 15 minutes later, he called and said the transmission light had now come on and was also flashing. No new symptoms, just the warning light. The guy with him quickly found some information online about it suggesting they pull over immediately and that the transmission may be overheating. They were only a few miles past a safe place to stop, so they turned around and went back there. After letting things cool down for a bit, he started the car and the transmission light was off now. He let it idle for 30 minutes and the light remained off, but when they started driving the light came back on within a few miles and the low gears were taking too long to shift and shifting hard when they did. By now they were back to the town with the auto parts store and they pulled into a Walmart parking lot. It was more than an hour away from home but two more hours to reach his gig. At this point they had little choice but to cancel the gig and just focus on getting back home. A mechanic who recognized them stopped to help. He couldn’t do much there but suggested putting some TranX in the transmission fluid to help them limp back home. So they got a bottle in Walmart and put some in.

No idea if the TranX really helped or not, but none of the warning lights came on the entire ride home, at least not while they were still on the highway. However, within 2 minutes of exiting the highway, the transmission light began flashing again while driving down a side road close to home. The gear shifting still felt hard, but other than that they didn’t notice anything different. The only similarity between each of the three times the transmission light came on was the speed they were driving at the time it came on. Slower speeds and a hot transmission seemed to trigger the light. Idling and cruising speeds seemed to be ok.

I wasn’t able to look at the car until a few days later, but when I started the engine it just purred like a kitten. It all felt and sounded completely normal, so I took it for a very short drive. When driving in first gear it felt like the low gear didn’t know when to shift and would kick once it did. When driving in a parking lot, going back and forth between 1st and 2nd gear felt like I was riding on a mechanical bull. I never did see any warning lights, but I may not have driven it long enough for it to heat up much. So, I returned home to begin digging. When I got out of the car I smelled something unusual – partly like a hot engine and partly like new brakes smell after friction begins wearing the pads. I checked under the hood but couldn’t pinpoint the source. The transmission fluid was the normal red/pink color and didn’t smell burned at all. Nothing else I checked smelled burned either.

Trying to identify issues related to the individual codes or answers to the transmission light coming on hasn’t been very successful. My experience with these codes is that they are often downline symptoms of a separate issue or failure. The very idea that the transmission is the underlying problem is hard for me to believe, especially since there were no symptoms whatsoever until after these CEL codes were recorded. I checked for vacuum leaks and made sure none of the wires or sensors had come loose but found nothing.

Something I had read made me think there could be a blockage in the catalytic converter, or possibly a carbon buildup somewhere in-between. I talked to a few mechanics I use for bigger jobs and they both said it’s likely the transmission. Perhaps it is, but I would need more convincing before I can believe that. So, I had my son get under the car and tap on the catalytic converter to see if he could hear anything rattling, but it sounded pretty solid. Then I decided to change the EGR valve and see if it had any impact to anything. I also put clamps on a few vacuum lines and hoses that were loose, cleaned the throttle body, and reset the computer by completing the positive and negative circuit and leaving it overnight (with the terminals off the battery).

The result was that when I tried starting the car it was barely able to stay running. It was bogging severely before it finally stalled after a minute, much like you’d expect with a banana in the tailpipe or only having 1 of 6 cylinders connected. I restarted it and tried pressing the gas. I couldn’t keep it running long enough to look at what I was hearing but it sounded like a popping/crackling that slowly began after a few seconds and gradually increased in intensity over the next 10-15 seconds, kind of like cooking popcorn. So I turned the ignition off. In the engine I saw small puffs of smoke coming off the back of the engine block around the O2 sensor. I wondered if maybe I jarred some carbon buildup or something loose when changing the EGR valve and it caused a clog somewhere. I double-checked to make sure I’d reconnected all the vacuum lines and sensors but didn’t find anything out of place.

I couldn’t be certain this wasn’t the result of installing a bad EGR valve or inadvertently blocking a vacuum line with the clamps I installed, so I took all the new clamps off and reinstalled the old EGR valve.

There was no change after putting everything back the way it was when it purred like a kitten. It was still bogging and popping like I described above when installing the new EGR valve. I wasn’t able to keep it running long enough to generate a CEL or any codes.

So that’s where I’m at. I still suspect a blockage somewhere or possibly a bad O2 sensor or catalytic converter. The nut on the pipe that connects to the bottom of the EGR valve took a lot of force to break and may have caused something to jar loose inside. It could also be another sensor or part but I don’t have any convincing evidence to say which one. There is a part/sensor on top of the throttle body that I removed and carefully wiped off but the part name is escaping me at the moment. It has two holes that line up on the throttle body and connects to a wire harness. There’s also a label on it that says not to try and clean the part (and I didn’t).

Sorry for the length. I didn’t want to leave anything off that might help some fellow troubleshooters out there. Any suggestions, ideas, or additional questions are appreciated (other than my son using a different car for his gigs).

I need as much help as I can get at this point. Thanks!

Super Moderator
8,066 Posts
We need to know the exact codes to help you. There is no such thing as a "gas cap" code.

If the cat codes were P0420 and/or P0430, the cats are shot (420 = rear bank cat shot, 430 = front bank cat shot). Failing post cat O2 sensors will not set 420/430 codes.

Driving more than a few minutes with a flashing CEL (flashing CEL = BAD missfire) will kill a cat.

Missfire codes on Vulcans are almost always due to cracks in the coil pack, but could be bad plug wires or bad plugs. First step is to pull the coil pack and look for any cracks, especially on the bottom. If ANY cracks are found anywhere, replace the coil pack with ONLY the Motorcraft or BWD (Borg Warner) part.

Ford EGR valves VERY rarely fail, and a failing / failed DPFE will set a 400 series code (P0401, P0402, P1400, etc)

3 Posts
Discussion Starter #3
Thanks Jeff.

Unfortunately, I have no way to get the codes since they were cleared and have not reoccurred again.

I've gotten the gas cap description for certain codes on this car in the past. It's not a designated code, but a group of codes that can be triggered by a gas cap issue, among other things (P0440-P0443, P0446, P0453, P0455, P0456). When my scanner reads one of those codes it lists the gas cap first as a possible cause and then a few other possibilities.

I'm not all that familiar with the exhaust system and catalytic converter components. I've done most all the work on my cars over the last 35 years but have never encountered an issue in these areas. I no formal training. I just like troubleshooting issues that come up and enjoy finding and fixing problems... mostly because I'm a major cheapskate. I'm not afraid to dig in and learn as I go, and after all this time I'm still amazed at how often I'm dealing with issues I've never had or learned anything about. So this would be my first experience with catalytic converter issues, terminology, codes, and a lot of the function in and around it. I've just never had to deal with it before.

I'm not clear on what the front and rear cat banks are. Any idea where I can quickly learn more about this and the related systems?
"Failing post cat 02 sensors will not set 420/430 codes". So, if either of these codes was triggered then the problem wouldn't be the O2 sensor. Is that what you were saying?

The coil pack was replaced a few years ago but I will double check it for any cracks. I also need to check the wires, plugs, and injectors. idle RPM's were normal and the engine was running smooth up until I pulled the EGR valve off.

Do you know how common it is for the Idle Air Control Valve/Motor to fail? Or the EGR Valve Pressure Sensor? I'm a little concerned that I may have done something to the Idle Air Control Valve/Motor when I pulled it off the throttle body. I don't know how sensitive these are but I held it upside down and tried to wipe the carbon from inside the two ports, and now it won't idle. It may be unrelated but I do have to consider that I might have created the problem when installing the new EGR valve (which I ended up taking out and reinstalled the old one).

I've gotten a few misfire codes in the past but didn't find any issues, and they were ultimately cleared up after correcting a sensor failure and resetting the computer. Since the engine was running perfectly fine when the CEL came on, it may be the case here where the misfire was a momentary issue or downline symptom caused by something else. Whatever it was it didn't stay a problem for long and hasn't reoccurred since. I don't know what other secondary codes or downline symptoms are possible with the P0420/P0430 codes, but I will look into that and see if I can draw any connections.

If I did get one of these cat failure codes 420/430, does this mean I would need a new cat? Since the codes were erased before I was able to see them I really don't know if either of these codes were triggered. Wouldn't they continue to come back and turn the CEL back on after being erased? I guess that's what has me so confused by everything, because none of these error codes ever came back after being erased and nothing was out out of the ordinary until the transmission light came on. There wasn't any progression of problems until I messed with the EGR valve, and now I can't keep it running long enough for any warning lights to even come on. Obviously the EGR valve wasn't the problem, but is there anything you can think of that might have triggered this inability to idle simply by changing the EGR valve and lightly tapping on the cat? Is there any way to clean out the pipe that connects from the bottom of the EGR valve to the manifold by the O2 sensor? The bogging began the instant I started the car and the popcorn popping sound right after that, so I can't help wondering if the force from breaking that EGR nut didn't jar some carbon loose in that pipe to the EGR valve and either compound the cat code issue or clog up the manifold. But I'm just spitballing. Any other thoughts on where to go with this?

Sorry to write so much. I was just hoping that more information might cause someone to recall something they've seen or experienced before or have an idea about something to check. These codes are usually just a place to begin, and in this case there is clearly a greater problem going on that created these other symptoms. It's harder without the actual code numbers, but that's why I'm giving as much detail as possible.

Thanks again!
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