codes p0302, 133, 174, 171

My sister has a 98 windstar 3.8 (140k) and has a blinking CEL. She took it to autozone and got codes 302, 133, 174, 171. I know that 302 is a #2 cyl misfire, and that 174 and 171 are o2 sensors for #'s 1 and 2 banks. I don't know what 133 is. I've been reading as many threads as I can to see how the codes are related and what the easiest/cheapest fix might be. Any help would be greatly appreciated. She also has the infamous passenger side power window inop and the perma-illuminated dome light, but I found how to remedy those.

171 and 174 indicate that the o2 sensors are detecting a lean condition. It does not necessarily mean there is anything wrong with the O2 sensors.

However code 133 - O2 sensor circuit slow response (Bank 1 sensor 1) which may or may not be a little more specific to the O2 sensor.

Normally a lean condition is caused by an intake leak and the fact that you have it in both banks tends to indicate a common failure mode for both banks. The misfire can often be caused by clogged or partially clogged EGR ports.

The misfire is what is causing your flashing light (indicating immediate action required). I would suggest tackling this one first and as I said more than likely clogged EGR ports. (The unclogging procedure is outlined in the forum somewhere)

There are TSBs for intake leaks on 99s and up but there may be one for your sister's years two. (again search for something like "98 intake leaks" or similar.

After this I would see if the O2 code goes away. If not then it may be time to really look into that particular sensor. Perhaps swaping banks to see if the failure follows the sensor or not right up to possibly replacing it if need be.


Good luck. Post back often and the good folks here will help every step of the way.

Would an intake leak be an intake manifold gasket? I read on a couple threads that if you experience abnormal coolant loss that that could be a culprit, and she has had empty coolant reservoirs on more than one occasion.

An intake manifold leak could certainly cause a lean condition. A leaking intake could also cause a misfire especially if coolant is getting into a cylinder.

Coolant is also not good for O2 sensors so if you suspect an intake leak I would look into that right away

Thanks DRW. Hopefully she can get this thing fixed. I've seen you all over this forum and you seem to know what your talking about, so I appreciate your help.

I had the P302 & 174, replaced plug wires and haven't seen CEL since then. Spraying WD-40 around the intake gaskets will expose a leak as a rev in the engine, has to be running of course.

these codes are notorious on windstars. at our shop we replace the lower intake manifold gaskets, the plenum gasket with the new rubber insulators and bolts, and also there is an updated front valve cover that reduces the crankcase pressure.

it's an expensive job to do and I've done 10 or 12 in the last year. big problem with the windstars. otherwise they are pretty good cars though. good luck.

oh yeah, ps. those codes are hard to diagnose without a scantool, but it's so common it's pathetic. Symptoms are worse in the a.m. when it's cold. The intake gaskets leak more and cause a worse running problem. hope this helps!