Check Engine Light - Code Diagnosis Help Please

My check engine light has been coming on after cruising between 55mph and 60mph for about 10 minutes. This had actually been going on for the last 50,000 miles. But, once I turn the van off and back on the CEL stays off. I finally pulled the codes today and I get a #51.

Things to note right now.
- AC belt is not on.
- Reverse lights don't work due to a bad neutral start switch.

Based on the above notes code 51 makes sense right?

But this doesn't help diagnose the CEL after 55mph to 60mph cruising. Thoughts?

The van runs perfect so I'm not worried. It's just bugging me.

My understanding is that the CEL going off doesn't mean much of anything at all, which was hard for me to wrap my head around at first. Just because the CEL goes on and off at either random or seemingly predictable intervals does not mean that there is a relation and the CEL turning off does not mean that the problem is intermittent or has somehow resolved itself.

As far as your 51 code, all indicators point to your TPS. Earlier this year, I had 3 stored codes, one of them was a code 51. A new TPS sensor took care of that code, and the van runs great. I'll throw in a quote from Tim for good measure.

Quote:

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Originally Posted by timsrv

Clear codes, drive it some more & recheck codes. If #51 comes back you most likely have a bad TPS. These are a common failed part on the van. If it's got more than 150k miles on it or if you don't know how old it is, then I'd just replace. Testing these per the manual is a somewhat involved process. I'm not saying he didn't do it right, but it's hard to imagine your average mechanic going to this much effort (it would be hard to do with the throttle body installed). Even if he did do everything right, when these get old they become intermittent. Bottom line? For a $35 part it's not worth messing with. I replace these like some people replace spark plugs. If I'm doing a tune-up and I see code 51, I won't even mess around with trying to clean or whatever. Just replace it and be done with it . Tim

PS: If it's newer and you know it's got less than 100k miles on it, then perhaps it's worth a little more consideration. But for me, my time is more valuable than messing with a questionable TPS. Tim

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EDIT: Your other symptoms may also be contributing to the code 51, but if you don't know mileage or age of TPS then I would replace. If nothing else it's cheap "preventative maintenance."

Cool, thanks. I ordered a TPS. Will let everyone know if this resolves the issue.

I had similar symptoms with a new TPS (installed by PO's mech). I removed the TB and reset the TPS. 51 still there. At the same time I suspected a vacuum leak in the area of the TPS. The big sucking sound got worse and worse, and worse. Finally I found it - bad EGR gasket. I fixed it and the code went away (van also runs MUCH better). I'm not sure if that jives with what we would expect, but my check engine light used to come on at highway speeds and it doesn't any more. I replaced the gasket and no longer have a code 51. FWIW, I also have my A/C belt removed. I'll also mention that the PO did not put in a Toyota TPS. Personally, I would have installed a Toyota TPS. I almost replaced it in an attempt to get rid of the 51, but all seems fine now. Here are a few shots of my bad gasket.

I'm not sure if there is a connection or not, but after repairing the EGR gasket I immediately got code 21 (O2). Replaced that (definitely expired) and 21 went away.

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