Engine torque signal circuit & P1781 code

[Bob J]

Hi guys, I have looked through the posts here about Engine torque signal circuit & P1781 codes and was hoping there is some newer wisdom than 2012.

My code reader shows these two items, and the car seems to follow some of the symptoms described in earlier posts.
Very rough idling on startup, sometimes blinking check engine light, sometimes no 4th gear, when there is no 4th, I just pull over and shut her down for a minute, then she's fine for the rest of the day. I also just had the tranny fluid flushed & filter changed.

I have replaced the plugs and they looked great, did the wires too. How often does a coil pack go bad? or if it is the coil pack why is the car running like a champ most of the time, I'd hate to have to take it to the Chevy dealer and have the heads redone and not fix the problem.

I have 114K miles on my 2004 hatchback, and just love the car. The belt was changed before 60K and I suppose I need to change it again, is that right?

Thanks,
Bob J in Wisconsin

[avguy]

... I'd hate to have to take it to the Chevy dealer and have the heads redone ....

Can't imagine ever doing that for no reason (i.e. if compression is fine). And my choice wouldn't be to do any other part-hanging either.

The best approach (by far) for diagnosing anything like this is to monitor with a real-time OBD data stream reader. You can do this inexpensively with the Android Torque app, or buy a commercial reader off the shelf. The real-time data stream will provide important information, such as fuel trim, Map, etc. At the point when the vehicle begins to run poorly, one or more OBD values will change, and it's likely to provide important clues to what's going on. It might take more than one try, but it sounds like that won't be a problem in your case.

Another thing you can try is electrical diagnostic testing with a multi-meter when it's running poorly. Check the battery running voltage, including a short load test. And also check the voltage drop on the big wires, and gently move wire bundles around with your hands as well. All very easy things to do.

A systematic diagnostic approach is what I'd recommend, but lots of people aren't willing to get into that. Your vehicle, your choice.

If the 3 other parts in the timing belt loop were not changed along with the belt at 60K, then definitely replace all 4 of them asap.

[Bob J]

Thanks for the reply Avguy, I don't think the other stuff was changed @ 60K. I'm now moving up from the nickle & dime stuff into the quarters.