I had my 2001 Ram 2500 out today. Coming home from work I noticed the check engine light was one. All my gauges read where they should so I kept driving. When I got home, I flipped the key to get the code. P1821. I went into the garage and got my scan tool. It got the same code and said the engine had been too cold too long. The temp. gauge was in the normal range all the way home. I'm pretty sure I've got two temperature sending units. Anybody know which is which on the 5.9 gas engine? I'm sure one is for the gauge and the other for the computer. At $20 a pop I don't want to replace both of them. This is a tight time of year for me. A couple of months down the road I'll be flush but winter is slow in the roofing business. Thanks.