Hello everyone,

I have a 96 Blazer with the 4L60E automatic transmission. The truck has 265,000 miles and this is the 2nd transmission, replaced 15 years ago at about 150k. I always change the trans fluid / filter every 30,000 miles and the trans has about 27,000 miles since last change. I recently had a code p1870 and the transmission stopped going into 4th gear, very noticeable at ~60 mph. I checked the transmission fluid and it was about a half quart too low so I added to hot fill line. I cleared the code with my code reader and test drove the vehicle. Despite the fluid now being at correct level, it still would not go into 4th gear. In addition, after 2 more short trips to test drive the Service Engine Soon Light fired again with same P1870 code.

Here is the question -- Before I take it to the transmission shop, should I try to change filter / fluid and see if that resolves? Or would that just be a waste of time? If the low fluid was the root cause then what needs to be done to reset?

Thanks everyone,
Mike