Son has a 2001 s-10.It has the 4cyl engine with automatic tranny.On the road it will run great then suddenly drop
out of overdrive and downshift.The only way to get this back in overdrive is to stop, and start all over again from the
start.The fluid is full and clean.Any suggestions?
Put a code reader on it. It might be the speed sensor but it would be worth your money to know before buying one and that not being the problem. The sensors range from $20 to $85.
Determine if the vehicle is equipped with a MAF sensor. If the MAF sensor elements are coated with contaminents, such as oil and/or dirt, then the Powertrain Control Module (PCM) will not receive correct airflow/load input from the MAF sensor. This usually causes a lean air/fuel condition but also is known to cause lower than expected transmission line pressure. Most of the time, cleaning the sensor elements with a cotton swab and electrical contact or MAF cleaner will fix the incorrect MAF signal and allow transmission line pressure to return to normal. GM has a bulletin, #04-07-30-013B, related to this condition, but refers only to aftermarket air filters as the cause. Have confirmed many vehicles with an OEM air filter that have this condition.
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