1998 Saturn SC1 Doesn't shift after engine gets hot

1998 SATURN SC1
10,200 MILES • 4 CYL • 2WD • AUTOMATIC
Avatar
STEVENEWBY
  • MEMBER
  • 2 POSTS
My daughter's car wants to remain in low gear (yes, it's an automatic transmission) when she gets caught in rush hour traffic and engine heats up. She claims the RPM's are about 5,000 to go 30 mph. Is this the transmission control unit acting up intermittently? On her typical drive to work or class she has no issues. She took it to the Saturn dealer and they took her $40 for computer diagnostics, but then said they'd need more money to determine the actual cause of the computer transmission fault code. It's an old car and we don't want to spend a lot to repair it. How much is a new TCU? Is it something I can replace for her?
Her Dad
Oct 24, 2008 at 5:58 PM
Advertisement
Avatar
MASTERTECHTIM
  • CAR REPAIR CONTRIBUTOR
  • 4,750 POSTS
go to autozone and have them scan the computer for codes. they do it for free then get back to us with the codes and we can go from there.
Oct 24, 2008 at 6:46 PM
Avatar
STEVENEWBY
  • MEMBER
  • 2 POSTS
Per AutoZone:
P0732 gear 2 ratio incorrect
P0733 gear 3 ratio incorrect
P0734 gear 4 ratio incorrect

Could the transmission be slipping? Only when it gets hot? Based on the RPM's per my daughter's observations, she wouldn't get close to 5000 RPM's at 30 mph even in low gear if it wasn't.

Transmission fluid level appears normal and car regularly has oil changed and fluids topped off at Saturn dealership.
Oct 28, 2008 at 6:41 PM
Avatar
MASTERTECHTIM
  • CAR REPAIR CONTRIBUTOR
  • 4,750 POSTS
its definitely possible for a slipping transmission to be causing your problems but its also possible a bad shift solenoid or input sensor or a broken power wire going to transmission. definitely stop driving and my suggestion is to take it to a trans shop for diagnosis. this is tricky for a tech to properly diagnose so i wouldnt wanyt you to go down a wrong path, the diagnosis usually wont take longer than a hour.
Oct 28, 2008 at 6:53 PM
Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.